Chiton
Encyclopedia
Chitons are small to large, primitive marine
molluscs in the class
Polyplacophora.
There are 900 to 1,000 extant species
of chitons in the class, which was formerly known as Amphineura.
These molluscs are also sometimes commonly known as sea cradles or "coat-of-mail shells". They are also sometimes referred to more formally as loricates, polyplacophorans, and rarely as polyplacophores.
Chitons have a dorsal shell which is composed of eight separate shell plates or valves. These plates overlap somewhat at the front and back edges, and yet the plates articulate well with one another. Because of this, although the plates provide good protection for impacts from above, they nonetheless permit the chiton to flex upward when needed for locomotion over uneven surfaces, and also the animal can slowly curl up into a ball when it is dislodged from the underlying surface. The shell plates are surrounded by a structure known as a girdle.
Chitons live worldwide, in cold water and in the tropics. Most of them inhabit intertidal or subtidal zones and do not extend beyond the photic zone
.
They live on hard surfaces, such as on or under rocks, or in rock crevices. Some species live quite high in the intertidal zone
and are exposed to the air and light for long periods. Others live subtidally. A few species live in deep water, as deep as 6000 metres (19,685 ft).
Chitons are exclusively and fully marine. This is in contrast to the bivalves
which were able to adapt to brackish water
and freshwater, and the gastropods
which were able to make successful transitions to freshwater and terrestrial environments.
The calcareous valve
s that chitons carry dorsally
are protective, made wholly of aragonite
, and variously colored, patterned, smooth or sculptured. The shell is divided into eight articulating calcareous
(aragonite) valve
s embedded in the tough muscular girdle that surrounds the chiton's body. This arrangement allows chitons to roll into a protective ball when dislodged and to cling tightly to irregular surfaces.
The most anterior plate is crescent shaped, and is known as the cephalic plate (sometimes called a "head plate", despite the absence of a complete head). The most posterior plate is known as the anal plate (sometimes called the "tail plate", although chitons do not have a tail.)
The front seven plates develop simultaneously, with the rear plate being added later in the developmental process. Growth lines are formed each winter. The inner layer of each of the six intermediate plates is produced anteriorly as an articulating flange. This is called the articulamentum. This inner layer may also be produced laterally in the form of notched insertion plates. These function as an attachment of the valve plates to the soft body. A similar series of insertion plates may be attached to the convex anterior border of the cephalic plate or the convex posterior border of the anal plate.
The sculpture of the valves is one of the taxonomic characteristics, along with the granulation or spinulation of the girdle
After a chiton dies, the individual valves which make up the 8-part shell come apart because the girdle is no longer holding them together, and then the plates sometimes wash up in beach drift. The individual shell plates from a chiton are sometimes known as "butterfly shells" because of their shape.
The protein component of the scales and sclerites is minuscule in comparison with other biomineralized structures, whereas the total proportion of matrix is higher than in mollusc shells. This implies that polysaccharides make up the bulk of the matrix. The girdle spines often bear length-parallel striations.
The wide form of girdle ornament suggests that it serves a secondary role; chitons can survive perfectly well without them. Camouflage or defence are two likely functions.
-like foot, but no head or other soft-parts beyond the girdle are visible from the dorsal side.
The mantle cavity
consists of a narrow channel on each side, lying between the body and the girdle. Water enters the cavity through openings either side of the mouth, then flows along the channel to a second, exhalant, opening close to the anus
. Multiple gill
s hang down into the mantle cavity along part or all of the lateral pallial groove, each consisting of a central axis with a number of flattened filaments through which oxygen can be absorbed.
The heart has three chambers and is located towards the animal's hind end. Each of the two auricles collects blood from the gills on one side, while the muscular ventricle
pumps blood through the aorta
and round the body.
The excretory system consists of two nephridia
, which connect to the pericardial cavity
around the heart, and remove excreta through a pore that opens near the rear of the mantle cavity. The single gonad
is located in front of the heart, and releases gametes through a pair of pores just in front of those used for excretion.
The mouth
is located on the underside of the animal, and contains a tongue-like structure called a radula
, which has numerous rows of 17 teeth each. The teeth are coated with magnetite
, a hard ferric/ferrous oxide mineral. The radula is used to scrape microscopic algae off the substratum. The mouth cavity itself is lined with chitin
and is associated with a pair of salivary gland
s. Two sacs open from the back of the mouth, one containing the radula, and the other containing a protrusible sensory subradula organ that is pressed against the substratum to taste for food.
Cilia pull the food through the mouth in a stream of mucus
and through the oesophagus, where it is partially digested by enzymes from a pair of large pharyngeal
glands. The oesophagus in turn opens into a stomach
with where enzymes from a digestive gland complete the breakdown of the food. Nutrients are absorbed through the linings of the stomach and the first part of the intestine
. The intestine is divided in two by a sphincter
, with the latter part being highly coiled and functioning to compact the waste matter into faecal pellets. The anus
opens just behind the foot.
Chitons lack a clearly demarcated head; their nervous system resembles a dispersed ladder. There are no true ganglia
as there are in other molluscs, although there is a ring of dense neural tissue around the oesophagus. From this ring, nerves branch forwards to innervate the mouth and subradula, while two pairs of main nerve cords run back through the body. One pair, the pedal cords, innervate the foot, while the pallio-visceral cords innervate the mantle and remaining internal organs.
Some species bear an array of tentacles in front of the head.
s. The aesthetes consist of light sensitive cells just below the surface of the shell, although they are not capable of true vision. In some cases, however, they are modified to form ocelli, with a cluster of individual photoreceptor cells lying beneath a small lens. An individual chiton may have thousands of such ocelli
There is a relatively good fossil record of chiton shells, but ocelli are only present in those dating to or younger; this would make the ocelli, whose precise function is unclear, the most recent eyes to evolve.
Although chitons lack osphradia
, statocyst
s, and other sensory organs common to other molluscs, they do have numerous tactile nerve endings, especially on the girdle and within the mantle cavity.
However, chitons lack a cerebral ganglion.
of Chiton are known to exhibit homing behaviours, journeying to feed and then returning to the exact unique spot they previously inhabited. The specific method of how chitons can perform such behaviors has been investigated to some extent, however the reason remains unknown. Suggestions include the chitons remembering the topographic profile of the region, thus being able to guide themselves back to their home scar via a physical knowledge of the rocks and a visual input by their primitive eyes,
The gastropod Nerita textilis is known to deposit mucus as it moves, which a chemoreceptive organ is able to detect and guide the snail
back to its home site, It is unclear if chitons function in this manner. However, it is theorized that they may leave chemical cues along the rock surface and at the home scar which olfactory senses can detect and home in on. Furthermore, old trails may be detected, providing further stimulus for the Chiton to find its home,
Also, chitons have teeth made of magnetite on their radula making them unique among animals. This means they have an exceptionally abrasive tongue with which to scrape food from rocks. These crystals are thought to be involved in magnetoreception, the ability to sense the polarity or the inclination of the Earth's magnetic field, and to be involved in navigation.
, Tobago
and Barbados
. They were also eaten by native Americans of the Pacific coasts of both North and South America. The foot of the chiton is prepared in a manner similar to abalone
.
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A chiton creeps along slowly on a muscular foot. They have considerable power of adhesion
and can cling to rocks very powerfully, like a limpet
.
Chitons are herbivorous grazers. They eat algae, bryozoans, diatom
s and sometimes bacteria
by scraping the rocky substrate with their well-developed radula
.
A few species of chitons are predatory, such as the small western Pacific species Placiphorella velata. These predatory chitons have an enlarged anterior girdle. They catch other small invertebrate
s, such as shrimp
and possibly even small fish, by holding the enlarged, hood-like front end of the girdle up off the surface, and then clamping down on unsuspecting, shelter-seeking prey.
Some chitons exhibit homing behavior, returning to the same spot for the daylight hours and roaming around at night to feed.
Chitons have separate sexes, and fertilisation is external. The male releases sperm
into the water, while the female releases eggs either individually, or in a long string. In most cases, fertilisation takes place either in the surrounding water, or in the mantle cavity of the female. Some species brood the eggs within the mantle cavity, and the species Callistochiton viviparus even retains them within the ovary and gives birth to live young, an example of ovoviviparity
.
The eggs have a tough spiny coat, and usually hatch to release a free-swimming trochophore
larva, typical of many other mollusc groups. In a few cases, the trochophore remains within the egg (and is then called lecithotrophic – deriving nutrition from yolk), which hatches to produce a miniature adult. Unlike most other molluscs, there is no intermediate stage, or veliger
, between the trochophore and the adult. Instead, a segmented shell gland forms on one side of the larva, and a foot forms on the opposite side. When the larva is ready to become an adult, the body elongates, and the shell gland secretes the plates of the shell. Unlike the fully grown adult, the larva has a pair of simple eyes, although these may remain for some time in the immature adult.
, seastars, crab
s, lobster
and fish
.
of the Pacific Northwest
. In this species the valves are completely internal.
.
Kimberella
and Wiwaxia
of the Precambrian and Cambrian may be related to ancestral polyplacophora. Matthevia
is a Late Cambrian polyplacophoran preserved as individual pointed valves, and sometimes considered to be a chiton, although it can at best be a stem-group member of the group. Based on this and co-occurring fossils, one plausible hypothesis for the origin of polyplacophora has that they formed when an aberrant monoplacophoran was born with multiple centres of calcification, rather than the usual one. Selection quickly acted on the resultant conical shells to form them to overlap into protective armour; their original cones are homologous to the tips of the plates of modern chitons.
The chitons evolved from multiplacophora
during the palaeozoic, with their relatively conserved modern-day body plan being fixed by the mesozoic.
in 1758. Since his description of the first four species, chitons have been variously classified. They were called Cyclobranchians ("round arm") in the early 19th century, and then grouped with the aplacophorans in the subphylum
Amphineura in 1876. The class
Polyplacophora was named by J. E. Gray in 1821.
word chitōn, which means "mollusc", and in turn is derived from the Greek word "khitōn", meaning tunic
(which also is the source of the word chitin
). The Greek word "khitōn" can be traced to the Central Semitic word "*kittan", which is from the Akkadian
words "kitû" or "kita’um", meaning flax or linen, and originally the Sumerian
word "gada" or "gida".
The Greek-derived name Polyplacophora comes from the words poly- (many), plako- (tablet), and -phoros (bearing), a reference to the chiton's eight shell plates.
Since chitons were first described by Linnaeus (1758) there have been extensive taxonomic studies at the species level. However, the taxonomic classification at higher levels in the group has remained somewhat unsettled.
The most recent classification (Sirenko 2006) is based not only on shell morphology, as usual, but also other important features including aesthete
s, girdle, radula, gills, glands, egg hull projections and spermatozoids. It includes all the living and extinct genera of chitons.
This system is now generally accepted.
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
molluscs in the class
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
Polyplacophora.
There are 900 to 1,000 extant species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of chitons in the class, which was formerly known as Amphineura.
These molluscs are also sometimes commonly known as sea cradles or "coat-of-mail shells". They are also sometimes referred to more formally as loricates, polyplacophorans, and rarely as polyplacophores.
Chitons have a dorsal shell which is composed of eight separate shell plates or valves. These plates overlap somewhat at the front and back edges, and yet the plates articulate well with one another. Because of this, although the plates provide good protection for impacts from above, they nonetheless permit the chiton to flex upward when needed for locomotion over uneven surfaces, and also the animal can slowly curl up into a ball when it is dislodged from the underlying surface. The shell plates are surrounded by a structure known as a girdle.
Habitat
Photic zone
The photic zone or euphotic zone is the depth of the water in a lake or ocean that is exposed to sufficient sunlight for photosynthesis to occur...
.
They live on hard surfaces, such as on or under rocks, or in rock crevices. Some species live quite high in the intertidal zone
Intertidal zone
The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...
and are exposed to the air and light for long periods. Others live subtidally. A few species live in deep water, as deep as 6000 metres (19,685 ft).
Chitons are exclusively and fully marine. This is in contrast to the bivalves
Bivalvia
Bivalvia is a taxonomic class of marine and freshwater molluscs. This class includes clams, oysters, mussels, scallops, and many other families of molluscs that have two hinged shells...
which were able to adapt to brackish water
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...
and freshwater, and the gastropods
Gastropoda
The Gastropoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to quite large...
which were able to make successful transitions to freshwater and terrestrial environments.
Shell
All chitons bear a row of aragonitic shells, although in some species they are reduced or covered by the girdle tissue.The calcareous valve
Valve (chiton)
Valve is an anatomical term applied to the shell of molluscs. Although in theory any mollusc shell can be termed a "valve", the word is now most commonly applied to members of two classes of molluscs: the Bivalvia and the Polyplacophora , in other words, to those molluscs whose shells are normally...
s that chitons carry dorsally
Dorsum (biology)
In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
are protective, made wholly of aragonite
Aragonite
Aragonite is a carbonate mineral, one of the two common, naturally occurring, crystal forms of calcium carbonate, CaCO3...
, and variously colored, patterned, smooth or sculptured. The shell is divided into eight articulating calcareous
Calcareous
Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...
(aragonite) valve
Valve (chiton)
Valve is an anatomical term applied to the shell of molluscs. Although in theory any mollusc shell can be termed a "valve", the word is now most commonly applied to members of two classes of molluscs: the Bivalvia and the Polyplacophora , in other words, to those molluscs whose shells are normally...
s embedded in the tough muscular girdle that surrounds the chiton's body. This arrangement allows chitons to roll into a protective ball when dislodged and to cling tightly to irregular surfaces.
The front seven plates develop simultaneously, with the rear plate being added later in the developmental process. Growth lines are formed each winter. The inner layer of each of the six intermediate plates is produced anteriorly as an articulating flange. This is called the articulamentum. This inner layer may also be produced laterally in the form of notched insertion plates. These function as an attachment of the valve plates to the soft body. A similar series of insertion plates may be attached to the convex anterior border of the cephalic plate or the convex posterior border of the anal plate.
The sculpture of the valves is one of the taxonomic characteristics, along with the granulation or spinulation of the girdle
After a chiton dies, the individual valves which make up the 8-part shell come apart because the girdle is no longer holding them together, and then the plates sometimes wash up in beach drift. The individual shell plates from a chiton are sometimes known as "butterfly shells" because of their shape.
Girdle ornament
The girdle may be ornamented with scales or spicules which, like the shell plates, are mineralized with aragonite – although a different mineralization process operates in the spicules to in the teeth or shells (implying an independent evolutionary innovation). This process seems quite simple in comparison to other shelly tissue; the crystal structure of the deposited minerals closely resembles the disordered nature of crystals that form inorganically.The protein component of the scales and sclerites is minuscule in comparison with other biomineralized structures, whereas the total proportion of matrix is higher than in mollusc shells. This implies that polysaccharides make up the bulk of the matrix. The girdle spines often bear length-parallel striations.
The wide form of girdle ornament suggests that it serves a secondary role; chitons can survive perfectly well without them. Camouflage or defence are two likely functions.
Internal anatomy
The girdle is often ornamented with spicules, bristles, hairy tufts, spikes, or snake-like scales. The majority of the body is a snailSnail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
-like foot, but no head or other soft-parts beyond the girdle are visible from the dorsal side.
The mantle cavity
Mantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
consists of a narrow channel on each side, lying between the body and the girdle. Water enters the cavity through openings either side of the mouth, then flows along the channel to a second, exhalant, opening close to the anus
Anus
The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...
. Multiple gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s hang down into the mantle cavity along part or all of the lateral pallial groove, each consisting of a central axis with a number of flattened filaments through which oxygen can be absorbed.
The heart has three chambers and is located towards the animal's hind end. Each of the two auricles collects blood from the gills on one side, while the muscular ventricle
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
pumps blood through the aorta
Aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...
and round the body.
The excretory system consists of two nephridia
Nephridium
A Nephridium is an invertebrate organ which occurs in pairs and function similar to kidneys. Nephridia remove metabolic wastes from an animal's body. They are present in many different invertebrate lines. There are two basic types, metanephridia and protonephridia, but there are other...
, which connect to the pericardial cavity
Pericardium
The pericardium is a double-walled sac that contains the heart and the roots of the great vessels.-Layers:...
around the heart, and remove excreta through a pore that opens near the rear of the mantle cavity. The single gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
is located in front of the heart, and releases gametes through a pair of pores just in front of those used for excretion.
Mouth
The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....
is located on the underside of the animal, and contains a tongue-like structure called a radula
Radula
The radula is an anatomical structure that is used by molluscs for feeding, sometimes compared rather inaccurately to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus...
, which has numerous rows of 17 teeth each. The teeth are coated with magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...
, a hard ferric/ferrous oxide mineral. The radula is used to scrape microscopic algae off the substratum. The mouth cavity itself is lined with chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
and is associated with a pair of salivary gland
Salivary gland
The salivary glands in mammals are exocrine glands, glands with ducts, that produce saliva. They also secrete amylase, an enzyme that breaks down starch into maltose...
s. Two sacs open from the back of the mouth, one containing the radula, and the other containing a protrusible sensory subradula organ that is pressed against the substratum to taste for food.
Cilia pull the food through the mouth in a stream of mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
and through the oesophagus, where it is partially digested by enzymes from a pair of large pharyngeal
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
glands. The oesophagus in turn opens into a stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
with where enzymes from a digestive gland complete the breakdown of the food. Nutrients are absorbed through the linings of the stomach and the first part of the intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
. The intestine is divided in two by a sphincter
Sphincter
A sphincter is an anatomical structure, or a circular muscle, that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning...
, with the latter part being highly coiled and functioning to compact the waste matter into faecal pellets. The anus
Anus
The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...
opens just behind the foot.
Chitons lack a clearly demarcated head; their nervous system resembles a dispersed ladder. There are no true ganglia
Ganglion
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....
as there are in other molluscs, although there is a ring of dense neural tissue around the oesophagus. From this ring, nerves branch forwards to innervate the mouth and subradula, while two pairs of main nerve cords run back through the body. One pair, the pedal cords, innervate the foot, while the pallio-visceral cords innervate the mantle and remaining internal organs.
Some species bear an array of tentacles in front of the head.
Senses
The primary sense organs of chitons are the subradula organ and a large number of unique organs called aestheteAesthete (chiton)
Aesthetes are visual organs in chitons. They are tiny 'eyes', too small to be seen unaided, embedded in the organism's shell. They may act in unison to function as a large, dispersed, compound eye. They are light sensing organs that are derived from the mantle of the organism.Some chitons also...
s. The aesthetes consist of light sensitive cells just below the surface of the shell, although they are not capable of true vision. In some cases, however, they are modified to form ocelli, with a cluster of individual photoreceptor cells lying beneath a small lens. An individual chiton may have thousands of such ocelli
There is a relatively good fossil record of chiton shells, but ocelli are only present in those dating to or younger; this would make the ocelli, whose precise function is unclear, the most recent eyes to evolve.
Although chitons lack osphradia
Osphradium
The osphradium is the olfactory organ in certain molluscs, linked with the respiration organ.The main function of this is to test incoming water for silt and other possible food particles.It is used by all members of the Genus Conus....
, statocyst
Statocyst
The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, echinoderms, cephalopods, and crustaceans. A similar structure is also found in Xenoturbella. The statocyst consists of a sac-like structure containing a mineralised mass and numerous...
s, and other sensory organs common to other molluscs, they do have numerous tactile nerve endings, especially on the girdle and within the mantle cavity.
However, chitons lack a cerebral ganglion.
Homing Ability
Several speciesSpecies
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of Chiton are known to exhibit homing behaviours, journeying to feed and then returning to the exact unique spot they previously inhabited. The specific method of how chitons can perform such behaviors has been investigated to some extent, however the reason remains unknown. Suggestions include the chitons remembering the topographic profile of the region, thus being able to guide themselves back to their home scar via a physical knowledge of the rocks and a visual input by their primitive eyes,
The gastropod Nerita textilis is known to deposit mucus as it moves, which a chemoreceptive organ is able to detect and guide the snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
back to its home site, It is unclear if chitons function in this manner. However, it is theorized that they may leave chemical cues along the rock surface and at the home scar which olfactory senses can detect and home in on. Furthermore, old trails may be detected, providing further stimulus for the Chiton to find its home,
Also, chitons have teeth made of magnetite on their radula making them unique among animals. This means they have an exceptionally abrasive tongue with which to scrape food from rocks. These crystals are thought to be involved in magnetoreception, the ability to sense the polarity or the inclination of the Earth's magnetic field, and to be involved in navigation.
Culinary uses
Chitons are eaten in many islands in the Caribbean, including TrinidadTrinidad
Trinidad is the larger and more populous of the two major islands and numerous landforms which make up the island nation of Trinidad and Tobago. It is the southernmost island in the Caribbean and lies just off the northeastern coast of Venezuela. With an area of it is also the fifth largest in...
, Tobago
Tobago
Tobago is the smaller of the two main islands that make up the Republic of Trinidad and Tobago. It is located in the southern Caribbean, northeast of the island of Trinidad and southeast of Grenada. The island lies outside the hurricane belt...
and Barbados
Barbados
Barbados is an island country in the Lesser Antilles. It is in length and as much as in width, amounting to . It is situated in the western area of the North Atlantic and 100 kilometres east of the Windward Islands and the Caribbean Sea; therein, it is about east of the islands of Saint...
. They were also eaten by native Americans of the Pacific coasts of both North and South America. The foot of the chiton is prepared in a manner similar to abalone
Abalone
Abalone , from aulón, are small to very large-sized edible sea snails, marine gastropod molluscs in the family Haliotidae and the genus Haliotis...
.
Life habits
Adhesion
Adhesion is any attraction process between dissimilar molecular species that can potentially bring them in close contact. By contrast, cohesion takes place between similar molecules....
and can cling to rocks very powerfully, like a limpet
Limpet
Limpet is a common name for a number of different kinds of saltwater and freshwater snails ; it is applied to those snails that have a simple shell which is more or less conical in shape, and either is not spirally coiled, or appears not to be coiled in the adult snails.The name limpet is most...
.
Chitons are herbivorous grazers. They eat algae, bryozoans, diatom
Diatom
Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons , fans , zigzags , or stellate colonies . Diatoms are producers within the food chain...
s and sometimes bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
by scraping the rocky substrate with their well-developed radula
Radula
The radula is an anatomical structure that is used by molluscs for feeding, sometimes compared rather inaccurately to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus...
.
A few species of chitons are predatory, such as the small western Pacific species Placiphorella velata. These predatory chitons have an enlarged anterior girdle. They catch other small invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, such as shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
and possibly even small fish, by holding the enlarged, hood-like front end of the girdle up off the surface, and then clamping down on unsuspecting, shelter-seeking prey.
Some chitons exhibit homing behavior, returning to the same spot for the daylight hours and roaming around at night to feed.
Reproduction and life cycle
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
into the water, while the female releases eggs either individually, or in a long string. In most cases, fertilisation takes place either in the surrounding water, or in the mantle cavity of the female. Some species brood the eggs within the mantle cavity, and the species Callistochiton viviparus even retains them within the ovary and gives birth to live young, an example of ovoviviparity
Ovoviviparity
Ovoviviparity, ovovivipary, or ovivipary, is a mode of reproduction in animals in which embryos develop inside eggs that are retained within the mother's body until they are ready to hatch...
.
The eggs have a tough spiny coat, and usually hatch to release a free-swimming trochophore
Trochophore
A trochophore is a type of free-swimming planktonic marine larva with several bands of cilia.By moving their cilia rapidly, a water eddy is created. In this way they control the direction of their movement...
larva, typical of many other mollusc groups. In a few cases, the trochophore remains within the egg (and is then called lecithotrophic – deriving nutrition from yolk), which hatches to produce a miniature adult. Unlike most other molluscs, there is no intermediate stage, or veliger
Veliger
A veliger is the planktonic larva of many kinds of marine and freshwater gastropod molluscs, as well as most bivalve mollusks.- Description :...
, between the trochophore and the adult. Instead, a segmented shell gland forms on one side of the larva, and a foot forms on the opposite side. When the larva is ready to become an adult, the body elongates, and the shell gland secretes the plates of the shell. Unlike the fully grown adult, the larva has a pair of simple eyes, although these may remain for some time in the immature adult.
Predators
Animals which prey on chitons include humans, seagullsGull
Gulls are birds in the family Laridae. They are most closely related to the terns and only distantly related to auks, skimmers, and more distantly to the waders...
, seastars, crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s, lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
and fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
.
The largest species
The largest chiton (up to 33 cm in length) is the brick-red gumboot chitonGumboot chiton
The gumboot chiton, Cryptochiton stelleri, also known as the giant pacific chiton, is the largest of the chitons, growing to 36 cm and over 2000 grams. It is found along the shores of the northern Pacific Ocean from Central California to Alaska, across the Aleutian Islands to the...
of the Pacific Northwest
Pacific Northwest
The Pacific Northwest is a region in northwestern North America, bounded by the Pacific Ocean to the west and, loosely, by the Rocky Mountains on the east. Definitions of the region vary and there is no commonly agreed upon boundary, even among Pacific Northwesterners. A common concept of the...
. In this species the valves are completely internal.
Evolutionary origins
Chitons have a relatively good fossil record, stretching back to the Devonian. Before this, some organisms have been interpreted (tentatively) as stem-group polyplacophora; the record of polyplacophora stretches back to the OrdovicianOrdovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
.
Kimberella
Kimberella is a monospecific genus of bilaterian known only from rocks of the Ediacaran period. The slug-like organism fed by scratching the microbial surface on which it dwelt in a manner similar to the molluscs, although its affinity with this group is contentious.Specimens were first found in...
and Wiwaxia
Wiwaxia
Wiwaxia is a genus of soft-bodied, scale-covered animals known from Burgess shale type Lagerstätte dating from the upper Lower Cambrian to Middle Cambrian. The organisms are mainly known from dispersed sclerites; articulated specimens, where found, range from to a little over 50.8 millimeters in...
of the Precambrian and Cambrian may be related to ancestral polyplacophora. Matthevia
Matthevia
Matthevia is a Cambrian mollusc, perhaps related to the chitons. It consists of repeated monoplacophoran-like shells; according to one hypothesis, chitons arose when these tall shells began to overlap over the generations. The tall element of the shell was retained and forms the tips of modern...
is a Late Cambrian polyplacophoran preserved as individual pointed valves, and sometimes considered to be a chiton, although it can at best be a stem-group member of the group. Based on this and co-occurring fossils, one plausible hypothesis for the origin of polyplacophora has that they formed when an aberrant monoplacophoran was born with multiple centres of calcification, rather than the usual one. Selection quickly acted on the resultant conical shells to form them to overlap into protective armour; their original cones are homologous to the tips of the plates of modern chitons.
The chitons evolved from multiplacophora
Multiplacophora
The multiplacophora are a group of stem-group chitons with a number of plates arranged in 7 rows along the body....
during the palaeozoic, with their relatively conserved modern-day body plan being fixed by the mesozoic.
History of the scientific investigation of chitons
Chitons were first studied by Carolus LinnaeusCarolus Linnaeus
Carl Linnaeus , also known after his ennoblement as , was a Swedish botanist, physician, and zoologist, who laid the foundations for the modern scheme of binomial nomenclature. He is known as the father of modern taxonomy, and is also considered one of the fathers of modern ecology...
in 1758. Since his description of the first four species, chitons have been variously classified. They were called Cyclobranchians ("round arm") in the early 19th century, and then grouped with the aplacophorans in the subphylum
Subphylum
In life, a subphylum is a taxonomic rank intermediate between phylum and superclass. The rank of subdivision in plants and fungi is equivalent to subphylum.Not all phyla are divided into subphyla...
Amphineura in 1876. The class
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
Polyplacophora was named by J. E. Gray in 1821.
Etymology
The English name "chiton" originates from the LatinLatin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
word chitōn, which means "mollusc", and in turn is derived from the Greek word "khitōn", meaning tunic
Tunic
A tunic is any of several types of clothing for the body, of various lengths reaching from the shoulders to somewhere between the hips and the ankles...
(which also is the source of the word chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
). The Greek word "khitōn" can be traced to the Central Semitic word "*kittan", which is from the Akkadian
Akkadian language
Akkadian is an extinct Semitic language that was spoken in ancient Mesopotamia. The earliest attested Semitic language, it used the cuneiform writing system derived ultimately from ancient Sumerian, an unrelated language isolate...
words "kitû" or "kita’um", meaning flax or linen, and originally the Sumerian
Sumerian language
Sumerian is the language of ancient Sumer, which was spoken in southern Mesopotamia since at least the 4th millennium BC. During the 3rd millennium BC, there developed a very intimate cultural symbiosis between the Sumerians and the Akkadians, which included widespread bilingualism...
word "gada" or "gida".
The Greek-derived name Polyplacophora comes from the words poly- (many), plako- (tablet), and -phoros (bearing), a reference to the chiton's eight shell plates.
Taxonomy
Most classification schemes in use today are based, at least in part, on Pilsbry's Manual of Conchology (1892–1894), extended and revised by Kaas and Van Belle (1985–1990).Since chitons were first described by Linnaeus (1758) there have been extensive taxonomic studies at the species level. However, the taxonomic classification at higher levels in the group has remained somewhat unsettled.
The most recent classification (Sirenko 2006) is based not only on shell morphology, as usual, but also other important features including aesthete
Aesthete (chiton)
Aesthetes are visual organs in chitons. They are tiny 'eyes', too small to be seen unaided, embedded in the organism's shell. They may act in unison to function as a large, dispersed, compound eye. They are light sensing organs that are derived from the mantle of the organism.Some chitons also...
s, girdle, radula, gills, glands, egg hull projections and spermatozoids. It includes all the living and extinct genera of chitons.
This system is now generally accepted.
- Class Polyplacophora Gray, 1821
- Subclass PaleoloricataPaleoloricataThe Paleoloricata are valved polyplacophora without sutural laminae or insertion plates . The "order" probably represents a paraphyletic grouping....
Bergenhayn, 1955- Order Chelodida Bergenhayn, 1943
-
- Family ChelodidaeChelodidaeChelodidae is an extinct of polyplacophoran mollusc....
Bergenhayn, 1943- ChelodesChelodesChelodes is a genus of Palaeozoic mollusc made up of serially repeated monoplacophoran-like valves....
Davidson et King, 1874 - Euchelodes Marek, 1962
- CalceochitonCalceochitonCalceochiton is an extinct of polyplacophoran mollusc. Calceochiton became extinct during the Ordovician period....
Flower, 1968
- Chelodes
- Family Chelodidae
-
- Order Septemchitonida Bergenhayn, 1955
-
- Family Gotlandochitonidae Bergenhayn, 1955
- GotlandochitonGotlandochitonGotlandochiton is an extinct of polyplacophoran mollusc. Gotlandochiton became extinct during the Silurian period....
Bergenhayn, 1955
- Gotlandochiton
- Family Helminthochitonidae Van Belle, 1975
- KindbladochitonKindbladochitonKindbladochiton is an extinct of polyplacophoran mollusc. Kindbladochiton became extinct during the Ordovician period....
Van Belle, 1975 - Diadelochiton Hoare, 2000
- HelminthochitonHelminthochitonHelminthochiton is an extinct of polyplacophoran mollusc. Helminthochiton became extinct during the Permian period....
Salter in Griffith et M'Coy, 1846 - EchinochitonEchinochitonEchinochiton is an Ordovician chiton with hollow spines on its margins; these spines, which are unique among the chitons, have a strong organic component and show growth lines....
Pojeta, Eernisse, Hoare et Henderson, 2003
- Kindbladochiton
- Family Septemchitonidae Bergenhayn, 1955
- SeptemchitonSeptemchitonSeptemchiton is an extinct of polyplacophoran mollusc. Septemchiton became extinct during the Ordovician period....
Bergenhayn, 1955 - PaleochitonPaleochitonPaleochiton is an extinct of polyplacophoran mollusc....
A. G. Smith, 1964 - Thairoplax Cherns, 1998
- Septemchiton
- Family Gotlandochitonidae Bergenhayn, 1955
-
- Order Chelodida Bergenhayn, 1943
- Subclass LoricataLoricataLoricata is a group of reptiles that includes crocodylians and their ancestors. It was named by German naturalist Blasius Merrem in his 1820 Versuch eines Systems der Amphibien. Merrem considered it to be one of three groups of Pholidota , the other two being Testudinata and Squamata...
Shumacher, 1817- Order Lepidopleurida Thiele, 1910
- Suborder Cymatochitonina Sirenko et Starobogatov, 1977
- Family Acutichitonidae Hoare, Mapes et Atwater, 1983
- AcutichitonAcutichitonAcutichiton is an extinct of polyplacophoran mollusc. Acutichiton became extinct during the Carboniferous period....
Hoare, Sturgeon et Hoare, 1972 - Elachychiton Hoare, Sturgeon et Hoare, 1972
- Harpidochiton Hoare et Cook, 2000
- Arcochiton Hoare, Sturgeon et Hoare, 1972
- Kraterochiton Hoare, 2000
- Soleachiton Hoare, Sturgeon et Hoare, 1972
- Asketochiton Hoare et Sabattini, 2000
- Acutichiton
- Family Cymatochitonidae Sirenko et Starobogatov, 1977
- CymatochitonCymatochitonCymatochiton is an extinct of polyplacophoran mollusc. Cymatochiton became extinct during the Permian period....
DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1882 - Compsochiton Hoare et Cook, 2000
- Cymatochiton
- Family Gryphochitonidae PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1900- Gryphochiton Gray, 1847
- Family Lekiskochitonidae Smith et Hoare, 1987
- Lekiskochiton Hoare et Smith, 1984
- Family Permochitonidae Sirenko et Starobogatov, 1977
- PermochitonPermochitonPermochiton is an extinct of polyplacophoran mollusc. Permochiton became extinct during the Permian period....
IredaleTom IredaleTom Iredale was an English-born ornithologist and malacologist who had a long association with Australia, where he lived for most of his life. He was an autodidact who never went to university and lacked formal training...
et Hull, 1926
- Permochiton
- Family Acutichitonidae Hoare, Mapes et Atwater, 1983
- Suborder LepidopleurinaLepidopleurinaLepidopleurina is an extinct of polyplacophoran mollusc....
Thiele, 1910- Family Ferreiraellidae Dell’ Angelo et Palazzi, 1991
- GlaphurochitonGlaphurochitonGlaphurochiton is a genus of fossil chiton known from the Mazon Creek biota. Remarkably, it contains an intact radula, which with 17 teeth per row and over 100 rows is almost identical to the radula of modern chitons . The radula extends from the first to third shell plates....
Raymond, 1910 - ?Pyknochiton Hoare, 2000
- ?Hadrochiton Hoare, 2000
- Ferreiraella Sirenko, 1988
- Glaphurochiton
- Family Glyptochitonidae Starobogatov et Sirenko, 1975
- GlyptochitonGlyptochitonGlyptochiton is an extinct of polyplacophoran mollusc. Glyptochiton became extinct during the Carboniferous period....
Konninck, 1883
- Glyptochiton
- Family LeptochitonidaeLeptochitonidaeLeptochitonidae is an extinct of polyplacophoran mollusc....
DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1889- Colapterochiton Hoare et Mapes, 1985
- Coryssochiton DeBrock, Hoare et Mapes, 1984
- Proleptochiton Sirenko et Starobogatov, 1977
- Schematochiton Hoare, 2002
- PterochitonPterochitonPterochiton is an extinct of polyplacophoran mollusc....
(CarpenterPhillip Pearsall CarpenterPhilip Pearsall Carpenter Rev. Dr. , who in 1841, was ordained Presbyterian minister in England, and a Doctorate of Philosophy in 1860, and whose field work as a malacologist or conchologist in North America is still well regarded today...
MS) DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1882 - LeptochitonLeptochitonLeptochiton is an extinct of polyplacophoran mollusc. Leptochiton became extinct during the Pliocene period....
Gray, 1847 - ParachitonParachitonParachiton is an extinct of polyplacophoran mollusc....
Thiele, 1909 - Terenochiton IredaleTom IredaleTom Iredale was an English-born ornithologist and malacologist who had a long association with Australia, where he lived for most of his life. He was an autodidact who never went to university and lacked formal training...
, 1914 - TrachypleuraTrachypleuraTrachypleura is an extinct of polyplacophoran mollusc. Trachypleura became extinct during the Triassic period....
Jaeckel, 1900 - Pseudoischnochiton Ashby, 1930
- LepidopleurusLepidopleurusLepidopleurus is a genus of chitons in the family Leptochitonidae.- Species:* Lepidopleurus cajetanus * Lepidopleurus fairchildi Iredale & Hull, 1929* Lepidopleurus finlayi...
Risso, 1826 - Hanleyella Sirenko, 1973
- Family Camptochitonidae Sirenko, 1997
- Camptochiton DeBrock, Hoare et Mapes, 1984
- Pedanochiton DeBrock, Hoare et Mapes, 1984
- Euleptochiton Hoare et Mapes, 1985
- Pileochiton DeBrock, Hoare et Mapes, 1984
- Chauliochiton Hoare et Smith, 1984
- Stegochiton Hoare et Smith, 1984
- Family Nierstraszellidae Sirenko, 1992
- Nierstraszella Sirenko, 1992
- Family Mesochitonidae Dell’ Angelo et Palazzi, 1989
- MesochitonMesochitonMesochiton is an extinct of polyplacophoran mollusc. Mosochiton became extinct during the Jurassic period....
Van Belle, 1975 - PterygochitonPterygochitonPterygochiton is an extinct of polyplacophoran mollusc. Pterygochiton became extinct during the Carboniferous period....
Rochebrune, 1883
- Mesochiton
- Family Protochitonidae Ashby, 1925
- ProtochitonProtochitonProtochiton is an extinct of polyplacophoran mollusc. Protochiton became extinct during the Eocene period....
Ashby, 1925 - Deshayesiella (CarpenterPhillip Pearsall CarpenterPhilip Pearsall Carpenter Rev. Dr. , who in 1841, was ordained Presbyterian minister in England, and a Doctorate of Philosophy in 1860, and whose field work as a malacologist or conchologist in North America is still well regarded today...
MS) DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1879 - Oldroydia DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1894
- Protochiton
- Family Hanleyidae Bergenhayn, 1955
- HanleyaHanleyaHanleya is a genus of polyplacophoran mollusc known from Oligocene and Miocene fossils; it is represented today by a number of species including H. sinica Xu 1990 , H. brachyplax and H. hanleyi Bean in Thorpe, 1844 , which feeds on sponges....
Gray, 1857 - Hemiarthrum DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1876
- Hanleya
- Family Ferreiraellidae Dell’ Angelo et Palazzi, 1991
- Suborder Cymatochitonina Sirenko et Starobogatov, 1977
- Order ChitonidaChitonidaChitonida is an order of chitons.-Taxonomy:* Suborder Chitonina Thiele, 1910* Superfamily Chitonoidea Rafinesque, 1815** Family Ochmazochitonidae Hoare et Smith, 1984*** Ochmazochiton Hoare et Smith, 1984** Family Ischnochitonidae Dall, 1889...
Thiele, 1910- Suborder ChitoninaChitoninaChitonina is an extinct of polyplacophoran mollusc....
Thiele, 1910 - Superfamily Chitonoidea Rafinesque, 1815
- Family Ochmazochitonidae Hoare et Smith, 1984
- Ochmazochiton Hoare et Smith, 1984
- Family IschnochitonidaeIschnochitonidaeIschnochitonidae is an extinct of polyplacophoran mollusc....
DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1889- IschnochitonIschnochitonIschnochiton is a genus of polyplacophoran mollusc.-Species:* Ischnochiton abyssicola * Ischnochiton alascensis Thiele, 1910* Ischnochiton albus * Ischnochiton circumvallatus...
Gray, 1847 - Stenochiton H. Adams et Angas, 1864
- StenoplaxStenoplaxStenoplax is of polyplacophoran mollusc ....
(Carpenter MSPhillip Pearsall CarpenterPhilip Pearsall Carpenter Rev. Dr. , who in 1841, was ordained Presbyterian minister in England, and a Doctorate of Philosophy in 1860, and whose field work as a malacologist or conchologist in North America is still well regarded today...
) DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1879 - Lepidozona PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1892 - Stenosemus Middendorff, 1847
- Subterenochiton IredaleTom IredaleTom Iredale was an English-born ornithologist and malacologist who had a long association with Australia, where he lived for most of his life. He was an autodidact who never went to university and lacked formal training...
et Hull, 1924 - Thermochiton Saito et Okutani, 1990
- Connexochiton Kaas, 1979
- Tonicina Thiele, 1906
- Ischnochiton
- Family Callistoplacidae PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1893- Ischnoplax DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1879 - CallistochitonCallistochitonCallistochiton is an extinct of polyplacophoran mollusc. Callistochiton became extinct during the Pliocene period....
CarpenterPhillip Pearsall CarpenterPhilip Pearsall Carpenter Rev. Dr. , who in 1841, was ordained Presbyterian minister in England, and a Doctorate of Philosophy in 1860, and whose field work as a malacologist or conchologist in North America is still well regarded today...
MS, DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1879 - Callistoplax DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1882 - Ceratozona DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1882 - Calloplax Thiele, 1909
- Ischnoplax Dall
- Family ChaetopleuridaeChaetopleuridaeChaetopleuridae is a family of chitons. They are marine molluscs.-Genera:Two genera are known in this family:* Chaetopleura Shuttleworth, 1853* Dinoplax Carpenter MS, Dall, 1882...
Plate, 1899- ChaetopleuraChaetopleuraChaetopleura is a genus of chitons in the family Chaetopleuridae. They are marine molluscs.-Species:The genus has been separated into two subgenera.subgenus Chaetopleura * Chaetopleura angolensis Thiele, 1909...
Shuttleworth, 1853 - DinoplaxDinoplaxDinoplax is a genus of chitons in the family Chaetopleuridae. They are marine molluscs.-Taxonomy:Species in this genus include:* Dinoplax chelazziana * Dinoplax fossus Sykes, 1899* Dinoplax gigas...
Carpenter MS, DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1882
- Chaetopleura
- Family Loricidae IredaleTom IredaleTom Iredale was an English-born ornithologist and malacologist who had a long association with Australia, where he lived for most of his life. He was an autodidact who never went to university and lacked formal training...
et Hull, 1923- LoricaLorica (genus)Lorica is a genus of chitons in the family Schizochitonidae.- Extinct representatives :Extinct representatives of the genus are known from the Cretaceous of America and the Eocene & Miocene of Oceania....
H. et A. Adams, 1852 - LoricellaLoricella (chiton)Loricella is a genus of chitons in the family Schizochitonidae. They are marine molluscs. .-Taxonomy:Species in the genus include:* Loricella angasi Loricella is a genus of chitons in the family Schizochitonidae. They are marine molluscs. .-Taxonomy:Species in the genus include:* Loricella angasi...
PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1893 - OochitonOochitonOochiton is an extinct of polyplacophoran mollusc. Oochiton became extinct during the Miocene period....
Ashby, 1929
- Lorica
- Family Callochitonidae Plate, 1901
- CallochitonCallochitonCallochiton is a genus of chitons in the family Callochitonidae.-Species:* Callochiton castaneus * Callochiton crocinus * Callochiton empleurus * Callochiton kapitiensis Mestayer, 1926...
Gray, 1847 - Eudoxochiton Shuttleworth, 1853
- Vermichiton Kaas, 1979
- Callochiton
- Family ChitonidaeChitonidaeChitonidae is a family of chitons or polyplacophorans, marine mollusks whose shell is composed of eight articulating plates or valves. There are fifteen extant genera in three subfamilies.-Subfamilies and genera:...
Rafinesque, 1815- Subfamily Chitoninae Rafinesque, 1815
- ChitonChiton (genus)Chiton is a genus of chiton, a polyplacophoran mollusk in the family Chitonidae.-Taxonomy:The genus Chiton has been split into several subgenera as follows:* Subgenus Chiton Linnaeus, 1758...
Linnaeus, 1758 - Amaurochiton Thiele, 1893
- Radsia Gray, 1847
- SypharochitonSypharochitonSypharochiton is a genus of chitons in the family Chitonidae.-Species:* Sypharochiton pelliserpentis * Sypharochiton aorangi * Sypharochiton sinclairi...
Thiele, 1893 - Nodiplax Beu, 1967
- RhyssoplaxRhyssoplaxRhyssoplax is a genus of chitons in the family Chitonidae, endemic to Australia, New Zealand, New Caledonia, Norfolk Island, and the Kermadec Islands.-Species:* Rhyssoplax aerea aerea...
Thiele, 1893 - Teguloaplax IredaleTom IredaleTom Iredale was an English-born ornithologist and malacologist who had a long association with Australia, where he lived for most of his life. He was an autodidact who never went to university and lacked formal training...
& Hull, 1926 - Mucrosquama IredaleTom IredaleTom Iredale was an English-born ornithologist and malacologist who had a long association with Australia, where he lived for most of his life. He was an autodidact who never went to university and lacked formal training...
, 1893 - Subfamily Toniciinae PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1893 - Tonicia Gray, 1847
- OnithochitonOnithochitonOnithochiton is a genus of chitons in the family Chitonidae, which is distributed from Australia and New Zealand to South Africa.-Species:* Onithochiton ashbyi* Onithochiton discrepans* Onithochiton gotoi* Onithochiton helenae...
Gray, 1847 - Subfamily Acanthopleurinae DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1889 - AcanthopleuraAcanthopleuraAcanthopleura is a genus of chitons in the family Chitonidae. In this genus the girdle is spiny or spiky. It has eight described species at present.-Species:...
Guilding, 1829 - Liolophura PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1893 - Enoplochiton Gray, 1847
- Squamopleura Nierstrasz, 1905
- Superfamily Schizochitonoidea DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1889 - Family SchizochitonidaeSchizochitonidaeSchizochitonidae is an extinct of polyplacophoran mollusc....
DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1889- Incissiochiton Van Belle, 1985
- SchizochitonSchizochitonSchizochiton is an extinct of polyplacophoran mollusc. Schizochiton became extinct during the Miocene period....
Gray, 1847
- Family Ochmazochitonidae Hoare et Smith, 1984
- Suborder AcanthochitoninaAcanthochitoninaAcanthochitonina is an extinct of polyplacophoran mollusc....
Bergenhayn, 1930- Superfamily Mopalioidea DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1889 - Family Tonicellidae Simroth, 1894
- Subfamily Tonicellinae Simroth, 1894
- LepidochitonaLepidochitonaLepidochitona is a genus of chiton; L. raymondi is the only hermaphroditic polyplacophoran....
Gray, 1821 - Particulazona Kaas, 1993
- Boreochiton Sars, 1878
- TonicellaTonicellaTonicella is a genus of chitons known as the lined chitons. The genus name derives from the Greek tonos and cell .-Species:Species within the genus Tonicella include:...
CarpenterPhillip Pearsall CarpenterPhilip Pearsall Carpenter Rev. Dr. , who in 1841, was ordained Presbyterian minister in England, and a Doctorate of Philosophy in 1860, and whose field work as a malacologist or conchologist in North America is still well regarded today...
, 1873 - Nuttallina (CarpenterPhillip Pearsall CarpenterPhilip Pearsall Carpenter Rev. Dr. , who in 1841, was ordained Presbyterian minister in England, and a Doctorate of Philosophy in 1860, and whose field work as a malacologist or conchologist in North America is still well regarded today...
MS) Dall, 1871 - SpongioradsiaSpongioradsiaSpongioradsia is an extinct of polyplacophoran mollusc. Spongioradsia became extinct during the Oligocene period....
PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1894 - Oligochiton Berry, 1922
- Lepidochitona
- Subfamily Juvenichitoninae Sirenko, 1975
- Juvenichiton Sirenko, 1975
- Micichiton Sirenko, 1975
- Nanichiton Sirenko, 1975
- Family Schizoplacidae Bergenhayn, 1955
- Schizoplax DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1878
- Schizoplax Dall
- Family MopaliidaeMopaliidaeMopaliidae is an extinct of polyplacophoran mollusc....
DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1889 - Subfamily Heterochitoninae Van Belle, 1978
- HeterochitonHeterochitonHeterochiton is an extinct of polyplacophoran mollusc. Heterochiton became extinct during the Jurassic period....
Fucini, 1912 - AllochitonAllochitonAllochiton is an extinct of polyplacophoran mollusc. Allochiton became extinct during the Jurassic period....
Fucini, 1912
- Heterochiton
- Subfamily Mopaliinae DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1889- AerilammaAerilammaAerilamma is a genus of chitons in the family Mopaliidae.-References:* Powell A. W. B., New Zealand Mollusca, William Collins Publishers Ltd, Auckland, New Zealand 1979 ISBN 0-00-216906-1...
Hull, 1924 - GuildingiaGuildingiaGuildingia is a genus of chitons in the family Mopaliidae.-References:* * Powell A. W. B., New Zealand Mollusca, William Collins Publishers Ltd, Auckland, New Zealand 1979 ISBN 0-00-216906-1...
PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1893 - Frembleya H. Adams, 1866
- DiaphoroplaxDiaphoroplaxDiaphoroplax is a genus of chitons in the family Mopaliidae.-References:* Powell A. W. B., New Zealand Mollusca, William Collins Publishers Ltd, Auckland, New Zealand 1979 ISBN 0-00-216906-1...
IredaleTom IredaleTom Iredale was an English-born ornithologist and malacologist who had a long association with Australia, where he lived for most of his life. He was an autodidact who never went to university and lacked formal training...
, 1914 - PlaxiphoraPlaxiphoraPlaxiphora is a genus of chitons in the family Mopaliidae.-Species:* Plaxiphora albida* Plaxiphora atlantica* Plaxiphora aurata campbelli Filhol, 1880* Plaxiphora aurata* Plaxiphora aurata * Plaxiphora aurea...
Gray, 1847 - Placiphorina Kaas & Van Belle, 1994
- NuttallochitonNuttallochitonNuttallochiton is a genus of chiton; the only one to have paired rather than fused gonads....
Plate, 1899 - MopaliaMopalia- Species :*Mopalia mucosa*Mopalia ciliata*Mopalia lignosa*Mopalia spectabilis*Mopalia hindsii...
Gray, 1847 - MaorichitonMaorichitonMaorichiton is a genus of chitons in the family Mopaliidae.-Species:Species within this genus include:* Maorichiton caelatus * Maorichiton schauinslandi -References:...
IredaleTom IredaleTom Iredale was an English-born ornithologist and malacologist who had a long association with Australia, where he lived for most of his life. He was an autodidact who never went to university and lacked formal training...
, 1914 - PlaciphorellaPlaciphorellaPlaciphorella, the veiled chiton, is a polyplacophoran mollusc with precephalic tentacles, which are used in feeding....
(CarpenterPhillip Pearsall CarpenterPhilip Pearsall Carpenter Rev. Dr. , who in 1841, was ordained Presbyterian minister in England, and a Doctorate of Philosophy in 1860, and whose field work as a malacologist or conchologist in North America is still well regarded today...
MS) DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1879 - Katharina Gray, 1847
- Amicula Gray, 1847
- Aerilamma
- Superfamily Cryptoplacoidea H. et A. Adams, 1858
- Family AcanthochitonidaeAcanthochitonidaeAcanthochitonidae is a family of chitons.-Description:These small to large chitons are characterised by a broad girdle with erect tufts of up to ten large bristles. The coarsely granular valves of the shell are partially overlapped by the girdle. This girdle is all covered by coarse spines. The...
PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1893 - Subfamily Acanthochitoninae PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1893- AcanthochitonaAcanthochitonaAcanthochitona is a genus of chitons in the family Acanthochitonidae, of worldwide distribution.-Species:According to the World Register of Marine Species , species in the genus Acanthopleura include...
Gray, 1921 - CraspedochitonCraspedochitonCraspedochiton is a genus of chitons in the family Acanthochitonidae, endemic to New Zealand, the Philippines and Australia.-Species:* Craspedochiton cornutus * Craspedochiton elegans * Craspedochiton hemphilli...
Shuttleworth, 1853 - Spongiochiton (CarpenterPhillip Pearsall CarpenterPhilip Pearsall Carpenter Rev. Dr. , who in 1841, was ordained Presbyterian minister in England, and a Doctorate of Philosophy in 1860, and whose field work as a malacologist or conchologist in North America is still well regarded today...
MS) DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1882 - NotoplaxNotoplaxNotoplax is a genus of chitons in the family Acanthochitonidae.-Species:* Notoplax addenda Iredale & Hull, 1925* Notoplax aenigma * Notoplax aqabaensis* Notoplax arabica Kaas & Van Belle, 1988...
H. Adams, 1861 - Pseudotonicia Ashby, 1928
- Bassethullia PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1928 - Americhiton Watters, 1990
- Choneplax (CarpenterPhillip Pearsall CarpenterPhilip Pearsall Carpenter Rev. Dr. , who in 1841, was ordained Presbyterian minister in England, and a Doctorate of Philosophy in 1860, and whose field work as a malacologist or conchologist in North America is still well regarded today...
MS) DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1882 - CryptoconchusCryptoconchusCryptoconchus is a genus of chitons in the family Acanthochitonidae.- C. porosus :Cryptoconchus porosus, common name the butterfly chiton, is a large chiton with the following synonyms:...
(de Blainville MS) Burrow, 1815
- Acanthochitona
- Subfamily Cryptochitoninae PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1893- Cryptochiton Middendorff, 1847
- Family Hemiarthridae Sirenko, 1997
- Hemiarthrum CarpenterPhillip Pearsall CarpenterPhilip Pearsall Carpenter Rev. Dr. , who in 1841, was ordained Presbyterian minister in England, and a Doctorate of Philosophy in 1860, and whose field work as a malacologist or conchologist in North America is still well regarded today...
in DallW. H. DallWilliam Healey Dall was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska...
, 1876 - Weedingia Kaas, 1988
- Hemiarthrum Carpenter
- Family Choriplacidae Ashby, 1928
- Choriplax PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1894
- Choriplax Pilsbry
- Family Cryptoplacidae H. et A. Adams, 1858
- CryptoplaxCryptoplaxCryptoplax is an extinct of polyplacophoran mollusc. Crytoplax became extinct during the Pliocene period....
de Blainville, 1818
- Cryptoplax
- Superfamily Mopalioidea Dall
- Suborder Chitonina
- Order Lepidopleurida Thiele, 1910
- Incertae sedisIncertae sedis, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
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- Family ScanochitonidaeScanochitonidaeScanchitonidae is an extinct of polyplacophoran mollusc....
Bergenhayn, 1955- ScanochitonScanochitonScanochiton is an extinct of polyplacophoran mollusc. Scanochiton became extinct during the Cretaceous period....
Bergenhayn, 1955
- Scanochiton
- Family Olingechitonidae Starobogatov et Sirenko, 1977
- OlingechitonOlingechitonOlingechiton is an extinct of polyplacophoran mollusc. Olingechiton became extinct at the end of the Cretaceous period....
Bergenhayn, 1943
- Olingechiton
- Family Haeggochitonidae Sirenko et Starobogatov, 1977
- HaeggochitonHaeggochitonHaeggochiton is an extinct of polyplacophoran mollusc known from a single occurrence in the Cretaceous of Europe....
Bergenhayn, 1955
- Haeggochiton
- Family Ivoechitonidae Sirenko et Starobogatov, 1977
- IvoechitonIvoechitonIvoechiton is an extinct of polyplacophoran mollusc. Ivoechiton became extinct during the Cretaceous period....
Bergenhayn, 1955
- Ivoechiton
- Family Scanochitonidae
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- Subclass Paleoloricata