Crustacean larvae
Encyclopedia
Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult
, in which the hard exoskeleton
is shed to allow the animal to grow. The larva
e of crustacean
s often bear little resemblance to the adult, and there are still cases where it is not known what larvae will grow into what adults. This is especially true of crustaceans which live as benthic adults (on the sea bed), but where the larvae are plankton
ic and therefore more easily caught.
Many crustacean larvae were not immediately recognised as larvae when they were discovered, and were described as new genera and species. The names of these genera have become generalised to cover specific larval stages across wide groups of crustaceans, such as zoea and nauplius. Other terms described forms which are only found in particular groups, such as the glaucothoe of hermit crab
s, or the phyllosoma
of slipper lobster
s and spiny lobster
s.
, which is usually fertilised
, but may instead be produced by parthenogenesis
. This egg hatches into a pre-larva or pre-zoea. Through a series of moults, the young animal then passes through various zoea stages, followed by a megalopa or post-larva. This is followed by metamorphosis
into an immature form, which broadly resembles the adult, and after further moults, the adult form is finally reached. Some crustaceans continue to moult as adults, while for others, the development of gonad
s signals the final moult.
Any organs which are absent from the adults do not generally appear in the larvae, although there are a few exceptions, such as the vestige of the fourth pereiopod in the larvae of Lucifer
, and some pleopods in certain Anomura
and crab
s.
hatching in 1699. Despite this, and other observations over the following decades, there was controversy among scientists about whether or not metamorphosis
occurred in crustaceans, with conflicting observations presented, based on different species, some of which went through a metamorphosis, and some of which did not. This controversy persisted until the 1840s, and the first descriptions of a complete series of larval forms were not published until the 1870s (Sidney Irving Smith
on the American lobster
in 1873; Georg Ossian Sars on the European lobster
in 1875, and Walter Faxon
on the shrimp Palaemonetes vulgaris
in 1879).
in 1785 for animals now known to be the larvae of copepod
s. The nauplius stage (plural: nauplii) is characterised by the use of the appendage
s of the head (the antennae
) for swimming. The nauplius is also the stage at which a simple, unpaired eye first appears. The eye is known for that reason as the "naupliar eye", and is often absent in later developmental stages, although it is retained into the adult form in some groups, such as the Notostraca
.
in 1802 for an animal now known to be the larva of a crab
. The zoea stage (plural: zoeas or zoeae) is characterised by the use of the thoracic
appendages for swimming.
erected the genus Megalopa in 1813 for a post-larval crab; a shrimp
post-larva is called a parva; hermit crab
post-larva are called glaucothoe.
, and this difference in the larvae is thought to reflect "a fundamental cleavage" of the crustaceans.
horseshoe shrimp
Lightiella magdalenina, the young experience 15 metanaupliar stages and 2 juvenile stages, with each of the first six stages adding 2 trunk segments, and the last four segments being added singly.
are lecithotrophic, consuming egg yolk
rather than using external food sources. This characteristic, which is shared with malacostracan groups such as the Decapoda and Euphausiacea (krill) has been used to suggest a link between Remipedia and Malacostraca.
Young isopod
crustaceans hatch directly into a manca stage, which is similar in appearance to the adult. The lack of a free-swimming larval form has led to high rates of endemism in isopods, but has also allowed them to colonise the land, in the form of the woodlice
.
are poorly known. In the superfamily Lysiosquilloidea, the larvae hatch as antizoea larvae, with five pairs of thoracic appendages, and develop into erichthus larvae, where the pleopods appear. In the Squilloidea, a pseudozoea larva develops into an alima larva, while in Gonodactyloidea, a pseudozoea develops into an erichthus.
A single fossil
stomatopod larva has been discovered, in the Upper Jurassic Solnhofen
lithographic limestone
.
. During the furcilia stages, segments with pairs of swimmerets are added, beginning at the frontmost segments, with each new pair only becoming functional at the next moult. After the final furcilia stage, the krill resembles the adult.
s of the suborder Dendrobranchiata, all decapod crustaceans brood their eggs on the female's pleopods. This has resulted in development in decapod crustaceans being generally abbreviated. There are at most 9 larval stages in decapods, as in krill
, and both decapod nauplii and krill nauplii often lack mouthparts and survive on nutrients supplied in the egg yolk
(lecithotrophy). In species with normal development, eggs are roughly 1% of the size of the adult; in species with abbreviated development, and therefore more yolk in the eggs, the eggs may reach 1/9 of the adult's size.
The post-larva of shrimp
is called parva, after the species Acanthephyra parva described by Henri Coutière, but which was later recognised as the larva of Acanthephyra purpurea.
In the marine lobster
s, there are three larval stages, all similar in appearance.
Freshwater
crayfish
embryo
s differ from those of other crustaceans in having 40 ectoteloblast cells, rather than around 19. The larvae show abbreviated development, and hatch with a full complement of adult appendages with the exceptions of the uropods and the first pair of pleopods.
The larvae of the Achelata
(slipper lobster
s and spiny lobster
s) are unlike any other crustacean larvae. The larvae are known as phyllosoma, after the genus Phyllosoma erected by William Elford Leach
in 1817. They are flattened and transparent, with long legs and eyes on long eyestalks. After passing through 8–10 phyllosoma stages, the larva undergoes "the most profound transformation at a single moult in the Decapoda", when it develops into the so-called puerulus stage, which is an immature form resembling the adult animal.
The members of the traditional infraorder Thalassinidea
can be divided into two groups on the basis of their larvae. According to Robert Gurney
, the "homarine group" comprises the families Axiidae
and Callianassidae
, while the "anomuran group" comprises the families Laomediidae and Upogebiidae
. This split corresponds with the division later confirmed with molecular phylogenetics.
Among the Anomura
, there is considerable variation in the number of larval stages. In the South America
n freshwater
genus Aegla, the young hatch from the eggs in the adult form. Squat lobster
s pass through four, or occasionally five, larval states, which have a long rostrum
, and a spine on either side of the carapace
; the first post-larva closely resembles the adult. Porcelain crab
s have two or three larval stages, in which the rostrum and the posterior spine on the carapace are "enormously long". Hermit crab
s pass through around four larval stages. The post-larva is known as the glaucothoe, after a genus named by Henri Milne-Edwards
in 1830. The glaucothoe is 3 millimetre (0.118110236220472 in) long in Pagurus longicarpus
, but glaucothoe larvae up to 20 mm (0.78740157480315 in) are known, and were once thought to represent animals which had failed to develop correctly. Like the preceding stages, the glaucothoe is symmetrical, and although the glaucothoe begins as a free-swimming form, it often acquires a gastropod shell
to live in; the coconut crab
, Birgus latro, always carries a shell when the immature animal comes ashore, but this is discarded later.
Although they are classified as crab
s, the larvae of Dromiacea
are similar to those of the Anomura, which led many scientists to place dromiacean crabs in the Anomura, rather than with the other crabs. Apart from the Dromiacea, all crabs share a similar and distinctive larval form. The crab zoea has a slender, curved abdomen
and a forked telson
, but its most striking features are the long rostral and dorsal spines, sometimes augmented by further, lateral spines. These spines can be many times longer than the body of the larva. Crab prezoea larvae have been found fossil
ised in the stomach
contents of the Early Cretaceous
bony fish
Tharrhias
.
s have six naupliar stages, followed by a stage called the copepodid, which has the same number of body segments and appendages in all copepods. The copepodid larva has two pairs of unsegmented swimming appendages, and an unsegmented "hind-body" comprising the thorax and the abdomen. There are typically five copepodid stages, but parasitic copepods may stop after a single copepodid stage. Once the gonads develop, there are no further moults.
, Hansenocaris, is only known from its larvae. They were first described by Christian Andreas Victor Hensen
in 1887, and named "y-nauplia" by Hans Jacob Hansen
, assuming them to be the larvae of barnacle
s. The adults are presumed to be parasites
of other animals.
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
, in which the hard exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
is shed to allow the animal to grow. The larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e of crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s often bear little resemblance to the adult, and there are still cases where it is not known what larvae will grow into what adults. This is especially true of crustaceans which live as benthic adults (on the sea bed), but where the larvae are plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
ic and therefore more easily caught.
Many crustacean larvae were not immediately recognised as larvae when they were discovered, and were described as new genera and species. The names of these genera have become generalised to cover specific larval stages across wide groups of crustaceans, such as zoea and nauplius. Other terms described forms which are only found in particular groups, such as the glaucothoe of hermit crab
Hermit crab
Hermit crabs are decapod crustaceans of the superfamily Paguroidea. Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell that is carried around by the hermit crab.-Description:...
s, or the phyllosoma
Phyllosoma
The phyllosoma is the larval stage of spiny, slipper and coral lobsters , and represents one of the most significant characteristics that unify them into the taxon Achelata...
of slipper lobster
Slipper lobster
Slipper lobsters are a family of decapod crustaceans found in all warm oceans and seas. Despite their name, they are not true lobsters, but are more closely related to spiny lobsters and furry lobsters. Slipper lobsters are instantly recognisable by their enlarged antennae, which project forward...
s and spiny lobster
Spiny lobster
Spiny lobsters, also known as langouste or rock lobsters, are a family of about 45 species of achelate crustaceans, in the Decapoda Reptantia...
s.
Life cycle
At its most complete, a crustacean's life cycle begins with an eggEgg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
, which is usually fertilised
Fertilisation
Fertilisation is the fusion of gametes to produce a new organism. In animals, the process involves the fusion of an ovum with a sperm, which eventually leads to the development of an embryo...
, but may instead be produced by parthenogenesis
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...
. This egg hatches into a pre-larva or pre-zoea. Through a series of moults, the young animal then passes through various zoea stages, followed by a megalopa or post-larva. This is followed by metamorphosis
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
into an immature form, which broadly resembles the adult, and after further moults, the adult form is finally reached. Some crustaceans continue to moult as adults, while for others, the development of 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...
s signals the final moult.
Any organs which are absent from the adults do not generally appear in the larvae, although there are a few exceptions, such as the vestige of the fourth pereiopod in the larvae of Lucifer
Lucifer (prawn)
Lucifer is a little-known and degenerate genus of prawns, the only genus in the family Luciferidae. Lucifer has a long body, but many fewer appendages than other prawns, with only three pairs of pereiopods remaining, all without claws. It also bears no gills. The females, uniquely among prawns,...
, and some pleopods in certain Anomura
Anomura
Anomura is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans includes the word crab, all true crabs are in the sister group to the Anomura, the Brachyura .-Description:The name Anomala reflects the unusual variety of forms in this group;...
and 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.
History of the study of crustacean larva
Antonie van Leeuwenhoek was the first person to observe the difference between larval crustaceans and the adults when he watched the eggs of CyclopsCyclops (genus)
Cyclops is one of the most common genera of freshwater copepods, comprising over 400 species . The name Cyclops comes from the Cyclops of Greek mythology which shares the quality of having a single large eye, which may be either red or black in Cyclops.Cyclops individuals may range from...
hatching in 1699. Despite this, and other observations over the following decades, there was controversy among scientists about whether or not metamorphosis
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
occurred in crustaceans, with conflicting observations presented, based on different species, some of which went through a metamorphosis, and some of which did not. This controversy persisted until the 1840s, and the first descriptions of a complete series of larval forms were not published until the 1870s (Sidney Irving Smith
Sidney Irving Smith
Sidney Irving Smith was an American zoologist.-Private life:Sidney Smith was the son of Elliot Smith and Lavinia Barton. His brother in law was Addison Emery Verrill. Smith married Eugenia Pocahontas Barber in New Haven, Connecticut on June 29, 1882...
on the American lobster
American lobster
The American lobster, Homarus americanus, is a species of lobster found on the Atlantic coast of North America, chiefly from Labrador to New Jersey. Within North America, it is also known as the northern lobster or Maine lobster. It can reach a body length of , and a mass of over , making it the...
in 1873; Georg Ossian Sars on the European lobster
European lobster
Homarus gammarus, known as the European lobster or common lobster, is a species of clawed lobster from the eastern Atlantic Ocean, Mediterranean Sea and parts of the Black Sea. It is closely related to the American lobster, H. americanus. It may grow to a length of and a mass of , and bears a...
in 1875, and Walter Faxon
Walter Faxon
Walter Faxon was an American ornithologist and carcinologist. He was born on 1848-02-04 at Jamaica Plain, Massachusetts, where he grew up. His brother Charles Faxon was a botanist. He received three degrees from Harvard University. One of his greater ornithological achievements was the...
on the shrimp Palaemonetes vulgaris
Palaemonetes vulgaris
Palaemonetes vulgaris, variously known as the common American prawn, common grass shrimp, marsh grass shrimp or marsh shrimp, is a common species of shrimp in the western Atlantic Ocean from Cape Cod Bay to the Gulf of Mexico. Adults grow to less than long, and are transparent except for some...
in 1879).
Larval stages
Nauplius
The genus name Nauplius was published posthumously by Otto Friedrich MüllerOtto Friedrich Müller
Otto Friedrich Müller, also Mueller was a Danish naturalist.-Biography:Müller was born in Copenhagen. He was educated for the church, became tutor to a young nobleman, and after several years' travel with him settled in Copenhagen in 1767, and married a lady of wealth.His first important works,...
in 1785 for animals now known to be the larvae of copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s. The nauplius stage (plural: nauplii) is characterised by the use of the appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...
s of the head (the antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
) for swimming. The nauplius is also the stage at which a simple, unpaired eye first appears. The eye is known for that reason as the "naupliar eye", and is often absent in later developmental stages, although it is retained into the adult form in some groups, such as the Notostraca
Notostraca
The order Notostraca comprises the single family Triopsidae, containing the tadpole shrimp or shield shrimp. The two genera, Triops and Lepidurus, are considered living fossils, having not changed significantly in outward form since the Triassic. They have a broad, flat carapace, which conceals the...
.
Zoea
The genus Zoea was initially described by Louis Augustin Guillaume BoscLouis Augustin Guillaume Bosc
Louis Augustin Guillaume Bosc was a French botanist, invertebrate zoologist, and entomologist.-Biography:...
in 1802 for an animal now known to be the larva of a 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...
. The zoea stage (plural: zoeas or zoeae) is characterised by the use of the thoracic
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
appendages for swimming.
Post-larva
The post-larva is characterised by the use of abdominal appendages (pleopods) for propulsion. The post-larva is usually similar to the adult form, and so many names have been erected for the stage in different groups. William Elford LeachWilliam Elford Leach
William Elford Leach FRS was an English zoologist and marine biologist.Leach was born at Hoe Gate, Plymouth, the son of a solicitor. At the age of twelve he went to school in Exeter, studying anatomy and chemistry. By this time he was already collecting marine samples from Plymouth Sound and along...
erected the genus Megalopa in 1813 for a post-larval crab; a 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...
post-larva is called a parva; hermit crab
Hermit crab
Hermit crabs are decapod crustaceans of the superfamily Paguroidea. Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell that is carried around by the hermit crab.-Description:...
post-larva are called glaucothoe.
Branchiopoda
In the Branchiopoda, the most basal group of crustaceans, there is no metamorphosis; instead, the animal grows through a series of moults, with each moult adding segments to the body, but without any dramatic changes in form. Every other crustacean group with free larvae shows a metamorphosisMetamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
, and this difference in the larvae is thought to reflect "a fundamental cleavage" of the crustaceans.
Cephalocarida
In the MediterraneanMediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
horseshoe shrimp
Cephalocarida
Cephalocarida is a class inside the subphylum Crustacea that comprises only twelve shrimp-like benthic species. They were discovered in 1955 by Howard L. Sanders, and are commonly referred to as horseshoe shrimps. They have been grouped together with the Remipedia in the Xenocarida...
Lightiella magdalenina, the young experience 15 metanaupliar stages and 2 juvenile stages, with each of the first six stages adding 2 trunk segments, and the last four segments being added singly.
Remipedia
The larvae of remipedesRemipedia
Remipedia is a class of blind crustaceans found in coastal aquifers which contain saline groundwater, with populations identified in almost every ocean basin so far explored, including in Australia, the Caribbean Sea, the Atlantic Ocean...
are lecithotrophic, consuming egg yolk
Egg yolk
An egg yolk is a part of an egg which feeds the developing embryo. The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalazae...
rather than using external food sources. This characteristic, which is shared with malacostracan groups such as the Decapoda and Euphausiacea (krill) has been used to suggest a link between Remipedia and Malacostraca.
Malacostraca
Amphipod hatchlings resemble the adults.Young isopod
Isopoda
Isopods are an order of peracarid crustaceans, including familiar animals such as woodlice and pill bugs. The name Isopoda derives from the Greek roots and...
crustaceans hatch directly into a manca stage, which is similar in appearance to the adult. The lack of a free-swimming larval form has led to high rates of endemism in isopods, but has also allowed them to colonise the land, in the form of the woodlice
Woodlouse
A woodlouse is a crustacean with a rigid, segmented, long exoskeleton and fourteen jointed limbs...
.
Stomatopoda
The larvae of many groups of mantis shrimpMantis shrimp
Mantis shrimp or stomatopods are marine crustaceans, the members of the order Stomatopoda. They are neither shrimp nor mantids, but receive their name purely from the physical resemblance to both the terrestrial praying mantis and the shrimp. They may reach in length, although exceptional cases of...
are poorly known. In the superfamily Lysiosquilloidea, the larvae hatch as antizoea larvae, with five pairs of thoracic appendages, and develop into erichthus larvae, where the pleopods appear. In the Squilloidea, a pseudozoea larva develops into an alima larva, while in Gonodactyloidea, a pseudozoea develops into an erichthus.
A single fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
stomatopod larva has been discovered, in the Upper Jurassic Solnhofen
Solnhofen limestone
The Solnhofen Plattenkalk is a Jurassic Konservat-Lagerstätte that preserves a rare assemblage of fossilized organisms, including highly detailed imprints of soft bodied organisms such as sea jellies...
lithographic limestone
Lithographic Limestone
Lithographic limestone is hard limestone that is sufficiently fine-grained, homogeneous and defect free to be used for lithography. Geologists use the term lithographic texture to refer to a grain size under 1/250 mm...
.
Krill
The life cycle of krill is relatively well understood, although there are minor variations in detail from species to species. After hatching, the larvae go through several stages called nauplius, pseudometanauplius, metanauplius, calyptopsis and furcilia stages, each of which is sub-divided into several sub-stages. The pseudometanauplius stage is exclusive to the so-called "sac-spawners". Until the metanauplius stage, the larvae are reliant on the yolk reserves, but from the calyptopsis stage, they begin to feed on phytoplanktonPhytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
. During the furcilia stages, segments with pairs of swimmerets are added, beginning at the frontmost segments, with each new pair only becoming functional at the next moult. After the final furcilia stage, the krill resembles the adult.
Decapoda
Apart from the prawnPrawn
Prawns are decapod crustaceans of the sub-order Dendrobranchiata. There are 540 extant species, in seven families, and a fossil record extending back to the Devonian...
s of the suborder Dendrobranchiata, all decapod crustaceans brood their eggs on the female's pleopods. This has resulted in development in decapod crustaceans being generally abbreviated. There are at most 9 larval stages in decapods, as in krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
, and both decapod nauplii and krill nauplii often lack mouthparts and survive on nutrients supplied in the egg yolk
Egg yolk
An egg yolk is a part of an egg which feeds the developing embryo. The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalazae...
(lecithotrophy). In species with normal development, eggs are roughly 1% of the size of the adult; in species with abbreviated development, and therefore more yolk in the eggs, the eggs may reach 1/9 of the adult's size.
The post-larva of 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...
is called parva, after the species Acanthephyra parva described by Henri Coutière, but which was later recognised as the larva of Acanthephyra purpurea.
In the marine 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...
s, there are three larval stages, all similar in appearance.
Freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
crayfish
Crayfish
Crayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...
embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s differ from those of other crustaceans in having 40 ectoteloblast cells, rather than around 19. The larvae show abbreviated development, and hatch with a full complement of adult appendages with the exceptions of the uropods and the first pair of pleopods.
The larvae of the Achelata
Achelata
The Achelata is an infra-order of the reptant Decapoda. It contains the spiny lobsters , the slipper lobsters and the furry lobsters...
(slipper lobster
Slipper lobster
Slipper lobsters are a family of decapod crustaceans found in all warm oceans and seas. Despite their name, they are not true lobsters, but are more closely related to spiny lobsters and furry lobsters. Slipper lobsters are instantly recognisable by their enlarged antennae, which project forward...
s and spiny lobster
Spiny lobster
Spiny lobsters, also known as langouste or rock lobsters, are a family of about 45 species of achelate crustaceans, in the Decapoda Reptantia...
s) are unlike any other crustacean larvae. The larvae are known as phyllosoma, after the genus Phyllosoma erected by William Elford Leach
William Elford Leach
William Elford Leach FRS was an English zoologist and marine biologist.Leach was born at Hoe Gate, Plymouth, the son of a solicitor. At the age of twelve he went to school in Exeter, studying anatomy and chemistry. By this time he was already collecting marine samples from Plymouth Sound and along...
in 1817. They are flattened and transparent, with long legs and eyes on long eyestalks. After passing through 8–10 phyllosoma stages, the larva undergoes "the most profound transformation at a single moult in the Decapoda", when it develops into the so-called puerulus stage, which is an immature form resembling the adult animal.
The members of the traditional infraorder Thalassinidea
Thalassinidea
Thalassinidea is an infraorder of decapod crustaceans that live in burrows in muddy bottoms of the world's oceans. In Australian English, the littoral thalassinidean Trypaea australiensis is referred to as the yabby , frequently used as bait for estuarine fishing; elsewhere, however, they are...
can be divided into two groups on the basis of their larvae. According to Robert Gurney
Robert Gurney
Robert Gurney was a British zoologist most famous for his monographs on British Freshwater Copepoda and the Larvae of Decapod Crustacea . He was not affiliated with any institution, but worked at home, initially in Norfolk, and later near Oxford...
, the "homarine group" comprises the families Axiidae
Axiidae
Two separate animal families have been recognized with the name Axiidae:*AxiidaeHuxley, 1879, Decapoda, based on the genus Axius, crustaceans*Cimeliidae, the family containing the European gold moths...
and Callianassidae
Callianassidae
Callianassidae is a family of ghost shrimp of the order Decapoda. It is divided into 13 subfamilies and 42 genera:Anacallianacinae*Anacalliax de Saint Laurent, 1973Bathycalliacinae*Bathycalliax Sakai & Türkay, 1999Callianassinae...
, while the "anomuran group" comprises the families Laomediidae and Upogebiidae
Upogebiidae
Upogebiidae is a family of mud shrimp in the order Decapoda.-Genera:*Acutigebia Sakai, 1982*Aethogebia A. B. Williams, 1993*Arabigebicula Sakai, 2006*Austinogebia Ngoc-Ho, 2001*Gebiacantha Ngoc-Ho, 1989*Gebicula Alcock, 1901...
. This split corresponds with the division later confirmed with molecular phylogenetics.
Among the Anomura
Anomura
Anomura is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans includes the word crab, all true crabs are in the sister group to the Anomura, the Brachyura .-Description:The name Anomala reflects the unusual variety of forms in this group;...
, there is considerable variation in the number of larval stages. In the South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
n freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
genus Aegla, the young hatch from the eggs in the adult form. Squat lobster
Squat lobster
Squat lobsters are decapod crustaceans of the families Galatheidae, Chirostylidae and Kiwaidae, including the common genera Galathea and Munida. They are not lobsters at all, but are more closely related to porcelain crabs, hermit crabs and then, more distantly, true crabs...
s pass through four, or occasionally five, larval states, which have a long rostrum
Rostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
, and a spine on either side of the carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
; the first post-larva closely resembles the adult. Porcelain crab
Porcelain crab
Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs. They are typically less than wide, and have flattened bodies as an adaptation for living in rock crevices...
s have two or three larval stages, in which the rostrum and the posterior spine on the carapace are "enormously long". Hermit crab
Hermit crab
Hermit crabs are decapod crustaceans of the superfamily Paguroidea. Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell that is carried around by the hermit crab.-Description:...
s pass through around four larval stages. The post-larva is known as the glaucothoe, after a genus named by Henri Milne-Edwards
Henri Milne-Edwards
Henri Milne-Edwards was an eminent French zoologist.Henri Milne-Edwards was the 27th child of William Edwards, an English planter and militia colonel in Jamaica and Elisabeth Vaux, a French. He was born in Bruges, Belgium, where his parents had retired. At that time, Bruges was a part of the...
in 1830. The glaucothoe is 3 millimetre (0.118110236220472 in) long in Pagurus longicarpus
Pagurus longicarpus
Pagurus longicarpus, the long-clawed hermit crab, is a small common subtidal decapod ranging out to deep found living in shells from periwinkles, oyster drills, and eastern mud snails. It is found from Nova Scotia to Florida and Texas....
, but glaucothoe larvae up to 20 mm (0.78740157480315 in) are known, and were once thought to represent animals which had failed to develop correctly. Like the preceding stages, the glaucothoe is symmetrical, and although the glaucothoe begins as a free-swimming form, it often acquires a gastropod shell
Gastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
to live in; the coconut crab
Coconut crab
The coconut crab, Birgus latro, is a species of terrestrial hermit crab, also known as the robber crab or palm thief. It is the largest land-living arthropod in the world, and is probably at the upper size limit of terrestrial animals with exoskeletons in today's atmosphere at a weight of up to...
, Birgus latro, always carries a shell when the immature animal comes ashore, but this is discarded later.
Although they are classified as 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, the larvae of Dromiacea
Dromiacea
Dromiacea is a group of crabs, ranked as a section. It contains 240 extant and nearly 300 extinct species. Where they are considered to form a monophyletic group, Dromiacea and two other groups of crabs, namely the Raninoida and Cyclodorippoidea, may be collected together into the Podotremata, each...
are similar to those of the Anomura, which led many scientists to place dromiacean crabs in the Anomura, rather than with the other crabs. Apart from the Dromiacea, all crabs share a similar and distinctive larval form. The crab zoea has a slender, curved abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
and a forked telson
Telson
The telson is the last division of the body of a crustacean. It is not considered a true segment because it does not arise in the embryo from teloblast areas as do real segments. It never carries any appendages, but a forked "tail" called the caudal furca is often present. Together with the...
, but its most striking features are the long rostral and dorsal spines, sometimes augmented by further, lateral spines. These spines can be many times longer than the body of the larva. Crab prezoea larvae have been found fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
ised in the 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...
contents of the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
bony fish
Osteichthyes
Osteichthyes , also called bony fish, are a taxonomic group of fish that have bony, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species...
Tharrhias
Tharrhias
Tharrhias is an extinct genus of prehistoric bony fish that lived during the Aptian stage of the Early Cretaceous epoch.-See also:* Prehistoric fish* List of prehistoric bony fish...
.
Copepoda
CopepodCopepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s have six naupliar stages, followed by a stage called the copepodid, which has the same number of body segments and appendages in all copepods. The copepodid larva has two pairs of unsegmented swimming appendages, and an unsegmented "hind-body" comprising the thorax and the abdomen. There are typically five copepodid stages, but parasitic copepods may stop after a single copepodid stage. Once the gonads develop, there are no further moults.
Facetotecta
The single genus in the FacetotectaFacetotecta
Facetotecta is a poorly known infraclass of thecostracan crustaceans. The adult forms have never been recognised, and the group is known only from its larvae, the "y-nauplius" and "y-cyprid" larvae...
, Hansenocaris, is only known from its larvae. They were first described by Christian Andreas Victor Hensen
Victor Hensen
Christian Andreas Victor Hensen was a German zoologist . He coined the term plankton and laid the foundation for biological oceanography....
in 1887, and named "y-nauplia" by Hans Jacob Hansen
Hans Jacob Hansen
-References:*.-Literature:...
, assuming them to be the larvae of barnacle
Barnacle
A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...
s. The adults are presumed to be parasites
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
of other animals.