Cittarium pica
Encyclopedia
Cittarium pica, common name
the West Indian top shell or magpie shell, is a species
of large edible sea snail
, a marine
gastropod mollusk in the family
Turbinidae
. This species has a large black and white shell
.
This snail is known as "wilks" (or sometimes as "whelks") in the English-speaking Caribbean islands of the West Indies, where this is a popular food item. The word "wilks" is used as a singular form as well as a plural. This species is however not at all closely related to the species that are known as whelk
s in the U.S. and in Europe. In some Spanish-speaking parts of the Caribbean, when used as a food source Cittarium pica is known as bulgao, or simply as caracoles (snails, in spanish). In Venezuela it is called quigua.
Cittarium pica is considered the third most economically
important invertebrate species in the Caribbean
, after the spiny lobster
(Panulirus argus
) and the queen conch (Eustrombus gigas), and is being extirpated due to overfishing
and overexploitation
.
. The vetigastropods are considered to be among the most primitive living gastropods, and are widely distributed in all oceans of the world. It is also part of the superfamily Trochoidea
, presenting nacre
as the inner shell layer, and its subordinated family Turbinidae
. Woodring et al. (1924) recombined this species as Cittarium picum. Weisbord (1962) recombined it as Livona pica, and it was finally recombined as Cittarium pica by Philippi (1847), Rosenberg (2005) and Hendy et al. (2008).
This is the only living species in the genus Cittarium. There was known only one species in the genus Cittarium for a long time, However in 2002, a fossil species Cittarium maestratii
Lozouet, 2002 from the Oligocene
deposits of southwestern France
was discovered and named.
of this species can be up to 137 mm in maximum dimension. It is very thick and heavy, having an outline that is between trochiform
and turbiniform
in shape, with rounded shoulders and a somewhat low conical form. The shell of Cittarium pica presents a rather wide umbilicus, which is deep and devoid of sculpture. The aperture is distinguishably nacreous
, as is the case in other Trochoidea
, and is circular. The parietal callus
is glossy and delicate, and has a node that projects towards the umbilicus. Juvenile
individuals possess shells ornamented by spiral lines and strong cords, in contrast to the nearly smooth, homogeneous surface of mature
specimens.
The color pattern is rather distinct, overall white with black zigzag spots on each whorl
. Those spots have a tendency to become axial lines in older, larger individuals. The aperture is commonly white, with an inner iridescence because of the nacre.
Unusual erosion
On some old, empty shells of large individuals, the black colored parts become slightly higher in relief, compared to the white areas surrounding it. This unusual morphology may be due to the action of blue-green algae, such as Plectonema terebrans, which continuously erode the surface of the white parts of the shell.
, and in the Caribbean coast of Mexico
, Costa Rica
, Panama
, Colombia
and Venezuela
. It also occurs in the Bahamas, Cuba
, the Cayman Islands
, Jamaica
, Haiti
and the Dominican Republic
, and the Lesser Antilles
as far south as Trinidad and Tobago
. The species has been reintroduced to Bermuda
.
, which means each individual organism belonging to this species is distinctly male or female. The fertilisation
in this species occurs externally
. During the reproductive season, which normally occurs from June to November in the field, male individuals release their sperm into the water, as females simultaneously release their green colored unfertilised egg
s. The encounter of those gamete
s produce yolky fertilised eggs, which will further develop into lecitotrophic (yolk feeding) larvae
. They emerge from the egg capsules as shell-cap-bearing trocophores. These trocophore larvae do not spend much time in the plankton, because settlement occurs relatively soon, after 3.5 to 4.5 days.
Individuals usually reach sexual maturity
at shell lengths of 32-34 mm. The life span of this species is still unknown, but estimates for other top shells reach 30 years.
, feeding on a large variety of algae
, and sometimes also on detritus
. They actively scrape the algal growths off rocks, and this tends to cause erosion
over time. Feeding commonly occurs during the nocturnal period, when the snails are most active.
, Lottia leucopleura
, often lives on the underside of the shell of this large sea snail. The crab Pinnotheres barbatus is mentioned as a commensal. The sessile vermetid
gastropod Dendropoma corrodens
(also known as ringed wormsnail) and the tube dwelling polychaete
Spirorbis
may live attached to the shell of Cittarium pica, as is also the case for several species of algae.
The shell of this species is very popular indeed as "housing" for the large land hermit crab species Coenobita clypeatus.
. This caused a serious impact on the Land hermit-crab populations, because these arthropods need empty Cittarium pica shells (or some other similar shell) to use as shelter. Nowadays, Cittarium pica is a legally protected species in Bermuda, where its collection is forbidden.
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
the West Indian top shell or magpie shell, is a 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 large edible sea snail
Sea snail
Sea snail is a common name for those snails that normally live in saltwater, marine gastropod molluscs....
, a marine
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...
gastropod mollusk in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Turbinidae
Turbinidae
Turbinidae, the turban snails, are a family of small to large marine gastropods. Turbinidae have a strong, thick calcareous operculum readily distinguishing them from the somewhat similar Trochidae or top snails, which have a corneous operculum...
. This species has a large black and white 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...
.
This snail is known as "wilks" (or sometimes as "whelks") in the English-speaking Caribbean islands of the West Indies, where this is a popular food item. The word "wilks" is used as a singular form as well as a plural. This species is however not at all closely related to the species that are known as whelk
Whelk
Whelk, also spelled welk or even "wilks", is a common name used to mean one or more kinds of sea snail. The species, genera and families referred to using this common name vary a great deal from one geographic area to another...
s in the U.S. and in Europe. In some Spanish-speaking parts of the Caribbean, when used as a food source Cittarium pica is known as bulgao, or simply as caracoles (snails, in spanish). In Venezuela it is called quigua.
Cittarium pica is considered the third most economically
Economy
An economy consists of the economic system of a country or other area; the labor, capital and land resources; and the manufacturing, trade, distribution, and consumption of goods and services of that area...
important invertebrate species in the Caribbean
Caribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
, after the spiny lobster
Panulirus argus
Panulirus argus, the Caribbean spiny lobster, is a species of spiny lobster that lives on reefs and in mangrove swamps in the western Atlantic Ocean.-Anatomy:...
(Panulirus argus
Panulirus argus
Panulirus argus, the Caribbean spiny lobster, is a species of spiny lobster that lives on reefs and in mangrove swamps in the western Atlantic Ocean.-Anatomy:...
) and the queen conch (Eustrombus gigas), and is being extirpated due to overfishing
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
and overexploitation
Overexploitation
Overexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Sustained overexploitation can lead to the destruction of the resource...
.
Taxonomy
Cittarium pica is within the clade VetigastropodaVetigastropoda
Vetigastropoda is a major taxonomic group of sea snails, marine gastropod mollusks that form a very ancient lineage. Taxonomically Vetigastropoda are sometimes treated as an order although they are a clade in Bouchet and Rocroi, 2005....
. The vetigastropods are considered to be among the most primitive living gastropods, and are widely distributed in all oceans of the world. It is also part of the superfamily Trochoidea
Trochoidea (superfamily)
Trochoidea is a superfamily of small to very large vetigastropod sea snails with gills and an operculum.They have nacre as the inner shell layer...
, presenting nacre
Nacre
Nacre , also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer; it is also what makes up pearls. It is very strong, resilient, and iridescent....
as the inner shell layer, and its subordinated family Turbinidae
Turbinidae
Turbinidae, the turban snails, are a family of small to large marine gastropods. Turbinidae have a strong, thick calcareous operculum readily distinguishing them from the somewhat similar Trochidae or top snails, which have a corneous operculum...
. Woodring et al. (1924) recombined this species as Cittarium picum. Weisbord (1962) recombined it as Livona pica, and it was finally recombined as Cittarium pica by Philippi (1847), Rosenberg (2005) and Hendy et al. (2008).
This is the only living species in the genus Cittarium. There was known only one species in the genus Cittarium for a long time, However in 2002, a fossil species Cittarium maestratii
Cittarium maestratii
Cittarium pica is an extinct species of a sea snail, a marine gastropod mollusk in the family Turbinidae.It is known from Chattian, that is stage of a Late Oligocene.-External links:*...
Lozouet, 2002 from the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
deposits of southwestern France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
was discovered and named.
Shell description
The shellGastropod 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...
of this species can be up to 137 mm in maximum dimension. It is very thick and heavy, having an outline that is between trochiform
Trochidae
The Trochidae, common name top snails, are a taxonomic family of very small to large sea snails, marine gastropod molluscs in the clade Vetigastropoda ....
and turbiniform
Turbinidae
Turbinidae, the turban snails, are a family of small to large marine gastropods. Turbinidae have a strong, thick calcareous operculum readily distinguishing them from the somewhat similar Trochidae or top snails, which have a corneous operculum...
in shape, with rounded shoulders and a somewhat low conical form. The shell of Cittarium pica presents a rather wide umbilicus, which is deep and devoid of sculpture. The aperture is distinguishably nacreous
Nacre
Nacre , also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer; it is also what makes up pearls. It is very strong, resilient, and iridescent....
, as is the case in other Trochoidea
Trochoidea (superfamily)
Trochoidea is a superfamily of small to very large vetigastropod sea snails with gills and an operculum.They have nacre as the inner shell layer...
, and is circular. The parietal callus
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...
is glossy and delicate, and has a node that projects towards the umbilicus. Juvenile
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
individuals possess shells ornamented by spiral lines and strong cords, in contrast to the nearly smooth, homogeneous surface of mature
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
specimens.
The color pattern is rather distinct, overall white with black zigzag spots on each whorl
Whorl (mollusc)
A whorl is a single, complete 360° revolution or turn in the spiral growth of a mollusc shell. A spiral configuration of the shell is found in of numerous gastropods, but it is also found in shelled cephalopods including Nautilus, Spirula and the large extinct subclass of cephalopods known as the...
. Those spots have a tendency to become axial lines in older, larger individuals. The aperture is commonly white, with an inner iridescence because of the nacre.
Unusual erosion
On some old, empty shells of large individuals, the black colored parts become slightly higher in relief, compared to the white areas surrounding it. This unusual morphology may be due to the action of blue-green algae, such as Plectonema terebrans, which continuously erode the surface of the white parts of the shell.
Distribution
This species occurs rarely in the Florida KeysFlorida Keys
The Florida Keys are a coral archipelago in southeast United States. They begin at the southeastern tip of the Florida peninsula, about south of Miami, and extend in a gentle arc south-southwest and then westward to Key West, the westernmost of the inhabited islands, and on to the uninhabited Dry...
, and in the Caribbean coast of Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
, Costa Rica
Costa Rica
Costa Rica , officially the Republic of Costa Rica is a multilingual, multiethnic and multicultural country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west and the Caribbean Sea to the east....
, Panama
Panama
Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...
, Colombia
Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...
and Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...
. It also occurs in the Bahamas, Cuba
Cuba
The Republic of Cuba is an island nation in the Caribbean. The nation of Cuba consists of the main island of Cuba, the Isla de la Juventud, and several archipelagos. Havana is the largest city in Cuba and the country's capital. Santiago de Cuba is the second largest city...
, the Cayman Islands
Cayman Islands
The Cayman Islands is a British Overseas Territory and overseas territory of the European Union located in the western Caribbean Sea. The territory comprises the three islands of Grand Cayman, Cayman Brac, and Little Cayman, located south of Cuba and northwest of Jamaica...
, Jamaica
Jamaica
Jamaica is an island nation of the Greater Antilles, in length, up to in width and 10,990 square kilometres in area. It is situated in the Caribbean Sea, about south of Cuba, and west of Hispaniola, the island harbouring the nation-states Haiti and the Dominican Republic...
, Haiti
Haiti
Haiti , officially the Republic of Haiti , is a Caribbean country. It occupies the western, smaller portion of the island of Hispaniola, in the Greater Antillean archipelago, which it shares with the Dominican Republic. Ayiti was the indigenous Taíno or Amerindian name for the island...
and the Dominican Republic
Dominican Republic
The Dominican Republic is a nation on the island of La Hispaniola, part of the Greater Antilles archipelago in the Caribbean region. The western third of the island is occupied by the nation of Haiti, making Hispaniola one of two Caribbean islands that are shared by two countries...
, and the Lesser Antilles
Lesser Antilles
The Lesser Antilles are a long, partly volcanic island arc in the Western Hemisphere. Most of its islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean, with the remainder located in the southern Caribbean just north of South America...
as far south as Trinidad and Tobago
Trinidad and Tobago
Trinidad and Tobago officially the Republic of Trinidad and Tobago is an archipelagic state in the southern Caribbean, lying just off the coast of northeastern Venezuela and south of Grenada in the Lesser Antilles...
. The species has been reintroduced to Bermuda
Bermuda
Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...
.
Ecology
Habitat
This large snail is found on or under rocks, in exposed and moderately sheltered shores, both in intertidal and shallow subtidal zones. Cittarium pica generally does not live at great depths, though this has occasionally been reported. Most individuals are found at the water's edge, and have little tendency to disperse. Minimum recorded depth is 0 m. Maximum recorded depth is 7 m.Life cycle
Cittarium pica is dioeciousDioecious
Dioecy is the property of a group of biological organisms that have males and females, but not members that have organs of both sexes at the same time. I.e., those whose individual members can usually produce only one type of gamete; each individual organism is thus distinctly female or male...
, which means each individual organism belonging to this species is distinctly male or female. The fertilisation
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...
in this species occurs externally
External fertilization
External fertilization is a form of fertilization in which a sperm cell is united with an egg cell external to the bodies of the reproducing individuals. In contrast, internal fertilization takes place inside the female after insemination through copulation....
. During the reproductive season, which normally occurs from June to November in the field, male individuals release their sperm into the water, as females simultaneously release their green colored unfertilised egg
Egg (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...
s. The encounter of those gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s produce yolky fertilised eggs, which will further develop into lecitotrophic (yolk feeding) larvae
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
. They emerge from the egg capsules as shell-cap-bearing trocophores. These trocophore larvae do not spend much time in the plankton, because settlement occurs relatively soon, after 3.5 to 4.5 days.
Individuals usually reach sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at shell lengths of 32-34 mm. The life span of this species is still unknown, but estimates for other top shells reach 30 years.
Feeding habits
The west Indian top shell is known to be an herbivoreHerbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
, feeding on a large variety of algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
, and sometimes also on detritus
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
. They actively scrape the algal growths off rocks, and this tends to cause erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
over time. Feeding commonly occurs during the nocturnal period, when the snails are most active.
Biological interactions
A small limpetLimpet
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...
, Lottia leucopleura
Lottia leucopleura
Lottia leucopleura is a species of sea snail, a true limpet, a marine gastropod mollusk in the family Lottiidae, one of the families of true limpets....
, often lives on the underside of the shell of this large sea snail. The crab Pinnotheres barbatus is mentioned as a commensal. The sessile vermetid
Vermetidae
Vermetidae, common name the worm snails or worm shells, is a taxonomic family of small to medium-sized sea snails, marine gastropod molluscs in the clade Littorinimorpha....
gastropod Dendropoma corrodens
Dendropoma corrodens
Dendropoma corrodens is a species of small sea snail, a marine gastropod mollusk in the family Vermetidae, the worm snails or worm shells....
(also known as ringed wormsnail) and the tube dwelling polychaete
Polychaete
The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
Spirorbis
Spirorbis
Spirorbis is a genus of very small polychaete worms, usually with a white coiled shell. Members of the genus live in the lower littoral and sublittoral zones of rocky shores. Spirorbis worms usually live attached to seaweeds, but some species live directly on rocks, shells or other hard substrates...
may live attached to the shell of Cittarium pica, as is also the case for several species of algae.
The shell of this species is very popular indeed as "housing" for the large land hermit crab species Coenobita clypeatus.
Human use
These large sea snails are boiled and eaten in a variety of different local recipes. Because of their popularity as a food item and the problem of overfishing, in the US Virgin Islands there are territorial regulations to protect these snails: no collecting is allowed during their reproductive season, and there is a minimum harvest size regulation. For a similar reason, Cittarium pica became locally extinct in BermudaBermuda
Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...
. This caused a serious impact on the Land hermit-crab populations, because these arthropods need empty Cittarium pica shells (or some other similar shell) to use as shelter. Nowadays, Cittarium pica is a legally protected species in Bermuda, where its collection is forbidden.
Further reading
- Díaz-Ferguson E., Haney R., Wares J. & Silliman B. (2010). "Population Genetics of a Trochid Gastropod Broadens Picture of Caribbean Sea Connectivity". PLoS ONEPLoS ONEPLoS ONE is an open access peer-reviewed scientific journal published by the Public Library of Science since 2006. It covers primary research from any discipline within science and medicine. All submissions go through an internal and external pre-publication peer review but are not excluded on the...
5(9): e12675. doi:10.1371/journal.pone.0012675.