''Pleurobranchus areolatus'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of pleurobranchid

sea slug Sea slug is a common name for some Marine biology, marine invertebrates with varying levels of resemblance to terrestrial Slug, slugs. Most creatures known as sea slugs are gastropods, i.e. they are Sea snail, sea snails (marine gastropod moll ...

, a type of marine

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

, commonly found in the

Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

. It is up to 15 cm long and it feeds on ascidians.

Taxonomy

Although there were believed to occur six species of ''Pleurobranchus'' in the Caribbean Sea, the other five (''P. atlanticus'' Abbott, 1949, ''P. evelinae'' Thompson, 1977, ''P. crossei'' Vayssière, 1896, ''Susania gardineri'' White, 1952, ''P. reesi'' White, 1952 and ''P. emys'' Ev. Marcus, 1984) were synonymized with ''P. areolatus'' in 2015, based on molecular and morphological evidence.Goodheart J., Camacho-García Y., Padula V., Schrödl M., Cervera J. L., Gosliner T. M. & Valdés Á. (2015). "Systematics and biogeography of ''Pleurobranchus'' Cuvier, 1804, sea slugs (Heterobranchia: Nudipleura: Pleurobranchidae)". ''

Zoological Journal of the Linnean Society The ''Zoological Journal of the Linnean Society'' is a monthly peer-reviewed scientific journal covering zoology published by Oxford University Press on behalf of the Linnean Society. The editor-in-chief is Maarten Christenhusz (Linnean Society) ...

'' 174(2): 322–362. . The specific names ''P. areolatus'' and ''P. evelinae'' were also commonly in use in literature, while other names were not. There is no known

type material In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

of ''Pleurobranchus areolatus'', ''Susania gardineri'' and ''P. reesi'', but the anatomy of Mörch's type specimen was illustrated by

Rudolph Bergh Rudolph Bergh (15 October 1824 – 20 July 1909), full name Ludvig Sophus Rudolph Bergh, was a Danish physician and malacologist. He worked in Copenhagen. As a doctor his speciality was sexually transmitted diseases. In Copenhagen a hospital a ...

in 1897. Type material of ''P. atlanticus'' is stored at the National Museum of Natural History (Smithsonian Institution), the

Academy of Natural Sciences of Drexel University The Academy of Natural Sciences of Drexel University, formerly the Academy of Natural Sciences of Philadelphia, is the oldest natural science research institution and museum in the Americas. It was founded in 1812, by many of the leading natur ...

and the

Museum of Comparative Zoology The Museum of Comparative Zoology (formally the Agassiz Museum of Comparative Zoology and often abbreviated to MCZ) is a zoology museum located on the grounds of Harvard University in Cambridge, Massachusetts. It is one of three natural-history r ...

. Those of ''P. crossei'' and ''P. evelinae'' are at the

National Museum of Natural History (France) The French National Museum of Natural History ( ; abbr. MNHN) is the national natural history museum of France and a of higher education part of Sorbonne University. The main museum, with four galleries, is located in Paris, France, within the J ...

and the

Natural History Museum, London The Natural History Museum in London is a museum that exhibits a vast range of specimens from various segments of natural history. It is one of three major museums on Exhibition Road in South Kensington, the others being the Science Museum (Lo ...

, respectively. The

sister species In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

(the closest relative) is ''

Pleurobranchus varians ''Pleurobranchus varians'' is a species of sea slug, a sidegill slug, a marine gastropod mollusc in the family Pleurobranchidae. Taxonomy The sister species (the closest relative) is '' Pleurobranchus areolatus'' from Caribbean.Goodheart J., ...

'' from the Central Pacific. Those two species split 3.10 million years ago (the

Isthmus of Panama The Isthmus of Panama, historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North America, North and South America. The country of Panama is located on the i ...

formed 3.1–3.4 Mya). Both species have color morphs and for their proper determination the knowledge of their locality is needed.

Distribution

''Pleurobranchus areolatus'' occurs off Mexico, Costa Rica, Venezuela, Brazil, Jamaica, Puerto Rico, St. Thomas, Aruba, St. Maarten/St Martin, Bahamas, Bermuda, Panama, Canary Islands and Madeira. This was the only species of ''Pleurobranchus'' considered to occur in the

until 2016, when '' Pleurobranchus iouspi'' was reported from

Santa Marta Santa Marta (), officially the Distrito Turístico, Cultural e Histórico de Santa Marta (), is a port List of cities in Colombia, city on the coast of the Caribbean Sea in northern Colombia. It is the capital of Magdalena Department and the fou ...

, Colombia. The type locality is

Saint Thomas, U.S. Virgin Islands Saint Thomas (, , ) is one of the Virgin Islands in the Caribbean Sea, and a constituent district of the United States Virgin Islands (USVI), an unincorporated territory of the United States. Along with surrounding minor islands, it is one of t ...

. ''P. areolatus'' was also reported from the eastern Pacific, but those records were identified as '' Pleurobranchus digueti'' in 2015.

Description

The shape of the body is oval. The dorsum contains numerous small, polygonal and flat tubercles. The background color ranges from light brown to deep violet, with varying degrees of opaque white pigment on the tubercles. In some cases the opaque white pigment is arranged in a symmetrical pattern across the body. It is up to 150 mm long.

Rhinophores A rhinophore is one of a pair of chemosensory club-shaped, rod-shaped or ear-like structures which are the most prominent part of the external head anatomy in sea slugs, marine gastropod opisthobranch mollusks such as the nudibranchs, sea hare ...

are rolled and fused at the base, with horizontal striations from base to tip. The color pattern of rhinophores is the same as color pattern of the body.Alvim J. & Pimenta A. D. (2016). "Comparative Morphology and Redescription of ''Pleurobranchus'' Species (Gastropoda, Pleurobranchoidea) from Brazil". ''

Zoological Studies ''Zoological Studies'' is a peer-reviewed open access scientific journal covering zoology, with focuses on animal behavior, comparative physiology, evolution, ecology, systematics and biogeography. It is published by the Biodiversity Research Cente ...

'' 55(15): . A well marked pedal gland is visible at the posterior end of the foot in some preserved specimens. The

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses Science Biology * Seashell, a hard outer layer of a marine ani ...

is reduced and internal (as in all other ''Pleurobranchus'' species). The shell itself does not allow proper species identification within the genus ''Pleurobranchus''. The shape of the shell is oval. The

protoconch A protoconch (meaning first or earliest or original shell) is an embryonic or larval shell which occurs in some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod. In older texts it is also called " ...

has one

whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). In nature File:Photograph and axial plane floral diagra ...

and the size of the protoconch is about 400 μm. The most recent drawing of the reproductive system was published by Goodheart et al. (2015) and by Alvim & Pimenta (2016). The genital cup is just before the gill on the right side of the body. The

reproductive system The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are al ...

is triaulic (it has two female openings and one male opening). The shape of the prostate is elongated and the frontal part of the prostate is rounded. The

radula The radula (; : radulae or radulas) is an anatomical structure used by mollusks for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters ...

has 73 rows, it has no central tooth and it has 115 lateral teeth on both sides (radular formula 73 × 115.0.115), while the radular formula reported from smaller specimens (27 mm) is 66 × 90.0.90. The gill has the size of 2/3 of the body in living specimens of 27 mm in length. The

circulatory system In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart ...

was described by Alvim & Pimenta in detail in 2016, but it is the same as in ''

Pleurobranchus reticulatus ''Pleurobranchus'' is a genus of sea slugs, specifically side-gill slugs, marine gastropod mollusc in the family Pleurobranchidae. They typically occur in intertidal and shallow subtidal waters of tropical and subtropical seas worldwide. Spe ...

''. They also described the

nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...

, which is very similar to that of ''P. reticulatus''.

Ecology

''Pleurobranchus areolatus'' was found to be abundant in

Biscayne Bay Biscayne Bay is a lagoon with characteristics of an estuary located on the Atlantic coast of South Florida. The northern end of the lagoon is surrounded by the densely developed heart of the Miami metropolitan area while the southern end is large ...

, Florida in 1946. Minimum recorded depth is 0 m. Maximum recorded depth is 70 m.Welch J. J. (2010). "The “Island Rule” and Deep-Sea Gastropods: Re-Examining the Evidence". '' PLoS ONE'' 5(1): e8776. doi:10.1371/journal.pone.0008776. This species is found under rocks and coral rubble. For example in Florida it is sometimes found among ''

Porites porites ''Porites porites'', commonly known as hump coral or finger coral, is a species of stony coral in the genus ''Porites''. It is found in the Caribbean Sea and western Atlantic Ocean and also along the coast of West Africa. Description ''Porites p ...

'' corals. They are laying large, translucent and gelatinous egg masses during spring in Florida. All species in the genus ''Pleurobranchus'' are carnivorous. ''P. areolatus'' probably feeds on

ascidians Ascidiacea, commonly known as the ascidians or sea squirts, is a paraphyletic class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer test or "tunic" made of the polysaccharid ...

, for example, ''

Didemnum ''Didemnum'' is a genus of colonial tunicates in the family Didemnidae. It is the most speciose genus in the didemnid family. Species in this genus often have small calcareous spicules embedded in the tunic and form irregular or lobed colonies. S ...

'' sp. Its

ectoparasites Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...

include copepod '' Anthessius ovalipes''.Walter T. Chad (2015). ''Anthessius ovalipes'' Stock, Humes & Gooding, 1963. In: Walter, T.C. & Boxshall, G. (2015). World of Copepods database. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=348850 on 2016-10-15 Rodriguesic acids and its esters (they are modified

diketopiperazine A diketopiperazine (DKP), also known as a ''dioxopiperazine'' or ''piperazinedione'', is a class of organic compounds related to piperazine but containing two amide linkages. DKP's are the smallest known class of cyclic peptide. Despite their name ...

s) were isolated from ''P. areolatus'' in 2014.Pereira F. R., Santos M. F., Williams D. E., Andersen R. J., Padula V., Ferreira A. G. & Berlinck R. G. (2014). "Rodriguesic acids, modified diketopiperazines from the gastropod mollusc ''Pleurobranchus areolatus''". ''

Journal of the Brazilian Chemical Society The Journal of the Brazilian Chemical Society (print , eISSN , CODEN JOCSET) is a Brazilian scientific journal in chemistry. It was founded in 1990 and is published by the '' Brazilian Society of Chemistry'' (''Sociedade Brasileira de Química''), ...

'' 25(4): 788–794. . These are the first diketopiperazine derivatives isolated from a mollusc. Similar diketopiperazines were isolated also from ascidians ''

'' sp. These derivatives may either result from a ''P. areolatus''

symbiont Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biological interaction, between two organisms of different species. The two organisms, termed symbionts, can fo ...

or may come from feeding on the ascidian. These chemical compounds may be used by ''P. areolatus'' as a

chemical defense Chemical defense is a strategy employed by many organisms to avoid consumption by producing toxic or repellent metabolites or chemical warnings which incite defensive behavioral changes. The production of defensive chemicals occurs in plants, fung ...

Gallery

Pleurobranchus areolatus map.png, Distribution of ''P. areolatus'' Pleurobranchus areolatus shell.png, Drawing of dorsal view of the internal shell. Pleurobranchus areolatus shell 2.png, Drawing of ventral view of the internal shell including the hyaline sheath. Pleurobranchus areolatus reproductive system.png,

Reproductive system The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are al ...

of ''Pleurobranchus areolatus'' by

R. Tucker Abbott Robert Tucker Abbott (September 28, 1919 – November 3, 1995) was an American conchology, conchologist and malacology, malacologist. He was the author of more than 30 books on malacology, which have been translated into many languages. Abbot ...

(1949). Pleurobranchus crossei.jpg, Left side view. Pleurobranchus areolatus (Warty Sidegill Slug).jpg, Left side view. Pleurobranchus areolatus 2.png, Drawing of right side view showing the position of the internal shell, the gill, anus behind the gill, and genital pore in front of the gill. Pleurobranchus areolatus 3.png, Drawing ventral view shows rhinophores, anterior sinus, velum, foot, gill and posterior pedal gland.

References

This article incorporates Creative Commons (CC-BY-4.0) text from the referenceGoodheart J. A., Ellingson R. A., Vital X. G., Galvão Filho H. C., McCarthy J. B., Medrano S. M., Bhave V. J., García-Méndez K., Jiménez L. M., López G. & Hoover C. A. (2016). "Identification guide to the heterobranch sea slugs (Mollusca: Gastropoda) from Bocas del Toro, Panama". ''Marine Biodiversity Records'' 9(1), p.56. and public domain text from the reference {{taxonbar, from=Q5048433 Pleurobranchidae Gastropods described in 1863