Learchis poica

Learchis poica  Ev. Marcus & Er. Marcus, 1960

Learchis poica @ Lake Worth Lagoon, Florida, USA by Sandra Edwards

Description
Small nudibranch up to 14mm in length. Quite variable in color, the typical pattern is the translucent body with white patching on the head and behind the rhinophores that may form a broad continuous median dorsal band from the front of the head to the tip of the tail. There can also be an opaque white irregular band along each side of the body, below the cerata. It has orange markings on the head, often consisting of an orange line from the base of the oral tentacles to the base of the rhinophores. There can also be an orange patch on each side of the head (cheek patch) that could be replaced by an orange line from the base of the rhinophores to the foot, or from below the rhinophores forward to the front of the head below the oral tentacles. The rhinophores are often described as annulate, perfoliate or lamellate, but they consistently have an irregular arrangement of 6-10 rings or annulations, some of which are irregular or incomplete (Edmunds, 1964). The oral tentacles are smooth. The cerata stand in about 8 groups laid in arches, the hindmost of which are indistinctly separated; they are translucent with a few scattered white patches (covering most of the cerata in certain specimens), a subterminal white band (there could be an orange band in certain specimens) and a white cnidosac on the tip. The digestive gland can be seen, by transparency, inside the cerata and it could be colored from light brown to dark brown or even black. The eyes are black. The foot is narrower than the body, specially in the anterior side, it has a bilabiate anterior border with tappered propodial tentacles normally facing backwards as the animal moves. The tail is short.

Biology
The animals appear to move little. Sometimes it forms clusters on the hydroids they feed on (Halocordyle disticha in the Canary Islands). It has the ability to retain undischarged nematocysts from their preys and store them in the cnidosacs at the tips of cerata. The spawn is a convoluted spiral of white eggs laid on the hydroids they feed on.

Etymology

• Learchis, of uncertain meaning, seems related to the Greek mythology, where there’s a story about Ino (a mortal queen of Thebes) and Athamas (a Boeotian king, son of Aeolus and Enarete) who hunted his own son Learchos as a stag and slew him. Classical authors like Bergh rarely explained the origins of the names they proposed, but they used to inspire in the Greek and Roman mythology.
• Poica. No information available about the origin of the specific name.

Distribution
The present species is the first Atlantic member of the genus, and it has been found in Aruba, Bahamas, Barbados, Cayman Islands, Costa Rica, Curaçao, Grenada, Jamaica, Martinique, Mexico, Puerto Rico, St. Lucia, St. Vincent & the Grenadines, Virgin Islands, USA and Venezuela. Also in Ghana, West Africa (Edmunds, 1968), Madeira (Cervera & Malaquias, unpubl. data), Azores (Moro, pers.comm.) and the Canary Islands (Moro, Bacallado y Ortea, 2010).

More pictures

Bibliography

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Bibliography based on the works by Steve Long, 2006. Bibliography of Opisthobranchia 1554-2000 and Gary McDonald, 2009. Bibliographia Nudibranchia, with later updates from other resources.

Further reading

• Biodiversity Heritage Library
• Flickr pictures
• Interim Register of Marine and Nonmarine Genera
• Jacksonville Shells
• NCBI GenBank
• Nudibranchs defend themselves with their food
• OBIS - Search by Taxon
• Sea Slug Forum
• Sea Slugs Guadeloupe
• World Register of Marine Species

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Acknowledgments
Many thanks to Sandra Edwards, Judy Townsend, Lureen Ferretti and specially to Anne DuPont by putting us in contact with her diving buddies who provided us the Florida pictures of Learchis poica illustrating the record of this species. Thank you very much as well to Susan and Rick Coleman by the Bonaire pictures of Learchis poica, that show a chromatic variation not present in Florida.