Biologists Identify New Sea Slug Species

Newswise — The lettuce sea slug, Elysia crispata, a species living in the Florida Keys, the Caribbean and South America, is well known to aquarists and biologists, having been identified and named in 1863. However, recent comparisons between E. crispata, collected from the Florida Keys, with sea slugs collected from St. Thomas in the Virgin Islands, reveal differences (both in morphology and DNA) significant enough for USF biologists to name a new species of sea slug - Elysia clarki - named for the late Kerry B. Clark, biologist and professor at the Florida Institute of Technology.

Sea slugs are relatively small, colorful, shell-less denizens of mainly tropical waters. They creep or sometimes swim in shallow waters and eat small animals and plant life.

"The differences between E. crispata and E. clarki exist at every level," said Skip Pierce, chair of the Department of Biology at the University of South Florida. "There are morphological, developmental, feeding and molecular differences, and very important habitat differences."

The newly named species may be unique to the Florida Keys, living in mooring canals and borrow pits, in very shallow water.

According to Pierce, lead author of the paper published in Molluscan Research (26:1) announcing the new species, the existence of E. clarki was unknown by the 19th century biologists who named E. crispata, although they - and biologists to come later - may well have collected and worked on E. clarki, not realizing it was a separate species.

"The two species are closely related but genetically distinct," explained Pierce.

The two species do bear observable similarities. For example, both are green because of symbiotic chloroplasts from the algae they eat. (See: "USF biologist investigate gene-thieving sea slugs" http://usfnews.usf.edu/page.cfm?link=article&aid=216)

"Chloroplasts are the structures in plant cells that conduct photosynthesis," explained Pierce. "Sea slug cells capture chloroplasts from the algae they eat, take them up and keep them working. When slugs are in the sunlight, they photosynthesize to get energy, just as plants do."

Both species have white spots and are often blazed with a band of orange. However, their parapodia (frilly structures located on the slug's back), are slightly different. Too, they live in very different habitats, the food preferences of the juveniles are different, their microscopic anatomy differs and the two species have different digestive system anatomy. Once more, and most conclusively, their genes have different DNA sequences.

The differences between the two slugs are such that the Florida Keys animals represent a new species, concluded Pierce and colleagues.

However, the new species may already be at-risk.

"Some of our collecting sites have already been filled in for condo development," noted Pierce. "The older species lives out on the reefs, but the new species lives right on the islands. Since E. clarki may be unique to the Florida Keys, some conservation concerns could be appropriate."