17 new brilliantly colored species of sea slugs described

From lavender to orange, pink to yellow polka dots — researchers have just described 17 stunning new species of sea slugs that live among coral reefs in the Indo-Pacific region.

All the species belong to the genus Hypselodoris, a group of colorful sea slugs that make for striking photo models. In a recent study, researchers from the California Academy of Sciences (CAS) reorganized the genus Hypselodoris, adding new-to-science species to the group and revealing secrets of the evolution of their brilliant color patterns.

Discovery of the new species is a great feeling, said Terrence Gosliner, senior curator at the Department of Invertebrate Zoology at the CAS. “Several species [of Hypselodoris] had not been studied previously from a genetic perspective and we had reason to believe that we had discovered a bunch of new species, based on their external appearance,” he told Mongabay.

Among the new species are Hypselodoris confetti, a sea slug that looks like it’s covered in shreds of brightly colored paper; H. rositoi, named for its distinctive rose-pink shade; and H. skyleri, a sea slug with white spots that resemble stars in the sky and that’s named after co-author Rebecca Johnson’s son, Skyler (Sky) Rodgers.

The reorganization of species within Hypselodoris using genetic tools also helped the researchers gain an insight into why the sea slugs are so colorful. “This is the first time we’ve had a family tree to test longstanding hypotheses for how patterns evolve,” Gosliner said.

The CAS team found, for instance, that a number of distant relatives have independently evolved the same color pattern — like H. iba and H. bullocki, both lavender in color. The two species are, however, not closely related. “The more likely explanation for their similar appearance is that they reside in the same geographic region where being purple is advantageous for avoiding predators either as camouflage or warning of distastefulness,” Johnson, citizen science lead at the CAS, said in a statement.

Surprisingly, H. iba itself has two different forms of individuals: one lavender with a white stripe, and the other cream with a lavender stripe and orange spots. The two forms have been photographed mating and are nearly genetically identical.

“We are not sure of why this is the case but suspect that predators cannot recognize the difference between the two color morphs,” Gosliner said. Such differently colored individuals have not been seen in other Hypselodoris species.

So far, none of the newly described species seem to be at any immediate risk of extinction.

“But with climate change impacts, this could change fairly quickly if coral reefs continue to disappear,” Gosliner said. Moreover, many more species of sea slugs are yet to be discovered.

“Even with these discoveries, still less than 10 percent of the species inhabiting the planet have been recognized. There is still much fundamental work to do,” Gosliner added.

Citation:

Epstein, H. E., Hallas, J. M., Johnson, R. F., Lopez, A., & Gosliner, T. M. (2018). Reading between the lines: Revealing cryptic species diversity and colour patterns in Hypselodoris nudibranchs (Mollusca: Heterobranchia: Chromodorididae). Zoological Journal of the Linnean Society.