Melibe megaceras Sea Slug from the Water Tables

Melibe megaceras in HIMB water table.   Photo Kyle Landers

Dan Jennings-Kam from the Gates Lab asked me the other day who was keeping the Melibe nudibranchs in the research tables behind the NSF building.  

After looking at him blankly for a moment, I said,"what Melibe's?" (having never actually even seen one in Hawai'i). But upon investigating, there they were, roaming the abandoned bottom sections of several tanks, resembling very much the swimming anemones with which they were sharing the tank, and the bottom muck covering the tank. 

Once seen though, they were obvious and impressive. 

They are camouflaged, big (for Hawaii), bizarre looking, they swim, they spread out like a sea weed or sea anemone and - two weeks later - they have all disappeared. Most likely they have laid their eggs and finished their life cycle (check out the Sea Slug Forum of Hawai'i site for Dan's close up of the eggs as well. See: http://seaslugsofhawaii.com/species/Melibe-megaceras-a.html)

So a bit about these animals. The Melibe group are unusual in that rather than having a regular head - they have an inflated oral hood that they use to feed on tiny bottom dwelling crustaceans. Take a look at the image below.

Photo Kyle Landers

Next, they have cerata (the feathery/furry shaped structures found on many sea slugs), but in this case, besides ones that look like anemone tentacles going up, they have large  forked cerata out to the sides, making them look most un-sea slug like (and why at a glance, I did not even notice them).

Add in a swimming ability (not that unusual, think of the Spanish Dancer nudibranch that undulates so nicely), but this fold up lengthwise and then flips side to side.

And finally, they have the same symbiotic algae as corals, but according to one researcher (Kempf, 1984) they may not be as great of host, possibly digesting some of the crop for food. Rudman noted that this makes them sort of an intermediate host on the way to being fully solar powered.
According to Gosliner, they are found on sand flats. A look through the various images I could find online from around the world shows the species mostly on sand or silt bottoms, although some were in algae or sea grasses as well.
Let's hope another crop recruits to our water tanks and thanks to Dan for spotting these. I will add more pictures next week.

References:
(accessed 8/3/2012)

• Gosliner, T.M. (1987) Review of the nudibranch genus Melibe (Opisthobranchia: Dendronotacea) with descriptions of two new species. The Veliger, 29(4): 400-414.
http://researcharchive.calacademy.org/research/scipubs/pdfs/v54/proccas_v54_n18.pdf
• Kempf, S. C. 1984. Symbiosis between the zooxanthella Symbiodinium (=Gymnodinium) microadriaticum (Freudenthal) and four species of nudibranchs. Biological Bulletin, 166(1): 110-126.
http://www.biolbull.org/content/166/1/110.short

Check out the articles on Melibe megaceras on the Sea Slug Forums and Keoki and Yuko's site!

• The Sea Slug Forum:
http://www.seaslugforum.net/melimega.htm
• Sea Slug Forum of Hawai'i
http://seaslugsofhawaii.com/species/Melibe-megaceras-a.html
• Solar Throw-net Slug: 
http://www.marinelifephotography.com/marine/mollusks/slugs/melibe-megaceras.htm