Okenia rhinorma

Photo was taken at Dive Site Mato Point, Anilao, Batangas, Philippines
Found by Dive Guide Alexis Principe
Photo courtesy of Kevin Lee
Copyright 2011

Okenia rhinorma Rudman, 2007

This is one of the strangest looking slugs you will ever find. Hard to even imagine it belongs to the genus Okenia, but that's where Bill Rudman (Sea Slug Forum) put it.

The name says it all. This species has huge rhinophores situated far back on the dorsum, immediately in front of the gill. Rudman's trivial name for the species breaks down to mean - rhino (for rhinophores) overlapping with inorma (enormous). Perfect.

Another unique character belonging to this species is the "snow plow" like ridge surrounding the rhinophores and gill. When Kevin's dive guide Alexis Principe found this specimen it was plowing along just under the surface of the bottom. Only the rhinophores and gill were exposed. Kind of like a submarine cruising just under the surface with only the conning tower exposed above water. Again, how perfect?

Since the specimen kept diving out of sight into the sediment, Kevin had to get creative. To take this photo, Kevin took a piece of old, waterlogged bamboo and photographed the slug, crawling on it.

The body is variously white with grey mottling and large orange spots. It reaches about 10mm in length. So far the geographic range includes the Indian Ocean of Tanzania and the Red Sea to Australia, Indonesia, the Philippines, Japan and Hawai'i.

We don't really know anything about the biology of this species, but with its subterranean, plowing behavior, it must be feeding on infaunal organisms. Rudman suggests it is an ascidian-feeding species because of similarities in body shape and the morphology of the radula of a species from the North Atlantic which has been identified as Okenia aspersa . This may now be confirmed based on John Chuk's observation (Sea Slug Forum).

Good show Kevin!

Dave Behrens
Gig Harbor, Washington
May., 2011

Kevin Lee, Dave Behrens, and Christiane Waldrich relaxing after a hard day of slug hunting at Villa Markisa in June, 2010!

Send Dave mail at davidwbehrens@gmail.com
Send Kevin mail at diverkevin@gmail.com
Send Christiane mail at christiane@villa-markisa.com

© The Slug Site, Michael D. Miller 2011. All Rights Reserved.