Thecacera sp.

Photo courtesy of Webmaster
Tulamben, Bali, Indonesia
Sept. 2002

Thecacera sp.

The animal being featured this week is not new to the Slug Site having been profiled as previously as BOW #177 and BOW #249 . There have also been a number of submissions to Bill Rudman's Sea Slug Forum where Bill has assigned it as Thecacera sp. 2 pending the development of more information on the animal. Years ago it was observed that Thecacera picta seemed to have the ability to contract by means of expelling body fluids (possibly water) which made it very difficult to locate the animal after depositing it in a bucket overnight for safe keeping. This observation was filed in the folder of unexplained mysteries of nature and forgotten until our recent trip to Tulamben, Bali, Indonesia this September.

During this trip my dive buddy Alan Grant (aka the diving dentist) and myself were able to locate a couple of individuals who pretty much stayed in the same area. The pair seemed to demonstrate the ability to extend the branchial appendages immediately behind the gills as the occasion suited (as seen in photo to the left). Almost to the extent observed in the manner of the very bizarre Thecacera sp. featured on the back book cover of Debelius's Indo -Pacific Field Guide for Nudibranchs and Sea Snails . What's going on here?? Is this extension hydraulically activated? Is it a sensory system of some kind??

All of the above is conjecture on my part and has no scientific basis. I am however inviting comment for those who may be able to shed some light on our observations.

Alan was able to obtain quite remarkable video of the animal which he kindly agreed to share with the readers of this site. The video is being presented in both Windows Media (1.3 megs) and Quick Time (0.6 megs) for your enjoyment!

Send Alan mail at

Michael Miller
San Diego, CA
Nov., 2002

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