Mystery slug from Malaysia

March 26, 2003
From: Michael Smith

In the past eight months, I have seen many large slugs (measured from 20 to 30 cm) in waters off the west coast of penisular Malaysia. The slug is only seen at night and often a half dozen can be found during a single dive. No experienced diver recalls seeing these locally more than a year ago. They all appear as a solid dark red color and have the two "knobs" above the head but no other apparent marking (to my novice eye). Sorry that I can't give any more information until my next night dive; I am new at trying to identify things I see in the sea. If no one knows what these may be, maybe you can tell me what to look for next time. Just keep in mind that I can't tell a gill from a gall bladder so please talk to me like you would to your 12 year old child!
Michael Smith

Dear Michael,
Firstly is there any chance of a photo? As you say you're a novice, the biggest hurdle when trying to describe something in words is knowing what is important. Making a slightly educated guess from what you've told me - large and common, dark red, 2 knobs above the head. There are a few possibilities.

One is Pleurobranchus forskalii. If you look at that page in the Forum and the attached messages below you will see it ranges in colour from a light mottled brown to a dark red. Prod one and see if it has a large gill on the right side of the body below the mantle skin flap. Another possibility is Pleurobranchus grandis which has a similar colour range. Pleurobranchs always have a large gill on the right side of the body

Failing that you might have a Sea Hare. There is a lot on the Forum about these animals - which can be large and numerous. Go to the sea hare page for links to lots of information. One clue is that most species squirt out a purple ink if they are disturbed or prodded.

Let me know if any of these guesses are winners - but best of all see if you can send a photo
Best wishes,

Rudman, W.B., 2003 (Mar 26). Comment on Mystery slug from Malaysia by Michael Smith. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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