Caribbean Umbraculum - mating

April 7, 2003
From: Dee Scarr

Several years ago, in March, I discovered my first Umbraculum, under the Pier here on Bonaire, in the Netherlands Antilles, just north of Venezuela. I kept track of the critter until one day I found only its shell. I never saw another one - or thought to look for one, actually - until last month, when I found one on a night dive. Two days later I dived to find it, and found only the shell.

This time, though, it struck me that there might be more. Two days ago I found two individuals, about 15' apart: both were partly buried in sand, one up next to a rock and the other in the middle of a sand patch. This afternoon [4 April 2003] when I returned to try to photo them, I found the one in the sand patch easily, and began taking photos. Suddenly I noticed the second individual, just below the first but almost completely buried in the sand, front to front with the first. If this isn't a mating, it's just before or just after one, I think. The attached photos aren't the quality I'd hoped for, but I may have had better luck with film; I'll know tomorrow.

The eggs would be likely to be deposited under a rock ledge? A ribbon spiral about the same diameter as the parent? Do you think it's likely that their appearance is related to mating, or is it just coincidence I've only seen them during this time of year?

Thanks for any info you can give me on this fascinating creature.
Dee Scarr

Scarr, D., 2003 (Apr 7) Caribbean Umbraculum - mating. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Dee,
Thanks for these interesting observations. I have put a pointer to what I guess is the gap between the shell and the body of the buried slug in both your photos. I don't think I have seen photos of Umbraculum mating so that's a first. As you will see in my earlier discussion of Ross Willis' photo of Umbraculum, this animal has its penis and female genital opening right at the front of the body below the head tentacles and above the mouth so I guess they can only mate by standing head to head. If you see them doing this again it would be of great interest to find out how they actually mate. We know very little about the biology of Umbraculum and there is some debate about whether the the structure I have identified in Ross Willis's photo is the actual penis or whether it is an external accessory flap. Pruvot-Fol (1960) has suggested that she thinks there is a penial papillae which is only visible when it is everted during copulation. It's probably not the easiest thing to do [or see] but if you do see a couple mating again perhaps you could gently pull them apart and see if the 'penis' is inserted in its partner or whether there is a thin white tube inserted instead.

Concerning the egg ribbon. There is a photo in Peggy Cable's message. It looks a bit 'limp' because it as out of water at low tide, but it gives you an idea of what the ribbon should look like. I don't know if their appearance is related to mating. Umbraculum lives for at least a year and I assume that it stays quite close to its food sponge most of the time. I guess it's possible they may go 'looking' for a partner away from their sponge when they reach sexual maturity, but as far as I know, their biology and natural history has never been studied in any detail.

Look at the other messages on this page and also have a look at the Umbraculum umbraculum. Although I have put your message on the Umbraculum mediterraneum page, as you will see in earlier discussions, it is probable that there is only one species of Umbraculum, and it has a worldwide distribution.
Best wishes
Bill Rudman

Rudman, W.B., 2003 (Apr 7). Comment on Caribbean Umbraculum - mating by Dee Scarr . [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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