Roboastra luteolineata eating Nembrotha kubaryana

February 7, 2006
From: K. Anderson


Found this tenacious Roboastra luteolineata beginning to devour a larger Nembrotha kubaryana yesterday. I watched for quite a while and returned to the action repeatedly through the dive - no matter what the N. kubaryana did, the R. luteolineata hung on. At one stage the predator was hanging off the prey by its mouth only before gaining a grip and piggybacking.

You can see the definitive oral tentacles that help ID this as R. luteolineata (instead of Tambja affinis ). You can also see that both species have bits sticking out their sides; I thought these were their sexual organs. Is there some reaction that takes place to cause this and if so, can you explain?

Locality: Lighthouse Bay, Ningaloo Reef, Western Australia, Indian Ocean. Depth: 12 m. Length: R. luteolineata 3 cm; N. kubaryana 6 cm ish. 04 February 2006. limestone/hard coral reef; sandy surrounds. Photographer: Kristin Anderson

Kristin Anderson

kristin@OceansByAnderson.com

Anderson, K.J., 2006 (Feb 7) Roboastra luteolineata eating Nembrotha kubaryana. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/15757

Dear Kristin,
The feeding behaviour is enough to separate the Roboastra from a bryozoan feeding Tambja. This is a nice observation as it is only the third record we have of this species feeding - all three observations being recorded on the Forum. Nembrotha morosa, Tamba verconis, and now N. kubaryana.

Concerning the reproductive organs protruding. I suspect this is to do with the nature of the body rather than any misplaced hormones. These animals have no hard skeleton so their shape is totally dependent on muscles working against their hydroskeleton. They are in fact a bag of watery blood. If you think of a rubber glove with its fingers popped inside out. If you fill the glove with water one or more of the fingers is going to pop out when the pressure increases enough. You can see that the Roboastra has pushes all its fluid to the front half of the body, presumably to help push out the buccal bulb so it can engulf the Nembrotha. I suspect the partial eversion of the reproductive organs is result of the greatly increased pressure in that part of the body. I am not sure why Nembrotha has also partially everted these organs, but I guess quite a lot of cross-wires are occurring in its little brain as it fights for its life.
Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Feb 7). Comment on Roboastra luteolineata eating Nembrotha kubaryana by K. Anderson. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/15757

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