Melibe megaceras - detail of the head

April 17, 2003
From: Bill Rudman

Here are three enlargements from Harry Erhardt's photos of Melibe megaceras to show the detail of the head and associated structures.

Mantanani Is, near Kota Kinabalu, Sabah, Malaysia. In 24m depth [19-24 March, 2003] Photos: Harry Erhardt

Upper Right: In this dorsal shot of the head, the shadowy outline of the sensory tentacles around the lip of the oral hood can be seen through the transparent skin. These tentacles are constantly moving 'feeling' over the surface of the sand as the animal crawls along, trying to locate the small crustacea it feeds on. The brown specks which can be seen all over the skin are clusters of the symbiotic zooxanthellae I describe on the Fact Sheet. On the dorsal surface of the oral hood are a series of long tapering papillae which are attached some distane in from the edge. I have no idea whether they have a special sensory purpose. I rather suspect that, like the ones all over the back, they are just another place to 'farm' zooxanthellae. Also on the oral hood are a pair of rhinophores, the nudibranch chemosensory organ. In this photo we can only see the left rhinophore. It is the structure that runs from the oral hood up to the top of the photo. The slightly curved, and thicker, bottom half of this structure is the rhinophore stalk, or more correctly the rhinophore sheath. At the top of the sheath sits the very small, pointed, rhinophore club, and behind it is a long thin tapering flagellum.

Lower Photos: These photos show the same structures from different angles. In particular, the left photo shows the dorsal tentacles on the oral hood standing upright, and they show the rhinophore stalk/sheath and the posterior flagellum a little more clearly. The flagellae have small pointed papillae scattered over them. Both these photo show animals with some whitish patching on the body.

Best wishes,
Bill Rudman

Rudman, W.B., 2003 (Apr 17) Melibe megaceras - detail of the head. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Melibe megaceras

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