Actinocyclus verrucosus from eastern Australia [3]

August 10, 2005
From: Bill Rudman

I have been trying to find a good photo of living Actinocyclus verrucosus without success but did find some field drawings I did of a specimen from northern New South Wales of an animal on its food sponge. Although not immediately obvious from photos taken of animals off their food, they are remarkbaly well camouflaged on their food sponges. In this case the sponge has similar brown specks to the animal, and the blackish spots on the tips of the papillae mimic the oscules or pores in the sponge colony. I have not had the sponge indentified, but it has the smooth leathery feel of a species of Halisarca

Locality:  sth side Split Solitary Is., northern new South Wales, eastern Australia. 12 m. 18 Sept 1988. ['one eating sponge almost identical in colour. The black spots represent the oscules on the sponge colony' ]. 31mm long alive live length 3 cm. AM C157079. Drawings by Bill Rudman.

The lower drawing shows the head in action. One external anatomical feature of Actinocyclus is the way the head and anterior foot are fused so that when they are feeding, there is a small chamber formed over the sponge as the radula rasps bits of tissue off the colony. In the lower drawing the raised bit with the two little tentacles is the open mouth through which the buccalb bulb and radular ribbon are protruded, and you can see the side of the foot is joined to the mouth to form a hood. Dendrodoris has a similar arrangement, but I have always assumed that was independently developed for suctorial feeding, as a means of containing the digestive secretions exuded in those animals to partially digest the sponge more sucking it in.

Best wishes
Bill Rudman

Rudman, W.B., 2005 (Aug 10) Actinocyclus verrucosus from eastern Australia [3]. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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