Hallaxa michaeli on food sponge

Dear Nick,

Thanks for this great series of photos. It illustrates the close relationships these three species have to each other - Hallaxa michaeli feeding only on the sponge Halisarca laxus, and the sponge being found only on the stalked ascidian Pyura. For those of you not familar with Pyura, it is a stalked solitary ascidian, often found in groups or quite large beds. In Nick's photo the whole ascidian, stalk and body, are covered in a layer of sponge.

In your photo we can see the Hallaxa can burrow quite deeply into the sponge tissue, and its almost transparent mantle renders it almost invisible on its prey. In an earlier message [#17219] you mention finding Hallaxa on different coloured sponges. From you photo here it seems that the one colony of the sponge can range in colour through cream, brown, yellow and pink - which is new information on the sponge Halisarca laxus.

Best wishes,
Bill Rudman