Well hello there, Umbraculum umbraculum, what a very cute face you have! Cute, but strange – the whole mass there is the creature ... as Dave Behrens writes on slugsite:
Umbraculum is truly one of the oddest opisthobranchs I have seen. To begin with it is one of the Pleurobranchs, or side gilled sea slugs. While all other pleurobranchs, except Tylodina have retained a thin internal shell, these two more primitive genera have an external shell. Because the animal has no means to keep the shell clean of growth of other encrusting animals, specimens often carry quite a collection of animals, such as sponges and anemones and sometimes even algae and other assorted grunge on the shell surface.
Photographer John Turnbull notes of the image above, "The colour differential (more red on the left side) is because my white video light was on that side – so it received more red light. The right side of the animal just had natural light from above, in which the red is attenuated by the water."
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