Pterosoma planum

There are some odd creatures in the world. Take this fascinating animal for instance:

Pterosoma planum pelagic snail (License image)

It is a snail, similar to the curly-shelled ones you've undoubtedly seen on land, except this one swims around in the ocean. Yes, swims rather than crawl.

It is carnivorous. It hunts other gastropods as well as small fish and probably other things as well.

In the photo above, the pink tube sticking up is the animal's mouth. At the base of the mouth are two eyes/ visual organs. I do not know how good the snail's visual resolution is. Also sticking up, sort of to the mid-rear and looking a bit like a transluscent keel is the snail's swimming fin. It flaps and waves with a S-curve pattern for locomotion. Sticking out beneath the snail is a vestigial shell that holds and protects vital organs.

I assume the pretty pinkish-white polka dots are for decoration. Snail's gotta have style after all.

The animal was around 4cm long (1.5inches ±). Though it might look like I took the photo at night, it was actually 10:30am on a bright sunny day, in shallow water. A lot of pelagic animals had been swept into a bay by strong winds and heavy seas the previous night.

Here is a head-on view, with the mouth/ proboscis and eyes oriented downward, vestigial shell in the background and up:

Pterosoma planum pelagic snail front view (License image)