A transparent swimming polychaete with rows of paddles and, in some species, yellow light.
A wholly transparent, gelatinous worm that swims in open water. The body is flattened, with a row of paired parapodia down each side ending in flat paddles, and two long tentacular cirri that sweep back from the head alongside the body. Unlike almost every other polychaete it carries no bristles apart from a pair of long rods on the first segment, which is part of why it looks more like a piece of clear jelly than like a worm. Most are 1 to 5 cm. The confusions are the arrow worms, which have their own entry and are stiff, finned and without parapodia, and the alciopid worms, which are also transparent swimmers but carry a pair of very large lensed eyes that Tomopteris does not. Species are separated on parapodial and chaetal detail and the genus is the honest record.
It is an active predator and swims continuously, driving a wave along the paddles from back to front. Copepods, arrow worms, larvae and other polychaetes are all taken. Bioluminescence has been reported in several species, produced by glands in the parapodia and yellow rather than the blue-green that almost everything else in the ocean emits; it is not something that shows while a focus light is on the animal, and it is not the reason one is usually found.
They occur through the water column and are met at the depths a blackwater dive works. Nothing about the animal is robust: a worm held in a beam for a long time, or caught in the wash of a fin, is easily damaged.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
