Glassy, bilaterally symmetrical larvae of sea stars, urchins and sea cucumbers, with nothing of the adult about them.
Transparent larvae built on bands of cilia, and among the least animal-looking things a blackwater dive produces. Sea stars pass through a bipinnaria and then a brachiolaria, a clear lobed shape with paired arms and a ciliated band running round the whole outline. Sea cucumbers produce an auricularia, a folded transparent sheet with a looping band along its edges. Urchins and brittle stars produce plutei, a set of long straight arms held apart at sharp angles and stiffened internally by calcareous rods, which is why a pluteus in a beam looks like a piece of glass drawing rather than an animal.
None of this resembles the adult, and that is the point of the group: the radial body of the settled animal is built inside the larva as a separate structure, and at settlement most of the larval body is discarded. The gut, the ciliated bands and in the plutei the rods are usually all that a photograph resolves.
The larvae are common in the water column at night and are met at every blackwater site in the region. Identification below phylum is not reasonable from a photograph, and even the broad type is easier to state than the class: a plutei with four arms and a plutei with eight belong to different groups, but a damaged or foreshortened one settles nothing.
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.
