The alpheid that lives inside sponges and on crinoids, with eyes visible from above.
A stout snapping shrimp, most animals well under 3 cm, with one claw enlarged and the other small, the same asymmetry that marks the family. The separation from Alpheus is the eyes: in this genus they are exposed and can be seen from above, where in Alpheus the carapace is produced forward over them and hides them. Colour runs translucent, orange, red-brown and cream, often with banding on the abdomen, and the body is usually shorter and more compact than the burrowing alpheids on open sand.
The habitat is another animal. Species in this genus live in the internal canals of sponges, among the arms of feather stars and in the crevices of coral rubble, and they are found by examining a host rather than by searching ground. A single large sponge may hold dozens, and on a crinoid this shrimp shares the host with Laomenes, the squat lobster Allogalathea elegans and a clingfish. The snap is used as it is in the rest of the family, against rivals and prey, and much of the crackle coming from a sponge-covered rubble patch is these animals rather than the ones in burrows.
The genus is the one in which eusociality was first described in the sea. Colonies of a single breeding female with many non-breeding animals, defended by large-clawed individuals, were worked out in Caribbean sponge-dwelling species, and social organisation of some degree occurs elsewhere in the genus. Species are separated on the rostrum, the claw and the appendages, so records from a dive stay at the genus. Recorded from about 3 to 30 m.
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.