ShrimpfishesCentriscidae

The spike at the back end of a shrimpfish is not its tail. It is the first spine of the dorsal fin, carried right at the rear of the body where the tail ought to be, and the real tail has been pushed down and forward underneath it, along with the soft dorsal and the anal fin, into a small cluster of fins on the underside of the hind corner. Everything other fish keep at the end, this one keeps below.

The body is a case. Thin bony plates, fused into a shell over the trunk and thin enough to be translucent, run down to a ventral edge sharp enough to have earned the family its other name, razorfish. Nothing in there bends. A shrimpfish is a blade with a spine on the back of it, which is an awkward mouthful for anything that tries, and the price of the armor is that the fish cannot flex to accelerate. The small clear fins do all the work and they do it slowly.

Slowly and vertically, snout toward the bottom, which is the thing everyone notices and the thing the species page here opens on. What is less well known is that the posture is not fixed. Pushed hard enough, a shrimpfish drops flat, runs horizontally like an ordinary fish for a few seconds, and is briefly unrecognizable as the same animal.

That terminal spine is also what splits the family in two. In the genus that lives in this sea it is jointed at its base and can be moved; in the other genus it is fused solid to the body, and that is the first thing checked by anyone trying to separate the two. One species is listed here, hand length including the snout, feeding the way its long-snouted relatives do, drawing single small animals up the tube into a mouth barely larger than they are.