Garden eelsCongridae

A garden eel does not leave home, and the word is close to literal. It feeds from its burrow, fights from its burrow, courts and spawns from its burrow, and there is no good record of a healthy adult crossing open sand to take up another one. Everything it does, it does with its tail still in the hole.

The hole is the only thing it builds. The eel works backward into the sand and lines the shaft with mucus from glands in the skin of its tail, cementing the grains into a tube that keeps its shape, and then it keeps that address. What stands out of the top is the front half of an eel, turned into the current, picking single copepods out of the water as they arrive. In stronger flow it leans further out, and a whole colony leans the same way, because a whole colony is reading the same water.

Even breeding is done without letting go. Neighbors sit at roughly the distance two eels can reach, and everything social happens across that gap: males stretch out and fight mouth to mouth with both tails anchored, and a male who has reached the female beside him wraps around her and spawns intertwined, eggs and sperm going straight into the current before the pair drop back into their own sand. That reach is why a colony looks planted rather than gathered.

The family is Congridae, which is otherwise a family of ordinary eels: the congers, heavy free-swimming hunters that work the bottom at night, two of which are listed here as well. Garden eels are the branch that stopped moving. The common one in this sea, Gorgasia sillneri, is known from nowhere else, and it stands in colonies of hundreds on the sand at the foot of reef slopes. Getting near them is the whole problem, and the method is unglamorous: arrive low, arrive slowly, then stop and wait longer than feels sensible.