I never would have imagined that one day I would be handing out treats for worms.
I have at least three fair-sized polychaetes, probably sea nymphs, living in the sand at the bottom of the aquarium. I don't usually see them, unless I empty the tank and comb through their hiding places. In the last couple of weeks, I've done that twice; once in a periodic cleanup, and once because Big Green, the crab, made such a mess of the place. Each time, the nymphs have had to make themselves new burrows, and, as luck would have it, a couple ended up right beside the glass.
I caught the biggest sticking his nose out of the sand, stretching and waving around, as if sniffing for food. When I moved, and my shadow fell on him, he shrunk back into cover instantly. I polished off the glass and waited; after a bit, the cirri (long tentacle-like face decorations) poked through the sand, then the face followed. Slither, slither, left, right, straight ahead, over a rock, always leaving the bulk of his length securely inside the tunnel. When a hermit crab came near, he reacted even faster than he had before; a quick convulsion and he was gone.
He was greedy, and came back for more several times, enough for me to get these photos.
Friday, when I re-organized the tank again, three much smaller worms ended up near the glass. These are ones I had not seen before, except maybe as tiny red hairs. Now they are about as thick as a pencil lead. And they are out looking for food.
I was wondering, earlier, what they eat. Kozloff says they are algae eaters, but other researchers call them predators. These ones, at least, are meat eaters, whether as scavengers or predators on live animals, I can't tell.
These aren't the only worms in the tank; doing the last tidying up, I removed a shell where one of the flatworms was hiding. After I refilled the aquarium and all was at peace, he was wandering around on the glass.
When I brought these home, six weeks ago, they were about 6 or 7 mm., just over 1/4 inch, long. Now this one is as long as the first joint of my thumb, almost 3 cm, or over an inch. It must be getting enough to eat. I wonder what that is.
He slip-slid all the way around the tank, roaming from the top to the bottom, then back again. Eventually, he came across this big black-tailed barnacle. I watched as he left the glass and flowed over the rough shell. ( I wondered how that felt; didn't it scratch his tender flesh? Guess not.) He came to the lip, flowed over it, covering the mouth, then slid farther down between the plates and completely disappeared.
Do these flatworms eat polychaetes? Do they eat barnacles?