-- The hermit crabs, first. I have 10 hermits in my tank, mostly grainy hand hermits (like the one below) and a few hairy hermits. They're easily distinguished; the grainy hands have red antennae and the hairies have black and white legs and antennae.
A couple of days ago, three of them molted the same day; one hairy hermit, two grainy hands. Yesterday, another, a hairy hermit. I found this guy wandering around without a shell. This afternoon, the latest hairy hermit to molt was doing the same.
I rarely catch one molting, and even more rarely wandering around nude. Why the rush, all of a sudden?
-- The shrimps. There are 3, as far as I know. One very small one, transparent, a medium sized shrimp, greenish and transparent, just barely starting to develop black lines. And this one, about half an inch long. I had tentatively identified it as a coonstripe shrimp, but now that its pattern is more developed, I see that it's a Sitka Coastal shrimp, Heptacarpus sitchensis. They should grow to about 1.1 inches long.
The encyclopedia says they change colour to match the seaweed. Possibly they do; I don't see them very often, and that may be the reason. But I've never caught this large one wearing green.
-- Snails. I don't know when or how these arrived in the tank. There were three, but the flatworms ate one. The two remaining were really tiny when I first saw them. They move slowly from barnacle to barnacle, staying a day or three on each one, feeding. (I'm running out of live barnacles; memo: pick up a barnacled rock next visit to the beach.)
I am amazed at how quickly they grow. They're like weeds. I can see the change in them from day to day. In a few short weeks, this one has stretched to almost an inch. Snails grow, not by swelling and stretching, like we do, but by adding new segments at the bottom, each one a bit larger. This turn of the spiral is as long on its own as the whole previous shell. Eyeballing it, I think each coil more or less follows that rule. So the larger it is, the faster it grows? I'm going to have to start measuring them.
They're some sort of trophon, as far as I can see. They have the ribs, the squared-off coils, and the long canal at the lower end. I saw one on the glass for the first time today; the foot is round and white.
-- When I clean out the filter every three days, I usually double-check the gunk that I wash out of it; I found that amphipods and small snails sometimes shelter inside the sponge itself. I try to remove the larger ones, and return them to the tank; I've seen the crabs catch the amphipods for food.
Often, I find these. They're tiny and completely transparent; more transparent than the water, often. Under the hand lens, with the light at the right angle, I see them as delicate fans with some kind of handle at the bottom. I thought they might be some kind of hydroid, but I couldn't be sure without seeing the "handle".
Last night, trying to find some way to show them to Laurie, I hit upon the idea of dyeing them. I have a small bottle of methylene blue; a drop of that on each one worked perfectly. This one, fully stretched out, is 1/4 inch long.
They look, now, more like a barnacle out of its shell. A sharply angled body, long, branched cirripeds, short, branched mouth parts (maybe), and is that an eye? Shouldn't be, on a barnacle. Some sort of crustacean, then.
In a drop of water, to allow a three-dimensional view.
The cirri. They look much like the barnacle's feet.
-- One more. These turned up in the gunk out of the filter, too. They look like copepods, but they don't move right; they slither along like slugs, instead of darting here and there. But they're not much bigger than the little one-eyed copepods. Too small to photograph, and even with the microscope, they're not that easy to see. They're like a smooth, milky droplet, with two long, dark eyes at the broad end. Nothing more, except that they stretch out when they move, and return to the fat, round shape when they stop. Occasionally, they lift their heads towards the light. They can swim, but prefer to stay on the bottom, sliding along the surface of the detritus there.
I had to draw them; there's not much to photograph. Easy drawing, though; I included all the details I could see.
And they are so cute! They look, to me, like shmoos. (Remember them?) So that's what I'm calling them until someone, somewhere, gives me a hint where to look for the correct name.