Caught in passing

I was watching hermit crabs in the aquarium when a red worm zipped by.

Spiny polychaete. Each "foot" is tipped with a brush, and armed above with a long spine.

He's tiny; on the right, three copepods are playing. They're about a millimetre long. The round dots along the edge of the shell are oyster eyes. And I don't know what that yellow and black striped creature (or tentacle, or foot) is, peeking out from between the folds of the oyster shell.

A large isopod reached out from a seaweed clump to investigate a mass of green-centred bubbles, probably disintegrating algae.

These isopods are plentiful under rocks and clutching rockweed in the intertidal zone. Sometimes they come home with me; they live happily in the tank for a while, until a crab catches them for dinner. As long as there is at least one branch of rockweed, they stay out of reach.