Spotty amphipod

In any clump of seaweed from our beaches, whether it comes from the intertidal zone or from the piles of rotting debris above the tide line, a handful will almost always contain amphipods. Some, brought home with sea lettuce and eelgrass for the hermit crabs, will swim madly about when placed again in water. Some, collected from the borderline zone, do swim, but are inclined to jump out of the water if they are disturbed, and hop all over the counter and the floor, causing me to chase them down in a breathless mad scramble. They are fine once they get into the aquarium, away from fumbling human hands.

These ones tend to be bigger than the intertidal amphipods, and usually darker, sometimes green, sometimes brown. The eelgrass dwellers come in all sizes, from tiny green ones to transparent babies, a millimetre or less in length.

An extra large amphipod has been swimming around the aquarium for the last few months, getting larger by the day, it seems. And I can't decide what colour he is. In some lights, he looks dark brown; at other times, he's almost orange. Or he's a dark green. He's always speckled, though, in any light.

The smaller ones are breeding madly, but this one doesn't join the festivities; he's a separate species, and has no mate.

I found him resting close to the glass wall, and got a few photos before he took off again. This time, he seems to have green highlights.

Spotty amphipod, about 1 cm. long

Amphipods never stop moving, even at rest. In the curve of their belly, a mass of appendages flutters constantly, stirring the water, aerating the gills. Even on the larger ones, it's hard even to focus my eyes on them. In this photo, though, there's a hint of cross-hatched paddles in between the "legs". (Front to tail, they're called gnathopods, pereopods, then pleiopods, and uropods, with a telson at the end.)

Abdominal appendages, showing gills

This may be the same one, back in February.