Anyone know what this critter is?

[mrWinter]

Noticed these guys in my sand bed and they are new. They caught my eye as rather large copepods or maybe rather small amphipods. They are benthic as far as I've seen, and motile, crawling on and in the sand. They were concentrated around a snail that I think is in the process of dying. Sucked a few up and put under the microscope expecting some little thing with a face, eyes and many legs and saw nothing of the sort. Looks like a clam with hair all over it. Perhaps it just moves with all those hairs? Not a problem or a pest, I'm just curious what has made itself a home in my tank.

 

[Steve and his Animals]

Could be a species of clam shrimp, relatives of water fleas that look like clams with legs and antennae poking out, but it's hard to say without seeing it open.

 

[WheatToast]

Could be a species of clam shrimp, relatives of water fleas that look like clams with legs and antennae poking out, but it's hard to say without seeing it open.

Might also be the superficially similar ostracod, a beneficial detritivore and one of the lesser-seen "pods."

 

[mrWinter]

Could be a species of clam shrimp, relatives of water fleas that look like clams with legs and antennae poking out, but it's hard to say without seeing it open.

I did not know such a thing existed, neat!

 

[mtfish]

Yep, clam shrimp is a common name for ostracods. And that is what you have.

 

[WheatToast]

Yep, clam shrimp is a common name for ostracods. And that is what you have.

Clam shrimp (which belong to the class Branchiopoda) are not the same as ostracods (class Ostracoda). Looking deeper into it, all clam shrimp are freshwater organisms, so what we are seeing here is an ostracod.

 

[mtfish]

I stand corrected. Different classes. Got confused in my memories of clam shrimp vs seed shrimp.

Here is too much information.

Members of the three crustacean classes Cladocera, Ostracoda and Conchostraca have a bivalved carapace covering the whole body. This makes them look superficially like bivalved molluscs. Identification to Crustacea can be based on the form of the body inside the shell or carapace: bivalved molluscs have a soft, unsegmented body; crustaceans have a segmented body bearing several pairs of legs, gills, swimming organs or feathery filter-feeding structures.

The Cladocera (water fleas) are generally very small but some species reach 5-6 mm. The bivalved carapace covers the body but the head is free. Distribution is Australia-wide. Of the three crustacean classes with bivalved carapaces these are the least likely to be mistaken for bivalved molluscs.

The Conchostraca (clam shrimps) are small to medium size (up to 25mm), generally green, green-blue or brown,and often translucent. They have several to many trunk appendages and the second antennae protrude from the carapace. They are found in lakes, dams, ponds and temporary pools and are widespread across Australia and can more readily be confused.

The Ostracoda (mussel shrimps, seed shrimps) resemble Conchostraca but are usually somewhat smaller. The carapace is generally translucent and may be notched in outline and/or carry complex patterns of knobs, pores or hairs. Both the first and second antennae are long , setose and may protrude from the carapace.