Ostracods ("seed shrimp") are minute
crustaceans, usually less than 1mm across,
smaller even than Moina, the mini daphnia. In a flash, ostracods
can completely withdraw into their hinged
protective lima-bean-shaped carapaces or
ostraca (Greek ostracon means "shell"), which are so hard
that many small fishes can't eat them. A
pair of sensitive swimming and grasping antennae
project at one end. Another pair is hidden
inside the shell. If daphnia hop, ostracods
scoot, using two pairs of legs to scrabble
nimbly over detritus and grains of sand.
They are harmless detritus feeders, usually
bouncing among gravel grains, but you'll
probably first notice them zipping around
near the water surface. Like other branchipods,
"seed shrimp" populations survive
droughts as dessicated cysts. They are just
part of the wider community in a planted
aquarium, and I don't discourage them, on
the general principle that diversity means
stability. In natural environments, dense
populations of ostracods are usually a symptom
of over-rich water.
Links.The Ostracod Research Group offers a good introduction to ostracods.
You'll find great color video stills there,
and the Introduction to ostracods gives you
basic anatomy. Their crunchy calcified cells
fossilize nicely, so you can get a hint of
their fossil history back to Cambrian or
Ordovician times, no less. And there are
some details of their sex life, or lack of
it. Because if your sex life is getting you down, remember that
there are certain lineages of parthenogenetic
ostracods that haven't had a date since the
Jurassic! Have a look at "Posters: Geographical
parthogenesis in European non-marine ostracods."
at that O.R.G. site.
...And if that's not enough, follow their
links to IRGO- the International Research
Group on Ostracoda.
