The other day, I noticed a small translucent crustacean swimming frantically around a small rock pool, apparently trapped after being washed there at high tide. At first I thought it was a shrimp, but it’s something weirder.
It’s a hyperiid amphipod- a member of a group related to sandhoppers and scuds, but all members are fully pelagic and marine.
Many hyperiids have giant, translucent eyes with a sort of multifaceted retina inside. This guys’ dome- shaped head with a darker patch visible within is all eye.
Most species feed on salps or jellyfish- you might recognize the deep- sea genus Phronima from an episode of bbc’s Blue Planet.
(not my photo)
A more obscure but very large and bizarre- looking deep sea hyperiid, Cystisoma, takes both translucency and giant eyes to the extreme. The red spot is the aforementioned retina, which shows you just how much of this thing’s head is devoted to the eyes.
(also not my photo)
The one I found (1st pic) appears to be a member of the genus Themisto, which are both very abundant in temperate waters and somewhat unusual among huperiids in that they prey on smaller crustaceans such as copepods rather than gelatinous animals. You can’t see it very clearly in my picture, but their longer pairs of legs are mantis- like raptorial limbs, lined with spikes suited for snatching copepods out of the water.
Themisto libellula (not my photo)
