Spectember 2023 #03: Raptorial Isopod

Modzilla07 asked for a “eurypterid or anomalocarid-esque isopod”:

A shaded sketch of a speculative swimming predatory isopod. Its shaped similarly to an extinct sea scorpion with a streamlines segmented body that ends in a fin-like horizontal tail fan. It has short antennae, a large pair of spiny grabbing front appendages similar to an anomalocarid, large compound eyes on short thick stalks, and two pairs of its legs are modified into long paddle-like structures.

Agriopterus modzillaseptenorum is descended from scavenger-predator intertidal cirolanids. At about 10cm long (~4″) it’s a giant compared to most other isopods, but not nearly as big as some of the radiodonts and eurypterids it convergently resembles.

Adapted for a free-swimming lifestyle, its second pair of antennae have been modified into spiny raptorial appendages and its first two pairs of legs have become flat swimming paddles. It’s a voracious little predator, usually snatching small fast-moving prey from the water and raking up soft-bodied animals from the seafloor – but groups will sometimes opportunistically swarm on much larger dead, dying, or injured targets.