Things, all kinds, live in these marsh waters. Most I see are the usual small fish, insect critters and such.
There are also surprises in the pluff mud.
Crabs are here, in many places but not all. Depending on the dikes brackish water is common.
There are 3 foot (1 meter) long Sirens also. They are eel looking salamanders. Only the big predators mess with them. They fight back, and sometimes win.
And then you have this ‘whatever’. It could be a shrimp.
Maybe even part of a crawfish.
I don’t think it was eaten, just banged around a little. That means whatever it was proved to be very, very, nasty.