The carapace is approximately twice as long as it is high, and in the male, which has a rounded pseudorostrum, rather smooth.

The female has two to six small serrations in the middle of the dorsal ridge of the carapace, and a sharply leading pseudorostrum.

I. trispinosa are usually found in fine sand beaches, such as those formed by silt deposits.

They prefer shallower depths, but may be found as deep as 150 m. During summer nights the males emerge from sand, swarming to the surface, frequently attracted by light.

[2] They are found from Norway to the Moroccan coast, around the Canary Islands and in the Mediterranean Sea.