The abdomen consists of seven somites which decrease slightly in width towards the posterior.

The endopod is incompletely known, while the exopod is large and U-shaped, decreasing greatly in size near the posterior.

Arenosicaris is unusual among phyllocarid fossils for its preservation of limbs, if only partial.

[1] Arenosicaris's position is currently uncertain within Archaeostraca, although it may be somewhat related to the suborder Caryocaridina.

[2] Arenosicaris derives from arenosum, meaning "a sandy place" in reference to the unusual preservation in sand, and the Greek καρις, meaning "shrimp", a common crustacean suffix.