Hymenocarina
Hymenocarina is a group of extinct arthropods known from the Cambrian, they possess bivalved carapaces with exposed posteriors, and look superficially like shrimp. They are generally interpreted as stem-crustaceans or mandibulates. They were defined in Aria and Caron as: "Euarthropods with bivalved carapace covering cephalothoracic region up to a large portion of 27 post-cephalothoracic tagma; plesiomorphically, cephalothorax bearing well-developed antennules and enditic 28 endopod podomeres with well-developed terminal claws; limb basis segmented; posterior tagma with tergo-pleural 29 rings; tailpiece a rounded telson bearing well-developed caudal rami."
