Hymenocarina

Hymenocarina is an order of extinct marine arthropods known from the Cambrian. They possess bivalved carapaces, typically with exposed posteriors. Members of the group are morphologically diverse and had a variety of ecologies, including as filter feeders and as predators. Recent research has generally considered them to be stem or crown group members of Mandibulata, due to the presence of mandibles in well-preserved species.

== Description == Hymenocarines are characterized by the combination of the following characters: bivalved, convex carapace covering cephalothoracic (combined head and thorax) region; cephalothorax bearing multisegmented antennae (though as an exception antennae are absent in Odaraia) and rounded mandibles and likely maxillae, post maxillae limbs with spiny, subdivided basis and endopods (lower, leg-like braches of limbs) with well-developed terminal claws; absence of appendages between antennae and mandibles; median sclerite and lobate protrusions located between compound eyes; and posterior tagma (abdomen) with ring-like segments with the posterior of the body ending with pair of well-developed caudal rami (often in the form of tail flukes).