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.

Hymenocarines are characterized by the combination of 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[1]) and rounded mandibles and likely maxillae, post maxillae limbs with spiny, subdivided basis and endopods (lower, leg-like parts) with well-developed terminal claws; absence of appendages between antennae and mandibles; median sclerite and lobate protrusions located between compound eyes; 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).

[2][3] Based on the interpretation of simple head region that possess only a few segments and appendages, hymenocarine taxa were thought to be part of the upper stem-group euarthropods in early and mid 2010s.

[18][25][26][27] Chuandianella a bivalved arthropod morphologically similar to Waptia and long thought to be closely related[3][22] was reinterpreted as a non-hymenocarine euarthropod based on a restudy published in 2022, which found that it definitely lacked mandibles, characteristic of true hymenocarines.

[24] Cladogram of Hymenocarina, following Izquierdo-López and Caron, (2024):[1] Tuzoia Perspicaris Pectocaris Loricicaris Tokummia Branchiocaris Plenocaris Ercaicunia Clypecaris Pauloterminus Canadaspis Waptia Chuandianella Vermontcaris Odaraia Jugatacaris Fibulacaris Pakucaris Balhuticaris Nereocaris