Misophrioida

A small but evolutionarily significant order of the subclass Copepoda, containing only a few species. Misophrioids have two subdivisions of the body, the anterior prosome and posterior urosome, articulated immediately behind the fifth thoracic somite. This feature immediately distinguishes misophrioids from calanoids. Like calanoids, some misophrioids have a dorsal heart, a character that distinguishes the taxon from both cyclopoids and harpacticoids. The misophrioids have four unique characteristics: a carapacelike posterior extension of the head region (cephalosome) that encloses the first leg-bearing segment; the absence of the nauplius eye in all life stages; the retention of the antennary gland as the functional excretory system of adults; and a single naupliar developmental stage.

The unique characteristics of the misophrioids are interpreted as having resulted from the adaptation to a bathypelagic mode of life and gorging as a feeding strategy. However, species of three newly described genera also exhibit a number of characteristics that approach those attributed to a hypothetical copepod ancestor. See also Calanoida; Copepoda; Crustacea; Cyclopoida; Harpacticoida.