CLASS THECOSTRACA GRUVEL, 1905

Diagnosis: Adapted from Høeg et al. (2009b). The taxon is monophyletic by molecular analyses, but see Petrunina, et al. (2014) on the possible inclusion of the Tantulocarida. No post-maxilular limb buds in nauplii; the larval development terminates with a cypridoid larva; the cypridoid with prehensile antennules is used in attachment; well-developed frontal filaments and compound eyes, whenever present, with three crystalline cones; the cypridoid larval carapace with five pairs of lattice organs.

Comment: Owing to the morphological diversity among the adults, the taxon can be diagnosed morphologically only by larval characters; those listed here are synapomorphic for the class; the adult stages are permanently sessile in the most of Ascothoracida and in all Cirripedia and are suspected to be so in Facetotecta .