Tethyan-reliction
Guides
Thecostraca
Barnacles and Allies
Thecostraca is a class of marine crustaceans encompassing over 2,200 described species, with barnacles (subclass Cirripedia) comprising the vast majority. The group includes three major lineages: sessile suspension-feeding barnacles, parasitic ascothoracidans that infect cnidarians and echinoderms, and the enigmatic Facetotecta, known only from planktonic larvae. Members undergo distinctive larval development, typically featuring a nauplius stage followed by a cypris stage that facilitates settlement. Thecostraca exhibits remarkable life history diversity, ranging from free-living suspension feeders to endoparasites with highly derived morphologies.