[4] The German zoologist Christian Andreas Victor Hensen first collected facetotectans from the North Sea in 1887 but assigned them to the copepod family Corycaeidae; later Hans Jacob Hansen named them "y-nauplia", assuming them to be the larvae of unidentified barnacles.

[2] Genetic analysis using 18S ribosomal DNA reveal Facetotecta to be the sister group to the remaining Thecostraca (Ascothoracida and Cirripedia).

[6] Y-nauplii are 250–620 micrometres (0.010–0.024 in) long,[2] with a faceted cephalic shield, from which the group derives its name.

[2] In common with other thecostracans, Facetotecta pass through five naupliar instars before undergoing a single cyprid phase.

[9] In 2008, a juvenile form was artificially produced by treating y-larvae with the hormone 20-hydroxyecdysone, which stimulated ecdysis and the transition to a new life phase.