Facetotecta is a poorly known subclass ofthecostracancrustaceans.[1] Theadult forms have never been recognized, and the group is known only from itslarvae, the "y-nauplius" and "y-cyprid" larvae.[2] The only known genus isHansenocaris and the familyHansenocarididae. They are mostly found in the northAtlantic Ocean,neritic waters aroundJapan,[3] and theMediterranean Basin, where they also survive in brackish water.[4]
Y-nauplii are 250–620 micrometres (0.010–0.024 in) long,[2] with a facetedcephalic shield, from which the group derives its name.[7] Theabdomen is relatively long, and also ornamented.[2] In common with other thecostracans, Facetotecta pass through five naupliarinstars before undergoing a single cyprid phase.[5]
The presence of a distinctivecyprid larva indicates that the Facetotecta is a member of theThecostraca. A number of species have been described on the basis of a y-cyprid alone.[8] As inbarnacles, the cyprid isadapted to seeking a place to settle as an adult. It hascompound eyes, canwalk using itsantennae, and is capable of producing anadhesive glue.[9]
Eleven species are currently recognised,[3] while one species which is assigned toHansenocaris –H. hanseni(Steuer, 1905) – is of uncertain affinities:[5]
^Genuario Belmonte (2005). "Y-nauplii (Crustacea, Thecostraca, Facetotecta) from coastal waters of the Salento Peninsula (south eastern Italy, Mediterranean Sea) with descriptions of four new species".Marine Biology Research.1 (4):254–266.doi:10.1080/17451000500202518.S2CID208372852.
