Facetotecta
| Facetotecta | |
|---|---|
 |
|
| Y-cyprid | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Crustacea |
| Class: | Maxillopoda |
| Subclass: | Thecostraca |
| Infraclass: |
Facetotecta Grygier, 1985 |
| Family: |
Hansenocarididae Itô, 1985 |
| Genus: |
Hansenocaris Itô, 1985 |
| Species | |
|
See text |
|
See text
Facetotecta is a poorly known infraclass of thecostracan crustaceans. The adult forms have never been recognised, and the group is known only from its larvae, the "y-nauplius" and "y-cyprid" larvae. They are mostly found in the north Atlantic Ocean, neritic waters around Japan, and the Mediterranean Basin, where they also survive in brackish water.
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. More recently, it has been suggested that, since there is a potential gap in the tantulocarid life cycle, y-larvae may be the larvae of tantulocarids. However, this would be "a very tight fit", and it is more likely that the adult forms have not yet been seen.Genetic analysis using 18S ribosomal DNA reveal Facetotecta to be the sister group to the remaining Thecostraca (Ascothoracida and Cirripedia).
Y-nauplii are 250–620 micrometres (0.010–0.024 in) long, with a faceted cephalic shield, from which the group derives its name. The abdomen is relatively long, and also ornamented. In common with other thecostracans, Facetotecta pass through five naupliar instars before undergoing a single cyprid phase.
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