Facetotecta

Superregnum: Eukaryota
Cladus: Unikonta
Cladus: Opisthokonta
Cladus: Holozoa
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Protostomia
Cladus: Ecdysozoa
Cladus: Panarthropoda
Phylum: Arthropoda
Subphylum: Crustacea
Superclassis: Multicrustacea
Classis: Thecostraca
Infraclassis: Facetotecta
Familiaː Hansenocarididae
Name

Facetotecta Grygier, 1985ː

References

Template:Grygier, 1985

Olesen, J. & Grygier, M.J. 2022. Two new species of lecithotrophic nauplius y with remarkable labra from Okinawa, Japan, and a family-group name for y-larvae (Crustacea: Thecostraca: Facetotecta: Hansenocarididae fam. nov.). Species Diversity 27ː 301–317. Open access DOI: 10.12782/specdiv.27.301 Reference page.

Taxon identifiers

Wikidata: Q137276 Fossilworks: 133216 iNaturalist: 473797 NCBI: 116173 WoRMS: 150305

Vernacular names
中文: 带甲下纲

Facetotecta is a poorly known subclass of thecostracan crustaceans.[1] The adult forms have never been recognised, and the group is known only from its larvae, the "y-nauplius" and "y-cyprid" larvae.[2] They are mostly found in the north Atlantic Ocean, neritic waters around Japan,[3] and the Mediterranean Basin, where they also survive in brackish water.[4]
History

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.[5] 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.[2] Genetic analysis using 18S ribosomal DNA reveal Facetotecta to be the sister group to the remaining Thecostraca (Ascothoracida and Cirripedia).[6]
Life cycle
Nauplius

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.[7] The abdomen is relatively long, and also ornamented.[2] In common with other thecostracans, Facetotecta pass through five naupliar instars before undergoing a single cyprid phase.[5]
Cyprid

The presence of a distinctive cyprid larva indicates that the Facetotecta is a member of the Thecostraca. A number of species have been described on the basis of a y-cyprid alone.[8] As in barnacles, the cyprid is adapted to seeking a place to settle as an adult. It has compound eyes, can walk using its antennae, and is capable of producing an adhesive glue.[9]
Juvenile

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. The resulting animal, named the ypsigon, was slug-like, apparently unsegmented, and limbless.[9][10]
Adults

While they have never been seen, the adult facetotectans may be endoparasites of other animals, some of which could be inhabitants of coral reefs.[11]
Species

Eleven species are currently recognised,[3] while one species which is assigned to Hansenocaris – H. hanseni (Steuer, 1905) – is of uncertain affinities:[5]

Hansenocaris acutifrons Itô, 1985
Hansenocaris corvinae Belmonte, 2005
Hansenocaris furcifera Itô, 1989
Hansenocaris itoi Kolbasov & Høeg, 2003
Hansenocaris leucadea Belmonte, 2005
Hansenocaris mediterranea Belmonte, 2005
Hansenocaris pacifica Itô, 1985
Hansenocaris papillata Kolbasov & Grygier, 2007
Hansenocaris rostrata Itô, 1985
Hansenocaris salentina Belmonte, 2005
Hansenocaris tentaculata Itô, 1986

References

Chan, Benny K. K.; Dreyer, Niklas; Gale, Andy S.; Glenner, Henrik; et al. (2021). "The evolutionary diversity of barnacles, with an updated classification of fossil and living forms". Zoological Journal of the Linnean Society. 193 (3): 789–846. doi:10.1093/zoolinnean/zlaa160.
Joel W. Martin; George E. Davis (2001). An Updated Classification of the Recent Crustacea (PDF). Natural History Museum of Los Angeles County. p. 132.
Daphne Cuvelier (April 4, 2005). "Hansenocaris Itô, 1985". World Register of Marine Species.
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. S2CID 208372852.
E. A. Ponomarenko (2006). "Facetotecta – Unsolved Riddle of Marine Biology". Russian Journal of Marine Biology. 32 (Suppl. 1): S1–S10. doi:10.1134/S1063074006070017. S2CID 2943845.
Marcos Pérez-Losada; Jens T. Høeg; Gregory A. Kolbasov; Keith A. Crandall (2002). "Reanalysis of the relationships among the Cirripedia and the Ascothoracida and the phylogenetic position of the Facetotecta (Maxillopoda: Thecostraca) using 18S rDNA sequences". Journal of Crustacean Biology. 22 (3): 661–669. doi:10.1651/0278-0372(2002)022[0661:ROTRAT]2.0.CO;2. S2CID 84126659.
Christopher Taylor (February 23, 2008). "The secret of y-larvae". Catalogue of Organisms.
Gregory A. Kolbasov; Mark J. Grygier; Viatcheslav V. Ivanenko; Alejandro A. Vagelli (2007). "A new species of the y-larva genus Hansenocaris Itô, 1985 (Crustacea: Thecostraca: Facetotecta) from Indonesia, with a review of y-cyprids and a key to all their described species" (PDF). Raffles Bulletin of Zoology. 55 (2): 343–353.
Gerhard Scholtz (2008). "Zoological detective stories: the case of the facetotectan crustacean life cycle". Journal of Biology. 7 (5): 16. doi:10.1186/jbiol77. PMC 2447532. PMID 18598383.
Henrik Glenner; Jens T. Høeg; Mark J. Grygier; Yoshihisa Fujita (2008). "Induced metamorphosis in crustacean y-larvae: Towards a solution to a 100-year-old riddle". BMC Biology. 6: 21. doi:10.1186/1741-7007-6-21. PMC 2412843. PMID 18492233.
Mark Grygier; Jens T. Høeg; Yoshihisa Fujita (July 2004). Introduction to the tremendous diversity of y-larvae (Crustacea: Maxillopoda: Thecostraca: Facetotecta) in inshore coral reef plankton at Sesoko Island, Okinawa, Japan (PDF). 10th International Coral Reef Symposium. Biodiversity and Diversification in the Indo-West Pacific. Okinawa, Japan. Archived from the original (PDF) on 2011-06-11.