Facetotecta
{{Short description|Genus of crustaceans}}
{{Automatic taxobox
| image = 12915 2008 Article 174 Fig5 HTML.png
| image_caption = A Y-psigon escaping from its y-cyprid
| display_parents = 2
| grandparent_authority = Grygier, 1985
| parent_authority = Itô, 1985
| taxon = Hansenocaris
| authority = Itô, 1985
| subdivision_ranks = Species
| subdivision = See text
}}
Facetotecta is a poorly known subclass of thecostracan crustaceans. The adult forms have never been recognized, and the group is known only from its larvae, the "y-nauplius" and "y-cyprid" larvae.{{cite book |url=http://atiniui.nhm.org/pdfs/3839/3839.pdf |title=An Updated Classification of the Recent Crustacea |author1=Joel W. Martin |author2=George E. Davis |year=2001 |pages=132 |publisher=Natural History Museum of Los Angeles County |access-date=2009-12-14 |archive-date=2013-05-12 |archive-url=https://web.archive.org/web/20130512091254/http://atiniui.nhm.org/pdfs/3839/3839.pdf |url-status=dead }} The only known genus is Hansenocaris and the family Hansenocarididae. They are mostly found in the north Atlantic Ocean, neritic waters around Japan, and the Mediterranean Basin, where they also survive in brackish water.{{cite journal |title=Y-nauplii (Crustacea, Thecostraca, Facetotecta) from coastal waters of the Salento Peninsula (south eastern Italy, Mediterranean Sea) with descriptions of four new species |author=Genuario Belmonte |doi=10.1080/17451000500202518 |journal=Marine Biology Research |volume=1 |issue=4 |year=2005 |pages=254–266|s2cid=208372852 }}
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. 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).{{cite journal |journal=Journal of Crustacean Biology |volume=22 |issue=3 |pages=661–669 |year=2002 |doi=10.1651/0278-0372(2002)022[0661:ROTRAT]2.0.CO;2 |title=Reanalysis of the relationships among the Cirripedia and the Ascothoracida and the phylogenetic position of the Facetotecta (Maxillopoda: Thecostraca) using 18S rDNA sequences |author1=Marcos Pérez-Losada |author2=Jens T. Høeg |author3=Gregory A. Kolbasov |author-link4=Keith A. Crandall|author4=Keith A. Crandall |s2cid=84126659 }}
Life cycle
Y-nauplius.png|Y-nauplius illustration
Y-cyprid.png|Y-cyprid illustration
=Nauplius=
Y-nauplii are {{convert|250|-|620|um|in|3}} long, with a faceted cephalic shield, from which the group derives its name.{{cite web |url=http://catalogue-of-organisms.blogspot.com/2008/02/secret-of-y-larvae.html |author=Christopher Taylor |work=Catalogue of Organisms |title = The secret of y-larvae |date=February 23, 2008}} 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.
=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.{{cite journal |journal=Raffles Bulletin of Zoology |year=2007 |volume=55 |issue=2 |pages=343–353 |title=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 |author1=Gregory A. Kolbasov |author2=Mark J. Grygier |author3=Viatcheslav V. Ivanenko |author4=Alejandro A. Vagelli |url=http://rmbr.nus.edu.sg/rbz/biblio/55/55rbz343-353.pdf}} 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.
=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 y-psigon, was slug-like, apparently unsegmented, and limbless.{{cite journal |title=Zoological detective stories: the case of the facetotectan crustacean life cycle |author=Gerhard Scholtz |journal=Journal of Biology |year=2008 |volume=7 |pages=16 |doi=10.1186/jbiol77 |pmc=2447532 |pmid=18598383 |issue=5 |doi-access=free }}{{cite journal |title=Induced metamorphosis in crustacean y-larvae: Towards a solution to a 100-year-old riddle |author1=Henrik Glenner |author2=Jens T. Høeg |author3=Mark J. Grygier |author4=Yoshihisa Fujita |journal=BMC Biology |year=2008 |volume=6 |pages=21 |doi=10.1186/1741-7007-6-21 |pmid=18492233 |url= |pmc=2412843 |doi-access=free }}
=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.{{cite conference|title=Introduction to the tremendous diversity of y-larvae (Crustacea: Maxillopoda: Thecostraca: Facetotecta) in inshore coral reef plankton at Sesoko Island, Okinawa, Japan |author1=Mark Grygier |author2=Jens T. Høeg |author3=Yoshihisa Fujita |series=Biodiversity and Diversification in the Indo-West Pacific |conference=10th International Coral Reef Symposium |date=July 2004 |location=Okinawa, Japan |url=http://wwwsoc.nii.ac.jp/jcrs/icrs2004/img/07poster_239-298.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110611232905/http://wwwsoc.nii.ac.jp/jcrs/icrs2004/img/07poster_239-298.pdf |archive-date=2011-06-11 }}
Species
Eleven species are currently recognised,{{cite web |url=http://www.marinespecies.org/aphia.php?p=taxdetails&id=150307 |title=Hansenocaris Itô, 1985 |author=Daphne Cuvelier |date=April 4, 2005 |publisher=World Register of Marine Species}} while one species which is assigned to Hansenocaris – H. hanseni (Steuer, 1905) – is of uncertain affinities:{{cite journal |title=Facetotecta – Unsolved Riddle of Marine Biology |author=E. A. Ponomarenko |journal=Russian Journal of Marine Biology |volume=32 |issue=Suppl. 1 |pages=S1–S10 |year=2006 |doi=10.1134/S1063074006070017|bibcode=2006RuJMB..32S...1P |s2cid=2943845 }}
{{div col|colwidth=23em}}
- 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
{{div col end}}
References
{{Reflist|refs=
{{Cite journal
| title = The evolutionary diversity of barnacles, with an updated classification of fossil and living forms
| date = 2021
| last1 = Chan | first1 = Benny K. K.
| last2 = Dreyer | first2 = Niklas
| last3 = Gale | first3 = Andy S.
| last4 = Glenner | first4 = Henrik
| last5 = Ewers-Saucedo | first5 = Christine
| last6 = Pérez-Losada | first6 = Marcos
| last7 = Kolbasov | first7 = Gregory A.
| last8 = Crandall | first8 = Keith A.
| last9 = Høeg | first9 = Jens T.
| display-authors = 4
| journal = Zoological Journal of the Linnean Society
| volume = 193
| issue = 3
| pages = 789–846
| doi = 10.1093/zoolinnean/zlaa160| doi-access = free
| hdl = 11250/2990967
| hdl-access = free
}}
}}
{{Taxonbar|from=Q137276}}