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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
[ edit ]
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
[ edit ]
Y-nauplius illustration
Y-cyprid illustration
Nauplius
[ edit ]
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
[ edit ]
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
[ edit ]
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
[ edit ]
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
[ edit ]
Eleven species are currently recognised,[3] while one species which is assigned to Hansenocaris – H. hanseni (Steuer, 1905) – is of uncertain affinities:[5]
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
[ edit ]
^ a b 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 .
^ a b c E. A. Ponomarenko (2006). "Facetotecta – Unsolved Riddle of Marine Biology". Russian Journal of Marine Biology . 32 (Suppl. 1): S1–S10. Bibcode :2006RuJMB..32S...1P . 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.
^ a b 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.
R e t r i e v e d f r o m " https://en.wikipedia.org/w/index.php?title=Facetotecta&oldid=1218560606 "
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