Biology:Facetotecta
| Facetotecta | |
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| A Y-psigon escaping from its y-cyprid | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Thecostraca |
| Subclass: | Facetotecta Grygier, 1985 |
| Family: | Hansenocarididae Itô, 1985 |
| Genus: | Hansenocaris Itô, 1985 |
| Species | |
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See text | |
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
Y-nauplius illustration
Y-cyprid illustration
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.
- ↑ 2.0 2.1 2.2 2.3 Joel W. Martin; George E. Davis (2001). An Updated Classification of the Recent Crustacea. Natural History Museum of Los Angeles County. pp. 132. http://atiniui.nhm.org/pdfs/3839/3839.pdf.
- ↑ 3.0 3.1 Daphne Cuvelier (April 4, 2005). "Hansenocaris Itô, 1985". World Register of Marine Species. http://www.marinespecies.org/aphia.php?p=taxdetails&id=150307.
- ↑ 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.
- ↑ 5.0 5.1 5.2 E. A. Ponomarenko (2006). "Facetotecta – Unsolved Riddle of Marine Biology". Russian Journal of Marine Biology 32 (Suppl. 1): S1–S10. doi:10.1134/S1063074006070017.
- ↑ 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:ROTRAT2.0.CO;2].
- ↑ Christopher Taylor (February 23, 2008). "The secret of y-larvae". Catalogue of Organisms. http://catalogue-of-organisms.blogspot.com/2008/02/secret-of-y-larvae.html.
- ↑ 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". Raffles Bulletin of Zoology 55 (2): 343–353. http://rmbr.nus.edu.sg/rbz/biblio/55/55rbz343-353.pdf.
- ↑ 9.0 9.1 Gerhard Scholtz (2008). "Zoological detective stories: the case of the facetotectan crustacean life cycle". Journal of Biology 7 (5): 16. doi:10.1186/jbiol77. PMID 18598383. PMC 2447532. http://jbiol.com/content/7/5/16.
- ↑ 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. 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". 10th International Coral Reef Symposium. Okinawa, Japan. http://wwwsoc.nii.ac.jp/jcrs/icrs2004/img/07poster_239-298.pdf.
Wikidata ☰ Q137276 entry
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