Facetotecta

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Facetotecta
Y-cyprid.png
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

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.[1] They are mostly found in the north Atlantic Ocean, neritic waters around Japan,[2] and the Mediterranean Basin, where they also survive in brackish water.[3]

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.[4] 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.[1] Genetic analysis using 18S ribosomal DNA reveal Facetotecta to be the sister group to the remaining Thecostraca (Ascothoracida and Cirripedia).[5]

Life cycle[edit]

Nauplius[edit]

Y-nauplii are 250–620 micrometres (0.010–0.024 in) long,[1] with a faceted cephalic shield, from which the group derives its name.[6] The abdomen is relatively long, and also ornamented.[1] In common with other thecostracans, Facetotecta pass through five naupliar instars before undergoing a single cyprid phase.[4]

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.[7] 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.[8]

Juvenile[edit]

In 2008, a juvenile form was produced by treating y-larvae with the hormone 20-hydroxyecdysone, which stimulated ecdysis and the transition to the next life phase. The resulting animal, named the ypsigon, was slug-like, apparently unsegmented, and limbless.[8][9]

Adults[edit]

While they have never been seen, the adult facetotectans are almost certainly endoparasites of other animals, some of which are likely to be inhabitants of coral reefs.[10]

Species[edit]

Eleven species are currently recognised,[2] while one species which is assigned to HansenocarisH. hanseni (Steuer, 1905) – is of uncertain affinities:[4]

References[edit]

  1. ^ a b c d Joel W. Martin & George E. Davis (2001). An Updated Classification of the Recent Crustacea (PDF). Natural History Museum of Los Angeles County. p. 132. 
  2. ^ a b Daphne Cuvelier (April 4, 2005). "Hansenocaris Itô, 1985". World Register of Marine Species. 
  3. ^ 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. 
  4. ^ a b c E. A. Ponomarenko (2006). "Facetotecta – Unsolved Riddle of Marine Biology". Russian Journal of Marine Biology 32 (Suppl. 1): S1–S10. doi:10.1134/S1063074006070017. 
  5. ^ 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. 
  6. ^ Christopher Taylor (February 23, 2008). "The secret of y-larvae". Catalogue of Organisms. 
  7. ^ 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. 
  8. ^ 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. 
  9. ^ 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. 
  10. ^ 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.