Genus of crustaceans
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]
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]
Y-nauplius illustration
Y-cyprid illustration
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]
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]
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]
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]
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
^
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 .
hdl :
11250/2990967 .
^
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. Archived from
the original (PDF) on 2013-05-12. Retrieved 2009-12-14 .
^
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.