Facetotecta
Encyclopedia
Facetotecta is a poorly known infraclass of thecostraca
n crustacean
s. The adult
forms have never been recognised, and the group is known only from its larvae
, the "y-nauplius" and "y-cyprid" larvae. They are mostly found in the north Atlantic Ocean
, neritic waters around Japan
, and the Mediterranean Basin
, where they also survive in brackish water.
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 barnacle
s. 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).
is relatively long, and also ornamented. In common with other thecostracans, Facetotecta pass through five naupliar instar
s before undergoing a single cyprid phase.
. A number of species have been described on the basis of a y-cyprid alone. As in barnacle
s, 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
.
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
.
s, some of which are likely to be inhabitants of coral reef
s.
Thecostraca
Thecostraca are a subclass of marine invertebrates containing about 1,320 described species. Many species have planktonic larvae which become sessile or parasitic as adults....
n crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s. The adult
Adult
An adult is a human being or living organism that is of relatively mature age, typically associated with sexual maturity and the attainment of reproductive age....
forms have never been recognised, and the group is known only from its larvae
Crustacean larvae
Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow...
, the "y-nauplius" and "y-cyprid" larvae. They are mostly found in the north Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, neritic waters around Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, and the Mediterranean Basin
Mediterranean Basin
In biogeography, the Mediterranean Basin refers to the lands around the Mediterranean Sea that have a Mediterranean climate, with mild, rainy winters and hot, dry summers, which supports characteristic Mediterranean forests, woodlands, and scrub vegetation...
, where they also survive in brackish water.
History
The German zoologist Christian Andreas Victor HensenVictor Hensen
Christian Andreas Victor Hensen was a German zoologist . He coined the term plankton and laid the foundation for biological oceanography....
first collected facetotectans from the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
in 1887, but assigned them to the copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
family Corycaeidae; later Hans Jacob Hansen
Hans Jacob Hansen
-References:*.-Literature:...
named them "y-nauplia", assuming them to be the larvae of unidentified barnacle
Barnacle
A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...
s. More recently, it has been suggested that, since there is a potential gap in the tantulocarid
Tantulocarida
Tantulocarida is a highly specialised group of parasitic crustaceans that consists of about 33 species, treated as a subclass of the class Maxillopoda . They are typically ectoparasites that infest copepods, isopods, tanaids, amphipods and ostracods...
life cycle
Biological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
, 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
Genetic analysis
Genetic analysis can be used generally to describe methods both used in and resulting from the sciences of genetics and molecular biology, or to applications resulting from this research....
using 18S ribosomal DNA
18S ribosomal RNA
18S ribosomal RNA is a part of the ribosomal RNA. The S in 18S represents Svedberg units. 18S rRNA is a component of the small eukaryotic ribosomal subunit...
reveal Facetotecta to be the sister group to the remaining Thecostraca
Thecostraca
Thecostraca are a subclass of marine invertebrates containing about 1,320 described species. Many species have planktonic larvae which become sessile or parasitic as adults....
(Ascothoracida
Ascothoracida
Ascothoracida is a small group of crustaceans, comprising around 100 species. They are found throughout the world, and are parasites on cnidarians and echinoderms....
and Cirripedia).
Nauplius
Y-nauplii are 250 um long, with a faceted cephalic shield, from which the group derives its name. The abdomenAbdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
is relatively long, and also ornamented. In common with other thecostracans, Facetotecta pass through five naupliar instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
s before undergoing a single cyprid phase.
Cyprid
The presence of a distinctive cyprid larva indicates that the Facetotecta is a member of the ThecostracaThecostraca
Thecostraca are a subclass of marine invertebrates containing about 1,320 described species. Many species have planktonic larvae which become sessile or parasitic as adults....
. A number of species have been described on the basis of a y-cyprid alone. As in barnacle
Barnacle
A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...
s, the cyprid is adapted
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
to seeking a place to settle as an adult. It has compound eyes, can walk using its antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
, and is capable of producing an adhesive glue
Adhesive
An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...
.
Juvenile
In 2008, a juvenile formJuvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
was produced by treating y-larvae with the hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
20-hydroxyecdysone
20-hydroxyecdysone
20-Hydroxyecdysone is a naturally occurring ecdysteroid hormone which controls the ecdysis and metamorphosis of arthropods. It is therefore one of the most common moulting hormones in insects, crabs, etc...
, which stimulated ecdysis
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
and the transition to the next life phase. The resulting animal, named the ypsigon, was slug-like, apparently unsegmented
Segmentation (biology)
Segmentation in biology refers to either a type of gastrointestinal motility or the division of some animal and plant body plans into a series of repetitive segments. This article will focus on the segmentation of animal body plans, specifically using the examples of the phyla Arthropoda,...
, and limbless
Arthropod leg
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa , trochanter , femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus ,...
.
Adults
While they have never been seen, the adult facetotectans are almost certainly endoparasites of other animalAnimal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s, some of which are likely to be inhabitants of coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s.
Species
Eleven species are currently recognised, while one species which is assigned to Hansenocaris – H. hanseni (Steuer, 1905) – is of uncertain affinities:- 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