11-543: See text Facetotecta is a poorly known subclass 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. They are mostly found in the north Atlantic Ocean , neritic waters around Japan , and the Mediterranean Basin , where they also survive in brackish water. The German zoologist Christian Andreas Victor Hensen first collected facetotectans from
22-494: 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 . While they have never been seen, the adult facetotectans may be endoparasites of other animals , some of which could be inhabitants of coral reefs . Eleven species are currently recognised, while one species which
33-602: A modified integument of the carapace. More basal forms are ectoparasitic, but most genera are meso- and endoparasitic. The sexes are separate, except from secondary hermaphroditic species of the Petrarcidae. In many species the larger female often have smaller males living inside her mantle cavity. Ascothoracida was previously ranked as an order within the infraclass Cirripedia ( barnacles ), but now both Ascothoracida and Cirripedia are considered separate subclasses . Those two subclasses, along with Facetotecta , make up
44-528: A single cyprid phase. 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. 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 . In 2008,
55-558: A single genus, Hansenocaris , known only from the tiny planktonic nauplii called "y-larvae". These larvae have no known adult form, though it is suspected that they are parasites, and their affinity is uncertain. Some researchers believe that they may be larval tantulocaridans . No larval tantulocaridans are currently known. The group Ascothoracida contains about 110 species, all parasites of coelenterates and echinoderms . The nauplius larvae (sometimes absent) can be both lecithotrophic (non-feeding) and planktotrophic (feeding), and
66-494: Is a small group of parasitic marine crustaceans , comprising around 100 species and divided into Dendrogastrida and Laurida. They are found throughout the world on cnidarians and echinoderms . Dendrogastrida are parasites on echinoderms, and Laurida are parasites on cnidarians, except from the species Waginella Grygier, which is also a parasite on echinoderms ( crinoids ). Piercing and sucking mouthparts are used for feeding, and more advanced forms also absorb nutrients through
77-463: Is assigned to Hansenocaris – H. hanseni (Steuer, 1905) – is of uncertain affinities: Thecostraca Thecostraca is a class of marine invertebrates containing over 2,200 described species. Many species have planktonic larvae which become sessile or parasitic as adults . The most prevalent subgroup are the barnacles (subclass Cirripedia), constituting a little over 2,100 known species. The subgroup Facetotecta contains
88-623: Is followed by a larval stage called the cyprid, which is always lecithotrophic. The cypridoid larvae are referred to as the y-cyprid in the Facetotecta, the a-cyprid in the Ascothoracida , and the c-cyprid, or just cyprid, in the Cirripedia. This article follows Chan et al. (2021) and the World Register of Marine Species in placing Thecostraca as a class of Crustacea and in the following classification of thecostracans down to
99-472: 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 . 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
110-490: 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 ). Y-nauplii are 250–620 micrometres (0.010–0.024 in) long, with a faceted cephalic shield , from which the group derives its name. The abdomen is relatively long, and also ornamented. In common with other thecostracans, Facetotecta pass through five naupliar instars before undergoing
121-870: The level of orders. Previously, Thecostraca was considered a subclass of Maxillopoda . Significant changes in the organization of Cirripedia's orders, families, and genera were introduced in 2021 by Chan et al. and accepted by the World Register of Marine Species. Class Thecostraca Gruvel , 1905 The following cladogram depicts the internal relationships of the Thecostraca as of 2021. Facetotecta Laurida Dendrogastrida Cryptophialida Lithoglyptida Iblomorpha Eolepadomorpha † Archaeolepadomorpha † Pollicipedomorpha Calanticomorpha Scalpellomorpha Brachylepadomorpha † Verrucomorpha Balanomorpha Rhizocephala Ascothoracida Dendrogastrida Grygier, 1987 Laurida Grygier, 1987 Ascothoracida
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