Tantulocarida is a highly specialised group of

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s that consists of about 33

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

, treated as a

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

in superclass Multicrustacea. They are typically

ectoparasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

s that infest

copepod Copepods (; meaning 'oar-feet') are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (living in the water column), some are benthos, benthic (living on the sedimen ...

isopod Isopoda is an Order (biology), order of crustaceans. Members of this group are called isopods and include both Aquatic animal, aquatic species and Terrestrial animal, terrestrial species such as woodlice. All have rigid, segmented exoskeletons ...

s, tanaids,

amphipods Amphipoda () is an order (biology), order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods () range in size from and are mostly detritivores or scavengers. There are more than 10,700 amphip ...

and

ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...

Description

In the Tantulocarida, animals do not ever present eyes. The tantulus larvae has a head with a ventral oral disc but no appendages, a six-segmented thorax with six pairs of legs, and a limbless abdomen consisting of one to six segments in addition to a

telson The telson () is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ...

. The larvae also possesses a cuticular stylet on the cephalon through which they can push a rootlet system for extraction of nutrients from a host. The rootlet system itself is a direct extension of the gut.

Body length

Members of this subclass are minute – less than in length and have a dramatic reduction in body form compared to other

s, with an unsegmented, sac-like

thorax The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main di ...

and a much reduced

abdomen The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

. One tantulocarid species, ''Tantulacus dieteri'', is the world's smallest arthropod, with a total body length of only .

Life cycle

The tantulocarid life cycle is unique among crustaceans. The tantulus larva transforms directly from a non-feeding (lecithotrophic) and free-swimming organism into a parasite without any

instar An instar (, from the Latin '' īnstar'' 'form, likeness') is a developmental stage of arthropods, such as insects, which occurs between each moult (''ecdysis'') until sexual maturity is reached. Arthropods must shed the exoskeleton in order to ...

s. When entering the parasitic stage much of the body, such as the muscles, degenerates, even if the body itself becomes bigger. As a parasite it is permanently attached to its host, and after piercing its host's cuticle with an unpaired stylet, a rootlet system used to absorb nutrients enters through the hole and grow into the host’s tissue. The adult form develops inside the larva, and can become either a sac-like

parthenogenetic Parthenogenesis (; from the Greek + ) is a natural form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization. In animals, parthenogenesis means the development of an embryo from an unfertiliz ...

female, or a fully developed free-living, non-feeding and sexually-reproducing male or female. The eggs inside the parthenogenetic female are eventually released as fully developed tantulus larvae. The finding of what appears to be a benthic non-feeding nauplius larva suggests that eggs produced by sexual females hatch as nauplii instead of tantulus larvae. Both the parthenogenetic and sexual females are

semelparous Semelparity and iteroparity are two contrasting reproductive strategies available to living organisms. A species is considered ''semelparous'' if it is characterized by a single reproduction, reproductive episode before death, and ''iteroparous ...

Classification

Five

families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...

are recognised: Basipodellidae Boxshall & Lincoln, 1983: *'' Basipodella'' Becker, 1975 *'' Hypertantulus'' Ohtsuka & Boxshall, 1998 *'' Nipponotantulus'' Huys, Ohtsuka & Boxshall, 1994 *'' Polynyapodella'' Huys, Møberg & Kristensen, 1997 *'' Rimitantulus'' Huys & Conroy-Dalton, 1997 *'' Serratotantulus'' Savchenko & Kolbasov, 2009 *'' Stygotantulus'' Boxshall & Huys, 1989 Doryphallophoridae Huys, 1991: *'' Doryphallophora'' Huys, 1990 *'' Paradoryphallophora'' Ohtsuka & Boxshall, 1998 Microdajidae Boxshall & Lincoln, 1987: *'' Microdajus'' Greve, 1965 *'' Xenalytus'' Huys, 1991 Cumoniscidae Nierstrasz & Brender à Brandis, 1923 (formerly family Deoterthridae: *'' Amphitantulus'' Boxshall & Vader, 1993 *'' Aphotocentor'' Huys, 1991 *'' Arcticotantulus'' Kornev, Tchesunov & Rybnikov, 2004 *'' Boreotantulus'' Huys & Boxshall, 1988 *'' Campyloxiphos'' Huys, 1991 *'' Coralliotantulus'' Huys, 1991 *'' Cumoniscus'' Bonnier, 1903 *'' Deoterthron'' Bradford & Hewitt, 1980 *'' Dicrotrichura'' Huys, 1989 *'' Itoitantulus'' Huys, Ohtsuka Boxshall & Itô, 1992 *'' Tantulacus'' Huys, Andersen & Kristensen, 1992 Onceroxenidae Huys, 1991: *'' Onceroxenus'' Boxshall & Lincoln, 1987

References

External links

* {{Taxonbar, from=Q2340012 Maxillopoda Parasitic crustaceans Arthropod subclasses