Tantulocarida

Tantulocarida is a highly specialised group of parasitic crustaceans that consists of about 33 species, treated as a class in superclass Multicrustacea. They are typically ectoparasites that infest copepods, isopods, tanaids, amphipods and ostracods.^[2][3]

Tantulocarida
Microdajus sp.
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Superclass:	Multicrustacea
Class:	Tantulocarida G. A. Boxshall & R. J. Lincoln, 1983 [1]
Families
Basipodellidae Cumoniscidae (formerly Deoterthridae) Doryphallophoridae Microdajidae Onceroxenidae

Description

In the Tantulocarida, animals do not ever present eyes.^[4]

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.^[5] 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.^[6]

Body length

Members of this subclass are minute – less than 0.3 millimetres (0.012 in) in length and have a dramatic reduction in body form compared to other crustaceans, with an unsegmented, sac-like thorax and a much reduced abdomen.^[7] One tantulocarid species, Tantulacus dieteri, is the world's smallest arthropod, with a total body length of only 85 micrometres (0.0033 in).^[8]

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 instars. 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 female, or a fully developed free-living, non-feeding and sexually-reproducing male or female.^{[9][10][11][12][13]} 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.^[14]

Classification

Five families are recognised:^[15]

Basipodellidae Boxshall & Lincoln, 1983:[16] 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:[17] Doryphallophora Huys, 1990 Paradoryphallophora Ohtsuka & Boxshall, 1998 Microdajidae Boxshall & Lincoln, 1987:[18] Microdajus Greve, 1965 Xenalytus Huys, 1991

Cumoniscidae Nierstrasz & Brender à Brandis, 1923 (formerly family Deoterthridae:[19] 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:[20] Onceroxenus Boxshall & Lincoln, 1987