Tantulocarida is a highly specialised group of parasitic 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 that consists of about 33 species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

, treated as a subclass of the class

Class (biology)

In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

 Maxillopoda

Maxillopoda

Maxillopoda is a diverse class of crustaceans including barnacles, copepods and a number of related animals. It does not appear to be a monophyletic group, and no single character unites all the members.-Description:...

 (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,...

s and 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). They are typically ectoparasites that infest 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,...

s, isopods, tanaids

Tanaidacea

The crustacean order Tanaidacea make up a minor group within the class Malacostraca. There are about 940 species in this order.-Description:...

, amphipods and ostracod

Ostracod

Ostracoda is a class of the Crustacea, sometimes known as the seed shrimp because of their appearance. Some 65,000 species have been identified, grouped into several orders....

s. Members of this subclass are minute — less than 0.3 millimetre (0.0118110236220472 in) in length and have a dramatic reduction in body form compared to other 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, with an unsegmented sac-like thorax

Thorax

The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...

 and a much reduced abdomen

Abdomen

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...

. One tantulocarid species, Tantulacus dieteri, is the world's smallest arthropod, with a total body length of only 85 um.

Classification

Four families

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 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
  Stygotantulus
  Stygotantulus stocki is a species of crustacean, living as an ectoparasite on harpacticoid copepods of the families Tisbidae and Canuellidae. It is the smallest arthropod in the world, at a length of less than . The specific epithet stocki commemorates Jan Hendrik Stock, a Dutch carcinologist....
  
  Boxshall & Huys, 1989

Doryphallophoridae Huys, 1991:

• Doryphallophora Huys, 1990
• Paradoryphallophora Ohtsuka & Boxshall, 1998

Microdajidae Boxshall & Lincoln, 1987:

• Microdajus Greve, 1965
• Xenalytus Huys, 1991

Deoterthridae Boxshall & Lincoln, 1987:

• 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
• Onceroxenus Boxshall & Lincoln, 1987
• Tantulacus Huys, Andersen & Kristensen, 1992