Tantulocarida

Tantulocarida is a highly specialised group of parasitic crustaceans that consists of about 33 species, treated as a subclass of the class Hexanauplia (which also includes copepods and barnacles). They are typically ectoparasites that infest copepods, isopods, tanaids, amphipods and ostracods.

Body length
Members of this subclass are minute – less than 0.3 mm 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. One tantulocarid species, Tantulacus dieteri, is the world's smallest arthropod, with a total body length of only 85 um.

Life cycle
The tantulocarid life cycle is unique. It does not follow the usual moulting cycle of all crustaceans; instead, the mature adult actually develops within an attached parasitic tantulus larva.

Classification
Five families 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

Deoterthridae Boxshall & Lincoln, 1987 : Onceroxenidae Huys, 1991 :
 * 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
 * Onceroxenus Boxshall & Lincoln, 1987