''Argulus ambystoma'' is a species of

branchiura The family Argulidae, whose members are commonly known as carp lice or fish lice, are parasitic crustaceans in the class Ichthyostraca. It is the only family in the monotypic subclass Branchiura and the order Arguloida, although a second family, ...

n parasitic on

Lake Patzcuaro salamander The Lake Patzcuaro salamander, locally known as achoque, ''Ambystoma dumerilii'', is a neotenic salamander species. This salamander is found in Lake Pátzcuaro, a high-altitude lake in the Mexican state of Michoacán. This is located in the Mesa ...

s, sharing that species' very limited range in

Lago de Pátzcuaro __NOTOC__ Lago, which means "lake" in Italian, Portuguese, Spanish and Galician, may refer to: Places *Lago, Calabria, a ''comune'' in the Province of Cosenza, Italy *Lago, Mexico, a municipality zone in the State of Mexico *Lago District, a ''dis ...

, Mexico. The male has a total length of 3–4 mm with 2 dark triangular marks on the dorsal surface of the

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

and large dark patches marking the location of the

testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoster ...

. The larger (4–6 mm) female is generally mottled without large dark areas. It lives among the external

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

s of its

neotenous Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the physiological, or somatic, development of an organism, typically an animal. Neoteny is found in modern humans compa ...

host, only occasionally straying from this hiding place during darkness. This retiring nature may explain why this animal remained undiscovered until recently.

References

* Freshwater crustaceans of North America Endemic crustaceans of Mexico Crustaceans described in 2003 {{Crustacean-stub