''Limnopilos naiyanetri'', commonly referred to as the Thai micro crab or pill-box crab, is a freshwater hymenosomatid crab endemic to

Thailand Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. With a population of almost 66 million, it spa ...

. Its presence has only been confirmed in the

Tha Chin River The Tha Chin River (, , ) is a distributary of the Chao Phraya River, in Thailand. It splits in the province of Chai Nat and then flows west from the Chao Phraya through the central plains, until it empties into the Gulf of Thailand in Samut S ...

. The species was described in 1991 and represents the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

of ''Limnopilos''. The Thai micro crab was first introduced to the aquarium hobby in 2008 when it was imported to Germany by the tropical fish importer Aquarium Glaser GmbH, and has slowly grown in popularity with aquarium hobbyists. It remains a relatively rare species on the market and detailed information on the husbandry of this species is scarce.

Description

This species is quite small, the carapace reaching only 1 cm in width at maturity. The leg span may reach lengths of 2.5 cm. Individuals of this species are semi-translucent and range from grey to light brown. It has a circular, flat

carapace A carapace is a 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 tortoises, the unde ...

with contiguous gastro-cardiac grooves and margin. A defining feature of this species is a setose or pilose carapace and chelipeds. These soft hairs collect detritus, which may provide food or serve as camouflage for the animal. Like other hymenosomatids'', Limnopilos naiyanetri'' has a weak or absent

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...

. There are many characteristics which distinguish it from other hymenosomatid crabs, however: its

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 ...

is not distinctly trilobate, the eyes are not concealed from dorsal view by the anterior carapace, and male first

pleopods The anatomy of a decapod consists of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment – often called a somite – may possess one pair of appendages, although in various groups these ma ...

have a simple structure. In both male and female individuals, all abdominal segments are free and unfused. Many aspects of this species' ecology and natural history are still poorly understood, and there have been no documented instances of reproduction in captivity. The crabs release free-moving larvae which are assumed to develop in freshwater, but this is unconfirmed.

Distribution and habitat

''Limnopilos naiyanetri'' is endemic to Thailand. The first identified individuals were collected from a section of the

in the Nakhom Pathom province, where they were found on the roots of water hyacinths. The species is elusive and its presence has not been confirmed outside of this river basin. They are nocturnally active and forage for detritus on aquatic plants and mosses, although they may act as opportunistic carnivores. In aquariums, this species should be kept between pH 6.5 and 7.3 with temperatures between 21°C (70°F) and 27°C (82 °F). These crabs are sensitive to water conditions and nutrient levels in the water should be closely monitored.

Taxonomic history

''Limnopilos naiyanetri'' was described in 1991 by Christina Chuang and Peter Ng, but shortly thereafter in 1995 Ng reclassified the species under the genus ''Hymenicoides'', a closely related group of hymenosomatids. In 1996, Ng and Chuang commented that the characteristics which made them decide the crab represented a new genus than ''Hymenicoides'' originally were the lack of a protuberance on the outer surface of the male cheliped and structural differences of the telson, but after reconsideration these seemed to be interspecific rather than intergeneric differences. However, Danièle Guinot and Bertrand Richer de Forges studied specimens in 1997 and commented that the crabs may in fact represent a genus separate from ''Hymenicoides''. The genus ''Limnopilos'' and the species ''Limnopilos naiyanetri'' were confirmed in 2007, along with two new species of ''Limnopilos'', by Tohru Naruse and Peter Ng.

References

{{Taxonbar, from=Q13764808 Crabs Freshwater crustaceans of Asia Crustaceans of Thailand Endemic fauna of Thailand Crustaceans described in 1991 Taxa named by Peter Kee Lin Ng