''Platythelphusa'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

freshwater crab Around 1,300 species of freshwater crabs are distributed throughout the tropics and subtropics, divided among eight families. They show direct development and maternal care of a small number of offspring, in contrast to marine crabs, which rele ...

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found els ...

Lake Tanganyika Lake Tanganyika () is an African Great Lake. It is the second-oldest freshwater lake in the world, the second-largest by volume, and the second-deepest, in all cases after Lake Baikal in Siberia. It is the world's longest freshwater lake. T ...

. It has been placed in a number of families, including a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

, Platythelphusidae, as well as

Potamidae Potamidae is a family of freshwater crabs. It includes more than 650 species and nearly 100 genera, which are placed into two subfamilies: Potaminae and Potamiscinae. Subfamily Potaminae The Potaminae Ortmann, 1896 are distributed around the Me ...

and its current position in the

Potamonautidae Potamonautidae is a family of freshwater crabs endemic to Africa, including the islands of Madagascar, the Seychelles, Zanzibar, Mafia, Pemba, Bioko, São Tomé, Príncipe and Sherbro Island. It comprises 18 extant genera and 138 extant species. ...

, and has also been treated as a

subgenus In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed betw ...

of ''

Potamonautes ''Potamonautes'' is a genus of African freshwater crabs in the family Potamonautidae. It is both the most widespread and most diverse genus of African freshwater crabs, including more than half the species of this continent.Yeo, C.J.; Klaus, S.; ...

''. It forms a

monophyletic group A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

, possibly nested within the genus ''Potamonautes'', which would therefore be

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

. The genus is the only

evolutionary radiation An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. Radiations may affect one clade or many, and be rap ...

of crabs to have occurred in a freshwater

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much lar ...

, and it occurred recently, probably since the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58 This parallels the better known radiation of cichlid fishes in Lake Tanganyika. Only one other species of freshwater crab is found in Lake Tanganyika, '' Potamonautes platynotus''.

Taxonomic history

The first freshwater crab to be described from Lake Tanganyika, by

Alphonse Milne-Edwards Alphonse Milne-Edwards (Paris, 13 October 1835 – Paris, 21 April 1900) was a French mammalogist, ornithologist, and carcinologist. He was English in origin, the son of Henri Milne-Edwards and grandson of Bryan Edwards, a Jamaican planter who se ...

in 1887, was considered so distinct from the other crabs known up to that time that it was placed in a new genus, as ''Platythelphusa armata''. Twelve years later, a second species was described by W. A. Cunnington, leader of the third Tanganyika Expedition, and was also placed in a separate genus, as ''Limnothelphusa maculata''. The same author later described a third species, ''Platythelphusa conculata'', and eventually realised that all three belonged to the same genus, reducing ''Limnothelphusa'' to a

taxonomic synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...

. In 1952, Capart did not recognise the species ''P. conculcata'', but added four new species, ''P. denticulata'', ''P. echinata'', ''P. polita'' and ''P. tuberculata''. Since that time, ''P. conculcata'' has been restored, and two new species have been described, ''P. immaculata'' and ''P. praelongata''.

Distribution

All nine species live in relatively shallow waters around the edge of Lake Tanganyika. While four countries border Lake Tanganyika (

Burundi Burundi (, ), officially the Republic of Burundi ( rn, Repuburika y’Uburundi ; Swahili: ''Jamuhuri ya Burundi''; French: ''République du Burundi'' ), is a landlocked country in the Great Rift Valley at the junction between the African Gr ...

Democratic Republic of the Congo The Democratic Republic of the Congo (french: République démocratique du Congo (RDC), colloquially "La RDC" ), informally Congo-Kinshasa, DR Congo, the DRC, the DROC, or the Congo, and formerly and also colloquially Zaire, is a country in ...

Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...

and

Zambia Zambia (), officially the Republic of Zambia, is a landlocked country at the crossroads of Central, Southern and East Africa, although it is typically referred to as being in Southern Africa at its most central point. Its neighbours are ...

), only two species have been found in all four countries, ''P. armata'' and ''P. conculcata''. One species, ''P. polita'', has been found in all except Zambia; two (''P. echinata'' and ''P. tuberculata'') have been found in Burundi and Tanzania; one has been found in Tanzania and Zambia (''P. maculata''); one is only known from Zambia (''P. praelongata'') and two have only been seen in Tanzania (''P. denticulata'' and ''P. immaculata''). However, many of the species are poorly known, and their true distributions may be wider than is currently known.

Species

''Platythelphusa armata''

As the largest species in the genus (up to in carapace width), ''Platythelphusa armata'' is subject to small-scale

fishery Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life; or more commonly, the site where such enterprise takes place (a.k.a. fishing ground). Commercial fisheries include wild fisheries and fish farms, ...

. Adults live at depths of , while juveniles live at depths of , and often inhabit discarded '' Neothauma tanganyicense'' shells. The species is listed as

Least Concern A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. Th ...

by the IUCN.

''Platythelphusa conculcata''

''Platythelphusa conculcata'' is found at depths of , and is listed as Least Concern by the IUCN.

''Platythelphusa denticulata''

''Platythelphusa denticulata'' is known from few sites, all in Tanzania. Though it may have a low population, there is no evidence of a decline and it is listed as Least Concern by the IUCN.

''Platythelphusa echinata''

''Platythelphusa echinata'' is found at depths of on the Tanzanian and Burundian shores of Lake Tanganyika. It lives where the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

is rocky or sandy, and occasionally uses old ''

Neothauma ''Neothauma '' is a genus of freshwater snail with a gill and an operculum, an aquatic gastropod mollusc in the subfamily Bellamyinae of the family Viviparidae. MolluscaBase eds. (2021). MolluscaBase. Neothauma E. A. Smith, 1880. Accesse ...

'' shells.

''Platythelphusa immaculata''

''Platythelphusa immaculata'' is known from only 25 specimens, but is listed as Least Concern, because there are no apparent threats to its survival.

''Platythelphusa maculata''

''Platythelphusa maculata'' lives on sand and rocks, and occasionally in ''Neothauma'' shells, at depths of , and is listed as Least Concern.

''Platythelphusa polita''

''Platythelphusa polita'' lives on sand and rocks, and occasionally in ''Neothauma'' shells, at depths of , and is listed as Least Concern.

''Platythelphusa praelongata''

''Platythelphusa praelongata'' lives at the greatest depth of any ''Platythelphusa'' species, the single known specimen having been collected at , around

Mbita Island Mbita Point is a town in the former province of Nyanza, Kenya, currently in Homa Bay County, on the shores of Lake Victoria. It is home to the Thomas Odhiambo campus of the International Centre of Insect Physiology and Ecology (ICIPE). A public p ...

, and is listed as

Data Deficient A data deficient (DD) species is one which has been categorized by the International Union for Conservation of Nature (IUCN) as offering insufficient information for a proper assessment of conservation status to be made. This does not necessarily ...

''Platythelphusa tuberculata''

''Platythelphusa tuberculata'' has longer legs than the other species, and lives at the northern end of Lake Tanganyika, on muddy substrates. It has been found in the

stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

s of fish including '' Chrysichthys brachynema'' and ''

Bathybagrus stappersii ''Bathybagrus stappersii'' is a species of fish endemic to Lake Tanganyika on the border of Burundi, the Democratic Republic of the Congo, Tanzania, and Zambia. It grows to a length of 45.0 cm (17.7 inches) SL and is a component of local su ...

'' (formerly ''Chrysichthys stappersii'').

References

{{Taxonbar, from=Q2594196 Potamoidea Freshwater crustaceans of Africa Fauna of Lake Tanganyika Taxonomy articles created by Polbot