Platythelphusa
Encyclopedia
Platythelphusa is a genus
of freshwater crab
s endemic to Lake Tanganyika
. It has been placed in a number of families, including a monotypic
family
, Platythelphusidae, as well as Potamidae
and its current position in the Potamonautidae
, and has also been treated as a subgenus
of Potamonautes
. It forms a monophyletic group, possibly nested within the genus Potamonautes, which would therefore be paraphyletic
. The genus is the only evolutionary radiation
of crab
s to have occurred in a freshwater lake
, and it occurred recently, probably since the Pliocene
. 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
.
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.
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.
, Democratic Republic of the Congo
, Tanzania
and Zambia
), 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.
. Adults lives at depths of 5–30 m (16.4–98.4 ), while juveniles
live at depths of 1–10 m (3.3–32.8 ft), and often inhabit discarded Neothauma tanganyicense
shells. The species is listed as Least Concern
by the IUCN.
, is lsted as Least Concern by the IUCN.
is rocky or sandy, and occasionally uses old Neothauma
shells
.
.
s of fish including Chrysichthyes brachynema and Chrysichthyes stappersi.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of freshwater crab
Freshwater crab
There are around 1,300 species of freshwater crabs, 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 release thousands of planktonic larvae. This limits...
s endemic to Lake Tanganyika
Lake Tanganyika
Lake Tanganyika is an African Great Lake. It is estimated to be the second largest freshwater lake in the world by volume, and the second deepest, after Lake Baikal in Siberia; it is also the world's longest freshwater lake...
. It has been placed in a number of families, including a monotypic
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
family
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...
, Platythelphusidae, as well as Potamidae
Potamidae
Potamidae is a family of freshwater crabs. Its more than 650 species and nearly 100 genera are divided into two subfamilies — Potaminae around the Mediterranean Sea, on Socotra and eastwards to Northern India, and Potamiscinae in East Asia....
and its current position in the Potamonautidae
Potamonautidae
Potamonautidae is a family of freshwater crabs endemic to tropical parts of Africa and adjacent islands, including 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
Subgenus
In biology, a subgenus is a taxonomic rank directly below genus.In zoology, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the generic name and the specific epithet: e.g. the Tiger Cowry of the Indo-Pacific, Cypraea tigris Linnaeus, which...
of Potamonautes
Potamonautes
Potamonautes is a genus of freshwater crabs in the family Potamonautidae. It contains the following species:*Potamonautes adeleae Bott, 1968*Potamonautes alluaudi *Potamonautes aloysiisabaudiae...
. It forms a monophyletic group, possibly nested within the genus Potamonautes, which would therefore be paraphyletic
Paraphyly
A group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
. The genus is the only evolutionary radiation
Evolutionary radiation
An evolutionary radiation is an increase in taxonomic diversity or morphological disparity, due to adaptive change or the opening of ecospace. Radiations may affect one clade or many, and be rapid or gradual; where they are rapid, and driven by a single lineage's adaptation to their environment,...
of crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s to have occurred in a freshwater lake
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
, and it occurred recently, probably since the Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
. This parallels the better known radiation of cichlid fishes
Cichlid
Cichlids are fishes from the family Cichlidae in the order Perciformes. Cichlids are members of a group known as the Labroidei along with the wrasses , damselfish , and surfperches . This family is both large and diverse. At least 1,300 species have been scientifically described, making it one of...
in Lake Tanganyika. Only one other species of freshwater crab is found in Lake Tanganyika, Potamonautes platynotus
Potamonautes platynotus
Potamonautes platynotus is a species of freshwater crab which is endemic to Lake Tanganyika, where it is the only freshwater crab outside the genus Platythelphusa. Although primarily aquatic, P. platynotus is sometimes seen out of water, and can survive for many hours without water....
.
Taxonomic history
The first freshwater crab to be described from Lake Tanganyika, by Alphonse Milne-EdwardsAlphonse Milne-Edwards
Alphonse Milne-Edwards was a French mammalologist, ornithologist and carcinologist. He was English in origin, the son of Henri Milne-Edwards and grandson of Bryan Edwards, a Jamaican planter who settled at Bruges .Milne-Edwards obtained a medical degree in 1859 and became assistant to his father...
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.
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 (BurundiBurundi
Burundi , officially the Republic of Burundi , is a landlocked country in the Great Lakes region of Eastern Africa bordered by Rwanda to the north, Tanzania to the east and south, and the Democratic Republic of the Congo to the west. Its capital is Bujumbura...
, Democratic Republic of the Congo
Democratic Republic of the Congo
The Democratic Republic of the Congo is a state located in Central Africa. It is the second largest country in Africa by area and the eleventh largest in the world...
, Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
and Zambia
Zambia
Zambia , officially the Republic of Zambia, is a landlocked country in Southern Africa. The neighbouring countries are the Democratic Republic of the Congo to the north, Tanzania to the north-east, Malawi to the east, Mozambique, Zimbabwe, Botswana and Namibia to the south, and Angola to the west....
), 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, Platythelphusa armata is subject to small-scale fisheryCrab fisheries
Crab fisheries are fisheries which capture or farm crabs. True crabs make up 20% of all crustaceans caught and farmed worldwide, with about 1.4 million tonnes being consumed annually. The horse crab, Portunus trituberculatus accounts for one quarter of that total...
. Adults lives at depths of 5–30 m (16.4–98.4 ), while juveniles
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
live at depths of 1–10 m (3.3–32.8 ft), and often inhabit discarded Neothauma tanganyicense
Neothauma tanganyicense
Neothauma tanganyicense is a species of freshwater snail with a gill and an operculum, an aquatic gastropod mollusc in the family Viviparidae.This is the only species in the genus Neothauma.- Distribution :...
shells. The species is listed as Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
by the IUCN.
Platythelphusa conculcata
Platythelphusa conculcata is found at depths of 20–60 m (65.6–196.9 ), and is listed as Least Concern by the IUCN.Platythelphusa denticulata
Platythelphusa denticulata is known from few sites, all in Tanzania, but because of the low levels of disturbance and pollutionPollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...
, is lsted as Least Concern by the IUCN.
Platythelphusa echinata
Platythelphusa echinata is found at depths of 5–30 m (16.4–98.4 ) on the Tanzanian and Burundian shores of Lake Tanganyika. It lives where the substrateSubstrate (biology)
In biology a substrate is the surface a plant or animal lives upon and grows on. A substrate can include biotic or abiotic materials and animals. For example, encrusting algae that lives on a rock can be substrate for another animal that lives on top of the algae. See also substrate .-External...
is rocky or sandy, and occasionally uses old Neothauma
Neothauma
Neothauma tanganyicense is a species of freshwater snail with a gill and an operculum, an aquatic gastropod mollusc in the family Viviparidae.This is the only species in the genus Neothauma.- Distribution :...
shells
Gastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
.
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 1–60 m (3.3–196.9 ft), and is listed as Least Concern.Platythelphusa polita
Platythelphusa polita lives on sand and rocks, and occasionally in Neothauma shells, at depths of 5–60 m (16.4–196.9 ), 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 40–80 m (131.2–262.5 ), around Mbita Island, and is listed as Data DeficientData Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
.
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 stomachStomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
s of fish including Chrysichthyes brachynema and Chrysichthyes stappersi.