''Johora singaporensis'', the ''Singapore stream crab'' or ''Singapore freshwater crab'', is a critically endangered species of

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 relea ...

endemic to Singapore. It grows to a size of wide.

Ecology

''J. singaporensis'' lives in

stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a stream ...

s running through undisturbed forest, where it hides under rocks at the stream's edge, or inside aggregations of leaves and

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

. It is mostly

nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

, feeding on detritus and oligochaete worms which live in the muddy stream bed.

Distribution

''J. singaporensis'' only lives in Singapore, and has only ever been recorded from two locations. One of these was inside Bukit Timah Nature Reserve, but that population is believed to have been extirpated, as recent surveys have failed to find any examples there. The second population is outside the nature reserve at

Bukit Batok Bukit Batok, often abbreviated as Bt Batok, is a planning area and matured residential town located along the eastern boundary of the West Region of Singapore. Bukit Batok statistically ranks in as the 25th largest, the 12th most populous and ...

, partly on private land, and partly on military land.

Acidification Acidification may refer to: * Ocean acidification, decrease in the pH of the Earth's oceans * Freshwater acidification, atmospheric depositions and soil leaching of SOx and NOx * Soil acidification, buildup of hydrogen cations, which reduces the ...

of the first stream may have caused the first population to die out, while a lowering of the water table in the second stream threatens the second population. ''J. singaporensis'' is one of three freshwater crabs that are endemic to Singapore. The others are '' Irmengardia johnsoni'', and the critically endangered '' Parathelphusa reticulata''.

Phylogeny

The relatives of ''J. singaporensis'' in the genus ''

Johora ''Johora'' is a genus of freshwater crabs found in the Malay Peninsula and surrounding islands. It includes the following species: *'' Johora aipooae'' (Ng, 1986) *'' Johora counsilmani'' (Ng, 1985) *'' Johora gapensis'' (Bott, 1966) *'' Johora ...

'' are found across the Straits of Johor on the adjacent

Malay Peninsula The Malay Peninsula (Malay: ''Semenanjung Tanah Melayu'') is a peninsula in Mainland Southeast Asia. The landmass runs approximately north–south, and at its terminus, it is the southernmost point of the Asian continental mainland. The area ...

and some offshore islands, making ''J. singaporensis'' the southernmost species in the genus. It probably forms the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

to a

clade 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, ...

comprising '' J. tiomanensis'', '' J. counsilmani'', '' J. murphyi'', '' J. johorensis'', '' J. gapensis'' and '' J. intermedia'', from which it separated about 5 million years ago, at a time when the eustatic changes in global sea level may have opened up a land bridge to Singapore.

Status

''Johora singaporensis'' is listed by the International Union for Conservation of Nature as Critically Endangered under criteria B1ab(iii)+2ab(iii), which refer to the small size of the remaining populations and the ongoing deterioration of the habitat. The species' restriction to a single small island is likely to have increased the threat of extinction. In 2012, it was included among the world's 100 most threatened species, in a report by the IUCN Species Survival Commission and the Zoological Society of London.

References

External links

* {{Taxonbar, from=Q774691 Potamoidea Freshwater crustaceans of Asia Arthropods of Singapore Crustaceans described in 1986