''Perisesarma guttatum'', the red-claw mangrove crab, is a

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

species in the genus '' Perisesarma'' and the family

Sesarmidae The Sesarmidae are a family of crabs, previously included in the Grapsidae by many authors. Several species, namely in '' Geosesarma'', '' Metopaulias'', and '' Sesarma'', are true terrestrial crabs. They do not need to return to the sea even fo ...

. It is distributed in coastal

brackish water Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuary ...

habitats of the western

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...

Description

Along with the other species within the genus '' Perisesarma'', the red-claw mangrove crab has a relatively square-shaped

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 ...

and a “tooth” protruding off the sides of it. The claw of the crab consists of a palm and

dactylus The dactylus is the tip region of the tentacular club of cephalopods and of the leg of some crustaceans (see arthropod leg). In cephalopods, the dactylus is narrow and often characterized by the asymmetrical placement of suckers (i.e., the vent ...

. At the end of the dactylus are oval or circular shaped bumps called

tubercles In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projection, b ...

. The part leading up to the claws, the chelar carpus, also has pectinate crests on males within the genus. A pectinate crest is a ridge-like projection on the crab; these ridges line the chelar carpus side-by-side. Different species of ''Perisesarma'' vary in the amount of their tubercles in addition to the number of pectinate crests. ''P. guttatum'' have 20 pectinate crests and 11 to 13 oval-shaped tubercles on top of their claws. Their claws are reddish in color with bright orange internal palms. The carapace is about 3 cm in length and between 1.5 and 2.2 cm in width on average in adults. At maturity, males display larger claws than females, showing

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

. ''P. samawati'', a sympatric species, was confused for ''P. guttatum'' until more recently, though their morphologies are distinctly different. Unlike ''P. guttatum'', ''P. Samawati'' only has 7 to 9 tubercles on the upper surface of their claws. The sizes of their bodies differs as well.

Distribution

''P. guttatum'' are mangrove inhabitants mostly located by ''

Avicennia marina ''Avicennia marina'', commonly known as grey mangrove or white mangrove, is a species of mangrove tree classified in the plant family Acanthaceae (formerly in the Verbenaceae or Avicenniaceae). As with other mangroves, it occurs in the intert ...

''. The species inhabit these mangroves in east African coasts and

Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...

. Despite increases in pollution from sewage in these areas, the crabs tolerate and are even capable of using the excess nutrients, making them less helpful in measuring mangrove health.

Ecology

The species use burrows and natural crevices made by ''

Neosarmatium smithi ''Neosarmatium smithi'', is a swimming crab species in the genus '' Neosarmatium''. Distributed all over marine and brackish waters of Indo-West Pacific regions. Distribution A mangrove inhabitant, it is found all over South Africa, Madagascar, ...

'' to hide from predators and also for survival. ''P. guttatum'' are mainly

herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...

, eating dead plant material and other

organic matter Organic matter, organic material or natural organic matter is the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come fro ...

foraged from the

estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

forest floor The forest floor, also called detritus or wikt:duff#Noun 2, duff, is the part of a forest ecosystem that mediates between the living, aboveground portion of the forest and the mineral soil, principally composed of dead and decaying plant matter ...

during low

tides Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

. Their diets therefore contribute to leaf turnover and the general removal of matter from the

substratum Substrata, plural of substratum, may refer to: *Earth's substrata, the geologic layering of the Earth *''Hypokeimenon'', sometimes translated as ''substratum'', a concept in metaphysics *Substrata (album), a 1997 ambient music album by Biosphere * ...

Reproduction and life history

Females begin to reach

sexual maturity Sexual maturity is the capability of an organism to reproduce. In humans, it is related to both puberty and adulthood. ''Puberty'' is the biological process of sexual maturation, while ''adulthood'', the condition of being socially recognized ...

around 2 years old; adults then mate throughout the year, but a study suggests that breeding correlates with

lunar phases A lunar phase or Moon phase is the apparent shape of the Moon's directly sunlit portion as viewed from the Earth. Because the Moon is Tidal locking, tidally locked with the Earth, the same Hemisphere (geometry), hemisphere is always facing the ...

. Females tend to release their

larvae A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...

before spring tides, which occur during new and full moons. However, females cannot breed for two consecutive spring tides, which suggests this pattern is seen due to two breeding groups within one population. During the early stages of life, planktonic larvae move offshore and are distributed with the help of

ocean currents An ocean current is a continuous, directed movement of seawater generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours ...

. They later return as megalopa larvae – the step in their development that comes after 5 planktonic life stages – and settle in the nearshore environments around where they were once born.

References

{{Portal bar, Crustaceans Sesarmidae Crustaceans described in 1869