''Austrothelphusa transversa'' ''( von Martens, 1868)'', also known as the inland crab, freshwater crab, or tropical freshwater crab is a species of freshwater crab

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 else ...

to Australia. ''A. transversa'' is the most widely-dispersed species of its genus, as it has

adaptations In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the ...

giving it a high tolerance to drought and arid conditions.

Taxonomy and Description

The inland crab has undergone numerous changes of specific name, changing genera, subgenera, and subfamilies, including ''Parathephusa'', ''Liotelphusa'', and ''Holthuisana''. Due to the loss of type specimens, similarities between certain genera, and most recently molecular testing, the species is currently grouped with six other species in the genus ''Austrothelphusa''. The coloration of the inland crab varies among individuals; most have a brown, maroon, and grey coloring to the exoskeleton, or a similar shade. The inland crab has a relatively smooth carapace which grows to around in diameter. Like other

decapods The Decapoda or decapods (literally "ten-footed") are an order (biology), order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, Caridea, shrimp and Dendrobranchiata, prawns. Most ...

, the inland crab has one pair of claws, one of which is longer than the other, four pairs of legs, and a relatively round carapace.

Distribution and Habitat

The inland crab is endemic to the Australian mainland and is widely distributed throughout the north-western half of the continent, living both in the arid inland conditions of central Australia as well as the tropical and sub-tropical rivers of northern Australia. The inland crab is predominantly found throughout

ephemeral Ephemerality (from the Greek word , meaning 'lasting only one day') is the concept of things being transitory, existing only briefly. Academically, the term ephemeral constitutionally describes a diverse assortment of things and experiences, fr ...

rivers, creeks, and waterholes throughout Queensland (QLD) and the Northern Territory (NT), whilst located in pockets in the north-eastern parts of Western Australia (WA) and South Australia (SA), and parts of north-western New South Wales (NSW).

Behaviour

Aestivation

The inland crab is thought to estivate into the deep burrows in which the crab builds in clay or sediment banks as a way of dealing with prolonged droughts, waiting for the rain to restore the creeks, rivers, and water holes, allowing them to exit æstivation. The

burrowing An Eastern chipmunk at the entrance of its burrow A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of locomotion. Burrows provide a form of s ...

habit of the crab is vital for its survival, as it allows individuals to find a moist substrate, close to the water table, in which the animal æstivates during dry periods, similarly to the

common yabby The common yabby (''Cherax destructor'') is an Australian freshwater crustacean in the Parastacidae family. It is listed as a vulnerable species of crayfish by the International Union for Conservation of Nature (IUCN), though wild yabby popula ...

. The crab burrows average some in depth, and the entrance to the tunnel contains a plug, creating a chamber in which moisture remains trapped, preventing the crab from drying out. This prolongs the time the crab can remain in its burrow.

Diet

The return of water to ephemeral rivers in the wet season supports a temporary abundance of aquatic life, such as algae and

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...

. Though the inland crab is an omnivore, they feed primarily on algae that bloom when the water returns. However, the inland crab is an opportunistic scavenger, and will feed on any decaying animal matter it encounters.

Amphibious

The inland crab's modified gills work as lungs when exposed to the atmosphere, allowing the animals to become amphibious. This is a common trait among other crustacean species. This adaptation allows the inland crab to leave the water, helping it thermoregulate, as small pools of water can fluctuate widely in temperature and oxygenation throughout the day. If conditions become intolerable, the crab can leave the water and seek shelter among roots, leaf litter, and other

debris Debris (, ) is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, as in geology, large rock fragments left by a melting glacier, etc. Depending on context, ''debris'' can refer to ...

Reproduction

The female crab carries fertilized eggs under her

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the to ...

, which is tucked under the crab's

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...

. Females can lay anything from 100 to 350 eggs. The female holds on to her eggs and young throughout larval development, until the early juvenile stage. Then, the mother will disperse the young into the close surroundings, where they will fend for themselves. The mother crab is believed to hold onto her young during the æstivation period in the burrows, releasing the young crabs when she exits æstivation. This means that the young are protected through the most difficult part of the year, giving the young an optimal chance for success as the waterways refill.

Conservation Actions

Although considered to be of 'Least Concern' by the IUCN, the inland crab occurs in several protected areas, including

Sturt National Park The Sturt National Park is a protected national park that is located in the arid far north-western corner of New South Wales, in eastern Australia. The national park is situated approximately northwest of Sydney and the nearest town is , awa ...

. Due to its wide distribution, the inland crab is seen as of 'Least Concern', but to what extent the species will remain at this level will depend on further studies. More recent studies predict that due to its wide distribution, it could be more speciose than originally estimated.

Threats

Urbanization Urbanization (or urbanisation) refers to the population shift from rural to urban areas, the corresponding decrease in the proportion of people living in rural areas, and the ways in which societies adapt to this change. It is predominantly t ...

and human modification to natural rivers are among the factors threatening the inland crab. Altering the natural flow of creeks, modifying the structure of their banks, especially replacing natural substrate with concrete channels, has a direct impact on the species' ability to burrow and æstivate. Along with prolonged drought,

agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people t ...

, and

climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

, the inland crab will have to face even longer periods without water.

References

{{Taxonbar, from=Q13431741 Gecarcinucoidea Freshwater crustaceans of Australia