Decapoda, Potamonautidae

Wed Jan 14, 2015 4:59 pm

Family Potamonautidae
The Potamonautidae are a family of freshwater crabs endemic to tropical parts of Africa and adjacent islands. Freshwater crabs are widely distributed in South Africa where they can be found in a variety of aquatic habitats ranging from rivers, streams, and lakes to swamp forests. While some species have specific habitat requirements restricting their range, other species are able to tolerate a wide range of habitat types.
The southern African region is home to nineteen species of freshwater crabs all belonging to the genus Potamonautes. These crabs show high levels of species endemism (84%) to the southern African region and to the country of South Africa (74%).
Carapace outlines and markings on top of the carapace, dentition patterns and maximum width of the carapace and distribution range are distinguishing features between species.

Freshwater crabs lack larval stages; however, they produce a large number of juveniles (more than 850 eggs per female were recorded in Potamonautes sidneyi). The adults are thought to be amphibious, with a relatively high dispersal capacity, and are frequently seen on foraging excursions on land.

Links: A conservation assessment of the freshwater crabs of southern Africa (Brachyura: Potamonautidae). Neil Cumberlidge and Savel R. Daniels

Re: Africa Wild Crustaceans Book (Subphylum Crustacea)

Wed Jan 14, 2015 5:00 pm

Single-spined River Crab Potamonautes unispinus
Subphylum Crustacea. Suborder Brachyra. Order Decapoda. Family Potamonautidae. Subfamily Potamonautinae

Image © BluTuna
Rondebult Bird Sanctuary, Gauteng

A large bodied riverine crab. It always possesses a single, well-deŽfined epibranchial tooth at the epibranchial corner of the carapace. It is characterized by a smooth to granulated anteriolateral margin.
Potamonautes unispinus is heterochelous, with right handedness in both sexes being dominant.
Told from P. warrenii by the lack of strongly denticulate anterolateral margins of the carpace.

South Africa and Zimbabwe. This species is found in the highveld (temperate) region from the interior plateau of Zimbabwe to the South African Provinces of Mpumalanga, Limpopo, Gauteng, North West, and Free State. This species has not been recorded from KwaZulu-Natal, Eastern Cape, Western Cape, and Northern Cape Provinces.


Links: The Status and Distribution of Freshwater Biodiversity in Southern Africa. Will Darwall, D. Tweddle, K. Smith, P. Skelton

Re: Africa Wild Crustaceans Book (Subphylum Crustacea)

Wed Jan 14, 2015 11:37 pm

Burrowing Feshwater Crab Potamonautes calcaratus
Subphylum Crustacea. Suborder Brachyra. Order Decapoda. Family Potamonautidae. Subfamily Potamonautinae

Image © flying cheetah
Pretoriuskop area, Kruger National Park

The adult size range is from cws 35–42 mm. It has a smooth rounded carapace.
Carapace medium height; epibranchial tooth large forming deep epibranchial sinus, positioned well behind postfrontal crest; carapace sidewall in three parts; anterolateral margin behind epibranchial tooth raised, smooth, curving inward over carapace at posterior end, not continuous with posterolateral margin; large, pointed distal tooth on both anterior-inferior and posterior-inferior margins of merus of cheliped; dactylus of major cheliped of adult male flat, broad, enclosing narrow interspace; chelipeds highly unequal.

The geographic range of this species includes Mpumalanga and North-West Provinces in South Africa, and Mozambique. It is also found in the Charre and Caia River basins in the lower Zambezi River basin in Zimbabwe.

The habitat of this species is seasonal marshy wet ground in savannah country, around pans and waterholes. Potamonautes calcaratus is the most terrestrial of the freshwater crab species found in South Africa, and lives in burrows it digs near waterholes or pans; it is the only South African freshwater crab to dig a burrow that reaches a depth of 70 cm. During the day it lives in burrows, while at night it leaves its burrows to feed in water or on land. This species moves into open water when it is available during the rainy season.

Links: Notes on the taxonomy of Potamonautes obesus. Reed, S. K. and Cumberlidge, N. Zootaxa 418: 1–20 (2004)

Decapoda, Varunidae

Sat Oct 10, 2015 9:49 am

Family Varunidae
Order Decapoda, Superfamily Grapsidoidea, Family Varunidae

Varunid crabs typically have smooth, squarish or trapezoidal carapaces with the front margin lacking any lobes or teeth. The abdomen of the males rarely covers the whole space between the last pair of legs, and all abdominal segments are movable.

The delimitation of this family, part of the taxonomically confusing Grapsoidea, is undergoing revision. For a long time, they were placed at the rank of subfamily in the Grapsidae.

Most varunid crabs live in the mangrove or mudflats, though some may also be found on drift woods and flotsam out in the sea. Some are known to be able to survive in both fresh and salt water. Their legs are broad and often lined with hair, allowing them to swim for short distances. Varunid crabs are omnivorous, and some have been observe to scavenge.
Like other true crabs, varunid crabs have a broad carapace, and a very short and flattened abdomen which is usually folded underneath the body. They also have five pairs of "legs" (including the clawed arms, or chelipeds), and hence they are placed in the order Decapoda ("deca" means "ten", while "poda" means "feet"). The gills are leaf-like - a distinctive characteristic of decapods from the suborder Pleocyemata. And as with other crustaceans from the class Malacostraca, their body comprises three main parts - a head with five segments, a thorax with eight segments, and an abdomen with six segments. The head is fused to the thorax, forming a cephalothorax. They have a tough exoskeleton strengthened with calcium carbonate, and the carapace covers the gills but not the abdomen.

Varunid crabs reproduce sexually, and have separate sexes. They mate face-to-face, usually with the male on top and the female below. The females can usually be distinguished from the males by having a broader abdomen. This is an adaptation to allow them to carry the eggs under their abdomen until they hatch.

Re: Africa Wild Crustaceans Book (Subphylum Crustacea)

Sat Oct 10, 2015 10:10 am

Brown Shore Crab Cyclograpsus punctatus
Order: Decapoda. Infraorder: Brachyura. Superfamily: Grapsoidea

Image © nan
West Coast National Park

Size: 30 mm CWW
Smooth carapace, which is almost square in appearance. Anterolateral margins of carapace entire; post frontal lobes indistinct, front curving smoothly downwards.
Usually dark brown to dark green in colour, with orange/brown legs and nippers, freckled with darker spots.

Entire South African coastline from Port Nolloth to Natal.

Intertidal zone.

Links: ... le/342/318 ... al&f=false