Africa Wild

Africa Wild Crustaceans Book (Subphylum Crustacea)

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Index to Crustaceans (Subphylum Crustacea)

ORDER: Decapoda (Ten walking legs Prawns, Crabs, Lobsters, Hermit Crabs)

Family Coenobitidae (Terrestrial Hermit Crabs)
Coenobita cavipes Common Land Hermit Crab https://africawild-forum.com/viewtopic.p ... 44#p244344

Family Ocypodidae (Fiddler Crabs and Ghost Crabs)
Subfamily Ocypodinae
Ocypode ryderi Pink Ghost Crab https://africawild-forum.com/viewtopic.p ... 34#p246652
Subfamily Ucinae
Uca sp. Fiddler Crab https://africawild-forum.com/viewtopic.p ... 17#p246617

Family Potamonautidae (River Crabs)
Potamonautes calcaratus Burrowing Feshwater Crab https://africawild-forum.com/viewtopic.p ... 85#p246785
Potamonautes unispinus Single-spined River Crab https://africawild-forum.com/viewtopic.p ... 50#p246650

Family Sesarmidae
Chiromantes eulimene Marsh Crab

Family Varunidae
Cyclograpsus punctatus Brown Shore Crab https://africawild-forum.com/viewtopic.p ... 89#p293789

There are over 40 000 species of crustaceans – four times as many as there are birds. The Crustacea are a subphylum within the Arthropoda that are primarily marine with a few fresh water forms and even fewer are terrestrial. Most prowl around the rocks and reefs – crabs, shrimps and lobsters. The barnacles are static while others such as prawns and krill swim in vast shoals.
The diagnostic character of crustaceans is that they have two pairs of antennae on their heads. The name crustacean is derived from their hard, crusty exoskeleton made from chitin. Although quite diverse, crustaceans are characterised by having three distinct body parts; the head, thorax and abdomen. The head region usually bears a pair of compound eyes and five pairs of appendages (ie., two pairs of sensory antennae and three pairs of mouthparts for feeding). Biramous (Double branched) appendages on the thorax and abdomen are arranged segmentally. One branch is usually the gill branch while the other is the leg branch.
Each species modifies the shapes of its many paired legs for particular purposes, those in front may become pincers or claws: those in the middle can be paddles, walking legs or tweezers, some have feathery gills through which oxygen is absorbed from the water. Others carry the eggs. The limbs are tubular and manyjointed with internal muscles, giving the crustacean great mobility. The external skeleton works almost as well on land as it does in the water so that, providing the creature can find a way of breathing, there is little to prevent it from walking straight out of the waves and up the beach. Sand hoppers, pill bugs and ghost crabs have done just that. The most spectacular of these is the giant robber crab that climbs the trunks of palm trees and chews off coconuts in tropical East Africa.

Crustaceans are classified further based on complex body, carapace and appendage morphology. The Ostracoda or seed shrimps have a carapace shaped like that of a bivalve mollusc, which covers the entire body. The Copepoda or krill are small, often planktonic, lack a carapace, have 4-6 thoracic limbs and no abdominal appendages. The Cirripedia or barnacles have a body enclosed by a shell of calcareous plates. The Malacostraca or shrimp-like or crablike forms have eight pairs of thoracic limbs and usually possess swimming appendages on the abdomen. At present ~2333 crustacean species are known from South Africa.

Ecology
The Crustacea occur in almost every habitat of the marine environment, and are therefore a highly diverse group of organisms. Small crustaceans like copepods and krill feed on green algae. Barnacles, which are attached to various substrata live very inactive lifestyles by filtering the surrounding waters for food. Decopods, which include lobsters, crabs, hermit crabs and shrimp possess a thorax that bears walking legs and either scavenge for food or in some instances capture prey using claws.

Crustaceans are able to form unusual interactions and associations with other organisms. Zooplanktonic crustaceans like copepods and euphausids provide a vital link between the phytoplankton they feed on and larger bodied organisms like pelagic fish, basking sharks, whale sharks and other whales, all of which in turn feed on them. Some barnacles occur exclusively on whales like the goose barnacle, Conchoderma aurita. Hermit crabs are well known for their behaviour of colonizing empty gastropod shells to protect their soft skinned abdomens. When they outgrow their shells they seek out new, larger, ones and on occasion will fight each other for the best shell. Some crabs may be covered in a coat of long, stiff, brown hairs, thereby mimicking a sponge. In fact, they sometimes carry a cloak of sponge, ascidian or seaweed on their backs to ensure that the crabs are unpalatable and well camouflaged from potential predators.

The west coast rock lobster, Jasus lalandii, occurs in shallow water (0-50 m) off the south-western coast from just north of Walvis Bay (Namibia) to about East London on the east coast of South Africa. They are fascinating animals, because they make use of large-scale ocean current systems to transport young away from parent populations, only for the young to return several months later to resettle on “home territory”. This large range is accomplished by the drifting existence of their phyllosoma (”leaf-organism”) larvae. These larvae moult through at least 11 stages, each time adapting to the prevailing environmental conditions, before they metamorphose into a swimming stage known as a puerulus (”little boy”). These transparent miniatures of adult lobsters are capable of swimming long distances thereby returning to the area in which the parent stock lives.

Complex Life Cycles
Crustaceans have complex life cycles. Most have several larval stages that are planktonic and dispersed by currents before they metamorphose into miniature versions of the adults.

Moulting to grow
The external shell presents crustaceans with one problem. It encloses the body completely and will not expand, so it must be shed periodically if the animal is to grow. As the time of moult approaches the animal absorbs much of the calcium carbonate from its shell into its blood. It lays down a soft wrinkled skin beneath the shell. During moulting the outgrown shell splits and the animal crawls out leaving a complete shell, even those parts over the eyes and gills. The soft defenceless creature hides while it grows quickly, swells by absorbing water, and the new shell gradually hardens until the crustacean can venture again into the hostile world. During moulting the animal can regrow any lost limbs or antennae.

Order Decapoda
The decapods or Decapoda (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. The order is estimated to contain nearly 15,000 species in around 2,700 genera, with around 3,300 fossil species. Nearly half of these species are crabs, with the shrimp (about 3000 species) and Anomura (including hermit crabs, porcelain crabs, squat lobsters (about 2500 species), making up the bulk of the remainder.
As the name Decapoda (from the Greek δέκα, deca-, "ten", and πούς / ποδός, -pod, "foot") implies, all decapods have ten legs, in the form of five pairs of thoracic appendages on the last five thoracic segments. The front three pairs function as mouthparts and are generally referred to as maxillipeds; the remainder are pereiopods. In many decapods, however, one pair of legs has enlarged pincers; the claws are called chelae, so those legs may be called chelipeds. Further appendages are found on the abdomen, with each segment capable of carrying a pair of biramous pleopods, the last of which form part of the tail fan (together with the telson) and are called uropods.
Classification within the order Decapoda depends on the structure of the gills and legs, and the way in which the larvae develop, giving rise to two suborders: Dendrobranchiata and Pleocyemata. The Dendrobranchiata consist of prawns, including many species colloquially referred to as "shrimp", such as the "white shrimp", Litopenaeus setiferus. The Pleocyemata include the remaining groups, including "true shrimp". Those groups which usually walk rather than swim (Pleocyemata, excluding Stenopodidea and Caridea) form a clade called Reptantia.

Family Coenobitidae
The Coenobitidae are the family of terrestrial or semiterrestrial hermit crabs, widely known for their terrestrial habits, with 17 species in two genera, including shell-carrying terrestrial hermit crabs (Coenobita spp.) and the monospecific coconut crab Birgus latro.

Primarily distributed in the Indo-Pacific, hermit crabs of the genus Coenobita possess an obsolete rostrum, posterior carapace not much expanded laterally; short and semi-chelate fourth pereopods, antennular flagella truncated at tip. Rostrum almost obsolete; abdomen (pleon) soft, spirally coiled.

Land hermit crabs are scavengers and will consume plants, dead fish, fruit and other detritus.

Common Land Hermit Crab, Concave Land Hermit Crab Coenobita cavipes
Subphylum Crustacea. Order Decapoda. Family Coenobitidae

© Peter Connan
Maphelane, iSimangaliso Wetland Park, KwaZulu-Natal

Description
Size: Length of first part of cephalo-thorax 30-40 mm.
Eyes are elongated and the stalks are mostly black on adults. In juveniles, the lower portion of the stalk is black. Ocular peduncles generally white with broad dark band at midlength and dark brown patch and tinge of blue at base of cornea. Ocular peduncles half shield length or slightly less, corneas only faintly dilated; ocular acicles each with small submarginal spine. Antennular and antennal peduncles overreaching ocular peduncles.
Bottom section of second antenna are orange. Distal two segments of antennular peduncles each with broad band of reddish-brown and tinge of blue distally. Fifth segment of antennal peduncle transparent with brown mesial and lateral stripe. The anntenal aicicle is fused to the second segment of the peduncle.
No stitch marks on large claw. Chelipeds generally brown with capsulate tubercles gray to blue-gray and spines brown to yellowish-brown; meri brown with spots of blue-gray. Chelipeds grossly unequal, both provided with numerous tufts of short or moderately short setae, often concealing armature, palms and carpi also with numerous capsulate setae on dorsal and lateral surfaces; dorsomesial and dorsolateral margins of palm of right cheliped each with row of small spines, dorsal surface with scattered small, often capsulate spines, one more prominent in midline; carpus with row of prominent spines on dorsomesial margin, dorsal surface with scattered capsulate tubercles and small spines, dorsolateral margin not delimited.
Left cheliped with chela elevated in midline but not forming distinct ridge, but armed with row of moderately large spines extending onto proximal half of fixed finger, dorsolateral surface with numerous capsulate tubercles, dorsomesial surface with scattered small spines; dorsomesial margin of carpus with row of large spines, dorsolateral margin only weakly delimited by few small spines.
Third left leg is armored. Ambulatory legs similar; dactyls very slightly shorter to somewhat longer than propodi, ventral margins each with row of 7–10 prominent corneous spines; propodi unarmed but with transverse rows of long setae; carpi each with dorsodistal spine and tufts of long plumose setae. Telson with posterior lobes separated by small median cleft; terminal margins almost straight to very slightly concave, each with row of small spines, interspersed with minute spinules. Ambulatory legs with dactyls brown proximally, white distally; propodi reddish-brown proximally, blue-gray distally; carpi brown to reddish-brown, spotted with blue-gray; meri each brown proximally with large dorsal white patch and blue-gray distally with large dorsal brown patch.

Distribution
Found in the Indo-Pacific region: Eastern Africa, South Africa (east coast), Mozambique, China, Japan, Malaysia, Taiwan, Micronesian, Polynesia, India.

Habitat
Supralittoral zone of sandy beaches. They live inland and only go to the beach to breed and wet their bodies. They bury themselves below the high water mark by day and live within gastropod shells.

Diet
Omnivorous. They are generalist feeders and active scavengers.

Reproduction & Life Cycle
Female hermit crabs have gonophores on their fourth pair of legs. Males fertilise the females by passing spermocytes over these gonophores. To do this, they must both partly emerge from their shells. The female then lays eggs and holds them inside her shell using pleopods. The female broods the eggs for approximately a month before returning to the ocean to release the eggs. The eggs burst and release zoea (planktonic larvae). The zoea remain in the plankton for about two months, constantly going through metamorphosis to become a megalopa. The megalopa finds its first shell and lives both on land and in the water for a month before completing its first moult. After the moult the hermit crab emerges as a juvenile and is completely terrestrial.

Importance
Due to their general scavenging ways and the fact that they are gregarious feeders, they will quickly “clean up” organic waste on the beach, removing the potential for disease.

Links: CoenobitaSpecies.com; Tony's Coenobita; uShaka Sea World

Family Ocypodidae, Subfamily Ocypodinae

Ghost crabs are semiterrestrial crabs of the subfamily Ocypodinae. They are common shore crabs in tropical and subtropical regions throughout the world, inhabiting deep burrows in the intertidal zone. They are generalist scavengers and predators of small animals. The name "ghost crab" derives from their nocturnality and their generally pale coloration. They are also sometimes called sand crabs, though the name refers to various other crabs that do not belong to the subfamily.

Characteristics of the subfamily include one claw being larger than the other, thick and elongated eyestalks, and a box-like body. The differences in claw sizes, however, are not as marked as in male fiddler crabs.

Pink Ghost Crab Ocypode ryderi
Subphylum Crustacea. Order Decapoda. Family Ocypodidae. Subfamily Ocypodinae

© Peter Connan

© Peter Connan
Maphelane, iSimangaliso Wetland Park, KwaZulu-Natal.

© PJL
Eastern Cape, near Port Elizabeth


Identification of Ghost Crabs
The three species found on the east coast, Ocypode ryderi, 0. ceratopthalma and 0. madagascariensis, are difficult to distinguish as juveniles. Of the two dominant species, 0. ceratopthalma occurs mainly in more sheltered localities while 0. ryderi dominates the supralittoral on all open beaches including the sandy beaches in the eastern Cape Province.

Description
Size: width 2.5-3.5 cm
Ghost crabs have a box-shaped carapace, one enlarged nipper and stalked eyes. They five pairs of legs. The first pair is called Chelipeds and is shaped as claws. The legs, when jointly used, can make crabs move in any direction – forward, backward or sideways. In males crabs, one claw is slightly larger than the other. The larger of the two nippers has a granular stridulating organ on the palm which consists of a single row of granules. Ghost crabs have large black eyes that are supported on stalks and can see in any direction.
Ocypode ryderi has a pale pink body and disctinctive red joints on the chelipeds and legs.

Distribution
West Indian Ocean to West Pacific Ocean. In South Africa, Ghost crabs are found on the east coast from East London northwards.

Habitat
They inhabit sandy beaches in the upper intertidal zone and backshore where they burrow gregariously.

Diet
The Pink Ghost Crab is a scavenger, emerging at night to feed on carrion and small animals deposited along the seashore.

Reproduction & Life Cycle
The flap under the abdomen of a male crab is narrow and triangular whereas females have a wider more rounded flap where eggs are incubated. Ghost crabs mature when their carapace is approximately 30 mm wide, a size attained after about one year. Thousands of eggs are produced which are brooded by the female before being released into the sea. These hatch into larvae that spend about two and a half months at sea before returning to the beach.
Ghost crabs grow fairly rapidly, reaching breeding age after a year.

Ecology
These crabs are gregarious animals and can communicate by rubbing a raised ridge on their claw against the base of their arm. They also communicate by the types of burrows and associated sand mounds that they build. Mature male horn-eyed ghost crabs build spiral burrows with pyramid-shaped mounds of sand whereas females do not create sand mounds or build spiral burrows. Intertidal burrows are destroyed by rising spring tides and the crabs dig them out again from the inside when the water recedes. On the long sandy beaches of Maputaland, Palmnut vultures can be seen eating ghost crabs.

Links: The Coastal Guide of South Africa

Family Ocypodidae, Subfamily Ucinae

Fiddler crabs are fossorial, semi-terrestrial crustaceans that live primarily in the littoral zone of protected bays, estuaries and lagoons, and particularly in mangroves. The genus is cosmopolitan, primarily concentrated in the tropics, although the crabs range from as far north as Massachusetts to as far south as South Africa.

They are characterized by strong sexual dimorphism and male asymmetry. Male fiddler crabs exhibit one of the most extreme levels of body asymmetry of any bilateral
organism, having a large major claw (which contains a third to half of the animal’s body mass) and a small minor claw; females have a pair of small claws that resemble the male’s minor claw. The major claw is used for only two functions: display and combat; the minor claw is used for feeding. The waving display of male fiddler crabs serves a function in both male-male aggression and male-female species recognition and mate choice.

Uca spp.
These crabs are easily identified by the male’s one pronounced and vividly coloured cheliped, used for mating rituals and territorial displays.
Females’ chelipeds are both of the same size and are much smaller than the enlarged cheliped of the male. The chelipeds are used to shove food into the mouth. The fiddler crabs feed on organic detritus and plankton deposited on the sand and mud surfaces. Adapted mouth parts sort the food particles from the sediment – food is swallowed while sediment is deposited as small round pellets. Males use only the smaller of the two chelipeds for feeding while females alternate.
Fiddler crabs are amphibious, equally home on land and in water. They are rather passive in the water but very active on land and the sideways walk so typical of land crabs can quickly turn into a speedy run.
These crabs are adapted to pick up vibrations on land through minute hairs on their legs and bolt off when they are approached. In the absence of a hiding place they run in a strongly zig-zag pattern of avoidance.
The fiddler crabs have gills for breathing, organised in the usual crustacean manner within a gill cavity below the carapace. These gills are modified for breathing on land – they are small and stiff so they do not adhere together when surrounded by air, losing valuable surface area in the process. The walls of the gill cavity are richly endowed with blood vessels so that they provide supplementary absorptive surfaces. Furthermore the gill cavity is reduced in size and fringed with hairs to limit evaporation from the gill cavity. These adaptations allow the crabs to be out of the water for hours.
Fiddler crabs are burrowers. The burrows are constructed by males and females and play a central role to the crab’s territory as they are in constant use. The burrows always have some water in them and the crab returns for replenishment of water to the gills as well as for refuge during the high tide. The entrance will be plugged with mud to keep some air in the burrows during high tide and to protect them from predators.
After impressive mating displays by the males, using their colourful chelipeds, breeding takes place and the females will carry the eggs on their bodies to protect them until free-swimming larvae hatch.

From South Africa reported:
Uca annulipes
Uca chlorophthalmus
Uca inversa
Uca urvillei
Uca vocans


© Duke
Male Uca sp. possibly Uca chlorophthalmus the Green-eyed Fiddler Crab

Description of Uca (Paraleptuca) chlorophthalmus
Size: 20 mm CWW
Distinguishing features: Broad frontal margin. Bright green/blue and black mottled carapace with red legs and chelae.

Pinkclaw Fiddler Crab, Ring-legged Fiddler Crab Uca annulipes
Subphylum Crustacea. Suborder Brachyra. Order Decapoda. Family Ocypodidae. Subfamily Ucinae

© Duke
uMlalazi Nature Reserve, KwaZulu-Natal North Coast

Description
Size: 20 mm carapace width
This species is distinguished by broad frontal margin, mottled light-coloured carapace and long, light pink chela in males.

Distribution
Found along the coastline from South Africa to Somalia, Madagascar, India, China, Indonesia, Malaysia and the Philippines. In Soth Africa from Port St Johns to Mozambique.