Changi beach : 07-09-25

The genus Myomenippe includes the species Myomenippe hardwickii (Gray, 1831) and Myomenippe fornasinii (Bianconi, 1851), both of which are commonly known as stone crabs or mangrove stone crabs and are found in the Indo-Pacific region.

Myomenippe hardwickii, also known as the Stone Crab or Thunder Crab, is a common crab species found in rocky and mangrove habitats in Southeast Asia.

Myomenippe hardwickii is distributed throughout the Western Central Pacific, specifically across Southeast Asia, reaching as far as the Philippines.

It is a common inhabitant of rocky shores, mangrove habitats, and areas with fish farms, where it hides in crevices, under driftwood, and in mussel clumps. Recent research has also documented its presence in other parts of the region, including Indonesia and the Odisha coast of India.

The name "Thunder Crab" comes from the mistaken folk belief that it won't release its pincer grip on a finger until a clap of thunder is heard.

M. hardwickii is distinguished by its brown carapace, large pincers, and striking bright green eyes ringed with red. This crab feeds on mollusks and is an opportunistic predator, often hiding in burrows and feigning death when disturbed, which gives it the "Thunder Crab" nickname.

It grows to a significant size, up to 12cm in width, and primarily feeds on shellfish. The crab's common name "Thunder Crab" comes from the folk belief that it only releases its pincer grip with the sound of thunder, 

 a myth.

A generally shy nature, often retreating into holes, it inhabitat in rock crevices, under driftwood, and in mussel clumps along rocky shores, mangroves, breakwaters and artificial structures.

M. hardwickii feeds on shellfish, sea hares, and other marine life, and is an opportunistic predator.

Phylum : Arthropoda

Class : Malacostraca

Order : Decapoda

Suborder : Pleocyemata

Infraorder : Brachyura

Family : Menippidae

Genus : Myomenippe

Species : M. hardwickii

Binomial name : Myomenippe hardwickii

(Gray, 1831)

Changi beach : 07-09-25

Matutidae is a family of crabs, sometimes called moon crabs, adapted for swimming or digging. They differ from the swimming crabs of the family Portunidae in that all five pairs of legs are flattened, rather than just the last pair, as in Portunidae. Crabs in the Matutidae are aggressive predators.

Ashtoret lunaris is the scientific name for the yellow moon crab, also known as the spotted moon crab or box crab, a carnivorous crab species which is a member of the family Matutidae found in the Indo-Pacific region.

Ashtoret lunaris, or the yellow moon crab, is a medium-sized, Indo-Pacific species of carnivorous crab characterized by a beige or yellow carapace with red spots, paddle-shaped leg tips that allow for skimming on the substrate and rapid for burrowing in sand, and a distinctive lateral spine, the legs can also have large, dark blotches.

These nocturnal crabs are typically found in shallow waters, inhabiting sandy shores, coral reefs, and seagrass meadows. They possess a finely grained carapace texture with six dorsal tubercles and a linear posterior tubercle, along with a five-lobed ridge on the palm of their chelipeds.

Sexual Dimorphism : Males have a finely grained ridge on the outer surface of the dactylus (claw), which is absent in females.

Front : Features two straight, lateral lobes and a slightly indented rostrum (projection between the eyes).

A. lunaris is a species of carnivorous crab primarily nocturnal, foraging more actively at night often burrowing in the sand to avoid detection during the day. It feeds on worms, clams, and other small animals.

Ashtoret lunaris has a natural distribution across the Indo-West Pacific, ranging from the Red Sea and East Africa to the Philippines, New Caledonia, Australia, and Japan.

This species can also be found inhabiting the eastern Mediterranean Sea, where it likely colonized via the Suez Canal as a biological invasion. It is a benthic crab that lives in coastal areas with soft substrates, such as sand. It is also documented in various parts of Asia, such as Japan, China, and the Sundarbans of Bangladesh and Singapore.

Phylum : Arthropoda

Subphylum : Crustacea

Class : Malacostraca

Order : Decapoda

Suborder : Pleocyemata

Infraorder : Brachyura

Family : Matutidae

Genus : Ashtoret

Species : A. lunaris

Binomial name : Ashtoret lunaris

(Forskål), 1775

Aratus pisonii, commonly known as the mangrove tree crab, is a species of crab which lives in mangrove trees in tropical and subtropical parts of the Americas, from Florida to Brazil on the Atlantic coast, and from Nicaragua to Peru on the Pacific coast.

It feeds mostly on the leaves of the mangroves, but is an omnivore, and prefers animal matter when possible.

A. pisonii is the only species in the monotypic genus Aratus. The specific epithet pisonii commemorates the Dutch naturalist Willem Piso who travelled in Brazil in 1638 with Georg Marggraf.

The mangrove tree crab is a small species with males averaging about 2 cm (0.8 in) long and females slightly less. The large eyes are set far apart and the carapace is wider at the front than at the back. It is a mottled brown and olive colour which helps the crab to blend in with its surroundings. The legs are either brown or mottled and tufts of black hairs are near their tips. These are pointed, which aids the crab when climbing among the mangrove foliage.

The mangrove tree crab is an omnivore, though the greatest part of its diet is the leaves of the mangrove trees on which it lives. It consumes the epidermis of the leaves and characteristic scraping marks show where it has fed. Even where this crab is uncommon, its consumption may constitute over 90% of the herbivory of mangrove leaves. It also eats organic debris and algae, and opportunistically feeds on carrion and small invertebrates including polychaete worms, nematodes, and foraminiferans. 

They also feed on the decaying tissues of the mangrove roots and on the feces of others of its species. In feeding trials, this crab was found to prefer animal food over plant food. This is unsurprising considering that mangrove leaves are of poor nutritional value, but what is surprising is the high proportion of leaf matter in the crabs' diet. This may be a response to the greater risk of predation in the water than in the canopy.

The mangrove tree crab is preyed on by birds, terrestrial mammals, and larger crabs. It is efficient at evading potential predators, as it can scuttle along branches at the rate of 1 m/sec and can leap to safety in the water below, but there it may become the victim of a predatory fish.

Phylum : Arthropoda

Subphylum : Crustacea

Class : Malacostraca

Order : Decapoda

Suborder : Pleocyemata

Infraorder : Brachyura

Family : Sesarmidae

Genus : Aratus

H. Milne-Edwards, 1853

Species : A. pisonii

Binomial name : Aratus pisonii

(H. Milne-Edwards, 1837)

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 for breeding.

Geosesarma is genus of small freshwater or terrestrial crabs, typically less than 10 mm (0.4 in) across the carapace. They live and reproduce on land with the larval stages inside the egg. They are found from India, through Southeast Asia, to the Solomon Islands and Hawaii.

In the pet trade, they are sometimes called vampire crabs. This has nothing to do with their feeding habits, but rather with the bright, contrastingly yellow eyes of some Geosesarma species.

Geosesarma faustum is a new species to science; only described in 2016. The species name is derived from the Latin for fortunate and lucky; alluding to the circumstances leading to the discovery of the new species. Unlike the common aquatic crabs, this semiterrestrial crab species uses plants that has small water-filled cavities as their habitat. This species only occurs at altitudes higher than 700 m, and are characterized by their quadrate carapace as well as their long and slender ambulatory legs.

The Penang Hill vampire crab (Geosesarma faustum Ng, 2017), whose squarish carapace has sides of about 10 mm, live in the water of the cup-like depressions formed by bromeliads and other plants.

Penang Hill vampire crab Geosesarma faustum Ng, 2017, endemic to one hill, and which finds the water required to complete its life cycle in the small, cup-like water bodies formed by various leafy plants. A tiny crab, high on its own hill, in its own sea of flowers.

HIGHLAND VAMPIRE Crab Geosesarma faustum Global Conservation Status (IUCN): Not Evaluated

​

Phylum : Arthropoda

Subphylum : Crustacea

Class : Malacostraca

Order : Decapoda

Suborder : Pleocyemata

Infraorder : Brachyura

Family : Sesarmidae

Genus : Geosesarma

De Man, 1892

Type species : Geosesarma faustum

Ng, 2017

Freshwater crabs are found throughout the tropical and subtropical regions of the world.

They live in a wide range of water bodies, from fast-flowing rivers to swamps, as well as in tree boles or caves. They are primarily nocturnal, emerging to feed at night, most are omnivores.

The majority of species are narrow endemics, occurring in only a small geographical area. This is at least partly attributable to their poor dispersal abilities and low fecundity, and to habitat fragmentation caused by the world's human population.

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 release thousands of planktonic larvae.

This limits the dispersal abilities of freshwater crabs, so they tend to be endemic to small areas. As a result, a large proportion are threatened with extinction.

More than 1,300 described species of freshwater crabs are known, out of a total of 6,700 species of crabs across all environments.

The total number of species of freshwater crabs, including undescribed species, is thought to be up to 65% higher, potentially up to 2,155 species, although most of the additional species are currently unknown to science.

They belong to eight families, each with a limited distribution, although various crabs from other families are also able to tolerate freshwater conditions (euryhaline) or are secondarily adapted to fresh water.

The phylogenetic relationships between these families is still a matter of debate, so how many times the freshwater lifestyle has evolved among the true crabs is unknown.

The eight families are:

Superfamily Trichodactyloidea

Trichodactylidae (CentralAmerica and South America)

Superfamily Potamoidea

Potamidae (Mediterranean Basin and Asia)

Potamonautidae (Africa, including Madagascar)

Deckeniidae (East Africa and Seychelles) also treated as part of Potamonautidae.

Platythelphusidae (East Africa) also treated as part of Potamonautidae

Superfamily Gecarcinucoidea

Gecarcinucidae (Asia)

Parathelphusidae (Asia and Australasia) nowadays treated as a junior synonym of Gecarcinucidae.

Superfamily Pseudothelphusoidea

Pseudothelphusidae (Central America and South America)

Parathelphusinae is a subfamily of freshwater crabs, which was formerly placed in the family

Parathelphusidae, they are mainly found in South and Southeast Asia, but also found elsewhere in Asia and in Australia.

The family is now considered as a junior synonym of the family Gecarcinucidae, a family of true freshwater crabs.

The Parathelphusinae inhabit rivers, lakes and rice paddies. Some species, for example from the genus Somanniathelphusa, are locally important as food, particularly in Thailand, Mizoram (India), etc. where they are an important ingredient in som tam.

Some others are very rare and close to extinction such as the Parathelphusa reticulata, Singapore's Swamp Forest Crab.

Parathelphusa reticulata, this freshwater crabs can be found in freshwater stream and in well-shaded acid freshwater water and swamp forests with tea-coloured water of low pH (5.0 - 5.5)

It digs burrows by the side of muddy banks. A shy and secretive species, only active nocturnally and very sensitive to torch lightings.

P. reticulata is omnivores and is one of the animals which are endemic to Singapore forests.

The colonisation of fresh water has required crabs to alter their water balance; freshwater crabs can reabsorb salt from their urine, and have various adaptations to reduce the loss of water.

In addition to their gills, freshwater crabs have a "pseudolung" in their gill chamber that allows them to breathe in air. These developments have preadapted freshwater crabs for terrestrial living, although freshwater crabs need to return to water periodically to excrete ammonia.

Parathelphusa reticulata, IUCN Red List as Critically Endangered species.

​

Phylum: Arthropoda

Subphylum: Crustacea

Class: Malacostraca

Order: Decapoda

Infraorder: Brachyura

Family: Gecarcinucidae

Subfamily: Parathelphusinae

Alcock, 1910

Genus: Parathelphusa

Species : P. reticulata

​Ng, 1990

The mangrove horseshoe crab (Carcinoscorpius rotundicauda), also known as the round-tailed horseshoe crab, is a chelicerate arthropod found in tropical marine and brackish waters in India, Bangladesh, Indonesia, Malaysia, Brunei, Singapore, Thailand, Cambodia, Vietnam, China and Hong Kong. It may also occur in Sri Lanka, Myanmar and the Philippines, but confirmed records are lacking.

Despite their name, horseshoe crabs are more closely related to spiders and scorpions (all are in the subphylum Chelicerata) than to crabs.

Recent phylogenetic analysis suggests that horseshoe crabs may themselves be arachnids. The mangrove horseshoe crab is the only species in the  genus Carcinoscorpius.

There are four extant (living) species of horseshoe crab. The biology, ecology and breeding patterns of C. rotundicauda and the two other Asian horseshoe crab species, Tachypleus gigas and Tachypleus tridentatus, have not been as well documented as those of the North American species Limulus polyphemus. All four extant species of horseshoe crabs are anatomically very similar, but C. rotundicauda is considerably smaller than the others and the only species where the cross section of the tail (telson) is rounded instead of essentially triangular.

Horseshoe crabs are commonly known by biologists around the world as a living fossil because they have remained practically unchanged in terms of shape and size for millions of years. Although their physiology has changed over the years, their typical three piece exoskeleton, consisting of a prosoma, opisthosoma, and telson, has remained since the mid-Paleozoic era.

Fossils of horseshoe crabs that have been dated to over 400 million years ago look almost identical to those species that are still alive today. The long existence of this body plan suggests its success. It is estimated that the American species of horseshoe crab diverged from the three Indo-Pacific species approximately 135 million years ago.

The basic body plan of a horseshoe crab consists of three parts: the prosoma, the opisthosoma and the tail (telson).

The prosoma is the large, dome-shaped frontal part at the carapace. The smaller rear carapace with spines on the edge is the opisthosoma. The rear extension that looks like a spike is the telson, which is commonly described as the tail. Uniquely among the horseshoe crabs, the cross section of the tail is rounded. It is essentially triangular in the other species. The tail is used to turn itself right side up when overturned.

The mangrove horseshoe crab is the smallest of the four living species of horseshoe crabs. Like the other species, females grow larger than males.

Uncommon for chelicerates, horseshoe crabs have two compound eyes. The main function of these compound eyes is to find a mate. In addition, they have two median eyes, two rudimentary lateral eyes, and an endoparietal eye on their carapace and two ventral eyes located on the underside by the mouth.

Scientists believe the two ventral eyes aid in the orientation of the horseshoe crab when swimming. Each individual has six pairs of appendages.

The first pair, the chelicerae, are relatively small and placed in front of the mouth. They are used to place food in it. The remaining five pairs of legs are placed on either side of the mouth and are used for walking/pushing. These are the pedipalps (first pair) and the pusher legs (remaining four pairs). Most of the appendages have straight, scissor-like claws, but in males the first and second pair of walking legs have strongly hooked "scissors", which are used for grasping the female during mating. Located behind their legs are book gills. These gills are used for propulsion to swim and to exchange respiratory gases.

This species occurs only in Asia around the Indo-West Pacific region where the climate is tropical or subtropical. These horseshoe crabs can be found to exist throughout the Southeast Asia region in shallow waters with soft, sandy bottoms or extensive mud flats. The mangrove horseshoe crab is benthopelagic, spending most of its life close to or at the bottom of a body of their brackish, swampy water habitat, such as mangroves. This is the habitat for which it gains its common name: mangrove horseshoe crab.

Mangrove horseshoe crabs are selective benthic feeders, feeding mainly on insect larvae, small fish, oligochaetes, small crabs and thin-shelled bivalves.

Lacking jaws, it grinds up the food with bristles on its legs and places it in its mouth using its chelicerae. The ingested food then enters the cuticle-lined oesophagus and then the proventriculus.

The proventriculus is made up of a 'crop' and a 'gizzard'. The crop can expand to fit the ingested food, while the gizzard grinds the food into a 'pulp'. Studies have found that mangrove horseshoe crabs have a strong preference for insect larvae over the other organisms on which it also feeds.

Thousands of the horseshoe crabs are caught by local fishermen. While the crabs have very little flesh, their roe is prized as a delicacy, in Thailand most commonly served as a salad called yam khai maeng da (ยำไข่แมงดา).

There have occasionally been cases of food poisonings or even deaths after consuming the crabs as they were misidentified as another horseshoe crab species, Tachypleus gigas. Unlike larger T. gigas, C. rotundicauda is known to often contain lethal tetradotoxin.

​Blue bloods. Nearly unchanged for hundreds of millions of years, horseshoe crabs blue bloods have some unusual traits. Horseshoe crabs are prized for their blue blood, as it is widely used in biomedical sciences for the development of drugs for diseases like mental exhaustion and gastroenteritis. 

The blood contains a chemical called Limulus amoebocyte lysate (LAL) that can be used to detect pathogens and their endotoxins.

In 1956, medical researcher Fred Bang noticed another strange characteristic: When horseshoe crab blood interacts with endotoxin, cells called amebocytes clot and form a solid mass. Bang realized that these amebocytes—part of the crab’s ancient immune system—could detect deadly bacterial contaminants in the rapidly expanding array of pharmaceuticals designed to enter the human bloodstream.

The helmet-shaped creatures are brought en masse to specialized labs along the U.S. East Coast, where technicians extract the blood from a vein near the heart before returning them to the sea. (Their blue blood comes from the metal copper in their oxygen-transporting proteins, called hemocyanin.)

​

Phylum : Arthropoda

Subphylum : Chelicerata

Order : Xiphosura

Family : Limulidae

Genus : Carcinoscorpius

Pocock, 1902

Species : C. rotundicauda

Binomial name : Carcinoscorpius rotundicauda

(Latreille, 1802)

Crayfish are freshwater crustaceans resembling small lobsters (to which they are related).

They are also known as crawfish, crawdads, freshwater lobsters, mountain lobsters, mudbugs, or yabbies.

Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gilks. Some species are found in brooks and streams where fresh water is running, while others thrive in swamps, ditches, and paddy fields.

Most crayfish cannot tolerate polluted water, although some species such as Procambarus clarkii are hardier. Crayfish feed on animals and plants, either living or decomposing, and detritus.

Cherax quadricarinatus (known by several common names, including Australian red claw crayfish, Queensland red claw, redclaw, tropical blue crayfish, freshwater blueclaw crayfish) is an Australian freshwater crayfish.

C. quadricarinatus is native to permanent freshwater streams, billabongs and lakes on the north coast of the Northern Territory, northeastern Queensland, and Papua New Guinea.

Through translocation by humans, the range has spread down to southern Queensland and into the far north of Western Australia.

C. quadricarinatus is considered an invasive species, and has established feral populations in South Africa, Mexico, Jamaica, Puerto Rico, Indonesia, Zambia,

Malaysia and Singapore. This tropical crustacean is very tolerant of environmental changes, and is primarily a detritivore.

Cherax quadricarinatus is a large bodied crayfish with a blue-green to green color with red and maroon highlights. Adult males have a soft, fleshy, bright red patch on the outer margin of the major chelae. This species also has four long and distinct carinae (ridges) on the dorsal surface of the cephalon.

Cherax quadricarinatus may reach a total length of about 250 mm (9.8 inches) and can reach up to 600 grams (21 oz).

Females, which are smaller than males, spawn 300–800 olive-green eggs per brood, which are fertilised

from a spermatophore which the male has deposited at the base of her walking legs (pereiopods) during mating.

Fertilised eggs are affixed to the female's pleopods, situated on the underside of the tail. Incubation takes approximately six weeks and the newly hatched juveniles rapidly become independent.

C. quadricarinatus is farmed commercially in Queensland and the Northern Territory, and is harvested at between 35–130 grams (1.2–4.6 oz).

C. quadricarinatus has a robust nature with broad tolerances to environmental extremes and is non-aggressive in nature as well as highly fertile, and can therefore be bred in large numbers in captivity. Time to sexual maturity, and therefore harvest size, is somewhere between six and twelve months in optimally farmed conditions.

Cherax quadricarinatus redclaw crayfish eat a wide variety of prey including small aquatic invertebrates (zooplankton), molluscs (aquatic snails), as well as aquatic plants and detritus.

Phylum : Arthropoda

Subphylum : Crustacea

Class : Malacostraca

Order : Decapoda

Suborder : Pleocyemta

Infraorder : Astacidea

Superfamily : Astacoidea

Latreille, 1802 and Parastacoidea Huxley, 1879

Family : Parastacidae

Genus : Cherax

Species : C. quadricarinatus

Binomial name : Cherax quadricarinatus

(Von Martens, 1868)