Myomenippe+hardwickii

** Thunder crab ** ** //Myomenippe hardwickii// (Gray, 1831) **

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 * The myth behind the name: Thunder crab **

//Myomenippe hardwickii// or commonly known as the Stone or Thunder crab is a small to medium-sized crab which is usually encountered  in mangroves and intertidal shores . Using its massive and powerful chelipeds (pincers), it can crush its shelled preys such as the bivalves (clams) and gastropods (snails). 1] Legend has it that if it pinches you, the only way for it to release its grip is by a clap of a thunder and hence, the name Thunder crab. However, this is untrue. The best option for the crab to let go of its grip is to place it on the ground near to its hiding place (rock crevices) and eventually, it will release its grip and scurry back to its hiding place. 2]  Nevertheless, it is harmless if you do not handle it.

Therefore, if you are interested to learn more about the Thunder crab, look no further because this site will equip you with the scientific information you need to know about this crab. Not only that, it is also a stepping stone for young aspiring crab biologist out there to gain knowledge about crab biology. Hence, fret not if you are not familiar with the scientific terms used as simple definitions are provided in this site. By the end of this site, hopefully, you will be on your way to becoming a crab biologist!

= Diagnosis = [Identification of species using distinguishable feature]

First and foremost, a crab biologist has to know which features to look for when he or she is going outfield to search for a particular crab species. Every crab species has its own distinguishable features. For example, the number of the teeth (protrusions which can be either sharp or blunt) at the edge of the carapace (shell) or chelipeds (pincers) can tell different crab species apart. Colour, however, is not a good way to diagno se a crab species as colours may vary depending on th e diet of the crabs. As for M. hardwickii, it is relatively easy to spot it due to its distinct eyes.

Under the genus //Myomenippe//, there are two species: //M. hardwickii// and //Myomenippe fornasinii// (Bianconi 1851). 4] //M. fornasinii// does not occur in Singapore but it is widely distributed in the Northern coast of Australia. 5] The closest relative to //M. hardwickii// that can be found in Singapore is //Menippe rumphii// (Fabricius 1798) commonly known as the Maroon Stone crab, which is under the same family Menippidae as //M. hardwickii//.

 //M. hardwickii// has a distinguishable feature to tell it apart from other similar species. It has bright green eyes  surrounded by a ring of red  and it is often mistaken for //M. rumphii// which has all red eyes. 1]





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=**<span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;">Description **= <span style="color: #0c3c85; font-family: Arial,Helvetica,sans-serif; font-size: 110%; line-height: 1.5;">[Morphological (physical) description of species]

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%; line-height: 1.5;">After identifying the crab, the next thing a crab biologist should know is to describe the crab's morphological (physical) features. For example, he or she should know if a crab species has hairy walking legs or unequal size of chelipeds (pincers). The parts of //M. hardwickii// are labelled and described in a table form below.



- hexagonal (six-sided) - broader than long (width can reach up to 12cm) - convex - smooth texture covered with numerous tiny granules || - surface of two antero-lateral gastric regions is broken into two low granular convexities (bulges)
 * ** Eyes ** || - green eyes, often ringed with red ||
 * ** Carapace **
 * (shell) ** || - colour ranging from dirty brown, reddish brown to greenish brownish yellow (depends on diet)
 * ** Gastric region **
 * (location of stomach) ** || - divided into three regions

|| - each lobe has three teeth ( T )
 * ** Frontal margin **
 * (area between the eyes) ** || - divided into two lobes which is separated by a notch ( N ) (depression) in between

|| - rugose (wrinkled) - covered with four rather distant teeth ( T ) - first three teeth (nearer to the front) are relatively broad and the last teeth is narrow
 * ** Antero-lateral margin **
 * (sides of the carapace facing the front) ** || - thin and sharp

|| - both of unequal sizes with one a little larger than the other - curved carpus - short and stout black fingers - covered with tiny granules || - slender - upper border of last four joints and the lower border of last two joints are abundantly fringed with fine stiff setae (hairs) <span style="font-family: Arial,Helvetica,sans-serif; font-size: 70%; vertical-align: super;">6]
 * ** Chelipeds **
 * (pincers, pereopod 1) ** || - massive
 * ** Walking legs **
 * (pereopods 2-5 or P2-P5 ) ** || - rough surface

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=<span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;">Biology =

The morphology of the crab usually reflects the biology and behaviours of a crab species. Therefore, a crab biologist will learn how //M. hardwickii// makes use of its unique physical features in its daily life and for survival purposes.

Feeding and diet
==== // M. hardwickii // captures its prey which includes snails, clams and jellyfish. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 70%; vertical-align: super;">7] It uses its strong chelipeds to crush the prey, especially those with hard shells such as snails and clams. 2] <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;">The larger cheliped has higher crushing power than the smaller cheliped; hence, it would use the former to crush the prey with harder shells and feed on the meat. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 70%; vertical-align: super;">8] <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;">It also uses its hairy legs to gather smaller pieces of food beneath it and brings it towards its mouth (personal observation).

Movement
//M. hardwickii// is a non-swimming crab as its last pair of pereopods (pereopod 5) is slim and not designed like a broad paddle shape to swim like other swimming crabs. In addition, it moves or walks rather slowly (personal observation).

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Defense mechanism
[Methods to protect the species from predators]

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;"> Usually, when a rock is lifted up in rocky shores, crabs will scatter around to seek refuge in other hiding crevices. However, unlike other crabs, //M. hardwickii// will ‘cuddle up’ by tucking its limbs under its body and <span style="color: #421cd9; font-family: Arial,Helvetica,sans-serif; font-size: 120%;">play dead <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;"> when predators discover its hiding place (lifting the rocks). Therefore, predators will be fooled by its ‘stone appearance’ camouflage and target other scurrying crabs. In addition, it can resist from being pulled out by predators by <span style="color: #421cd9; font-family: Arial,Helvetica,sans-serif; font-size: 120%;">pushing its strong chelipeds and bodies against the rock crevices <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;">. 2] Furthermore, it will also spread both its chelipeds outwards from its body to threaten to pinch the predator (personal observation).

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= Ecology = <span style="color: #0c3c85; font-family: Arial,Helvetica,sans-serif; font-size: 14px;">[Interactions between species and environment]

After learning about its biology, a crab biologist should also know if the crab species' way of life suits for which type of environment and whether they are of any use to people, as well as, if its population numbers are in great danger.



Habitat
<span style="color: #0c3c85; font-family: Arial,Helvetica,sans-serif; font-size: 110%; line-height: 1.5;">[Type of environment where the species live in]

This marine crab species is encountered in a wide range of habitats such as the mangroves, littoral rocky shores, breakwaters, floating fish farms (kelongs), coral rubbles and mussel clumps. //M. hardwickii// can be found hiding in between crevices such as rocks and woods. 1]

Distribution
[Location where the species can be found]

Singapore
In Singapore, //M. hardwickii// is mostly populated in the northern part of Singapore where there is fresh water influence from Sungai Johor (Johor River) that is located north-eastern of Singapore. The crab population can also be located in the western and southern side of Singapore too.

Information on distribution of //M. hardwickii// in Singapore by [|WildSingapore]

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%; line-height: 1.5;">Global
<span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;">//M. hardwickii// is not endemic to Singapore. Globally, the crab species is <span style="color: #421cd9; font-family: Arial,Helvetica,sans-serif; font-size: 120%;">mainly distributed on the coasts facing the Indian Ocean <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;"> and their sightings include the east coast of Africa, Mauritius, east and west coasts of India <span style="font-family: Arial,Helvetica,sans-serif; font-size: 70%; vertical-align: super;">9] <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;">, Taiwan <span style="font-family: Arial,Helvetica,sans-serif; font-size: 70%; vertical-align: super;">10, 11] <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;">and Southeast Asia such as Singapore, Malaysia <span style="font-family: Arial,Helvetica,sans-serif; font-size: 70%; vertical-align: super;">12] <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;">, Thailand (Phuket) <span style="font-family: Arial,Helvetica,sans-serif; font-size: 70%; vertical-align: super;">13] <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;">, Myanmar (Mergui Archipelago) 9] <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;">, Indonesia (Sulawesi) and Borneo. 4]



Human uses
Fishermen will pull out their meaty chelae (claws) for food but the crab is rarely eaten as a whole. 12] A study has shown that the mangrove Thunder crab population in Singapore contains heavy metal contaminants such as mercury (Hg), cadmium (Cd), arsenic (As) and chromium (Cr) and lead (Pb) so it is not for human consumption. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 70%; line-height: 1.5; vertical-align: super;">14]

Threat status
Currently, //M. hardwickii// has not been evaluated yet according to International Union for Conservation of Nature (IUCN) Red List and Singapore Red Data Book. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 70%; line-height: 1.5; vertical-align: super;">15,16] <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%; line-height: 1.5;">However, it was reported that the crab population is susceptible to the rising temperature that is caused by the <span style="color: #421cd9; font-family: Arial,Helvetica,sans-serif; font-size: 120%; line-height: 1.5;">ongoing global warming and climate change <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%; line-height: 1.5;">. 7] <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%; line-height: 1.5;">Therefore, its population numbers will be <span style="color: #421cd9; font-family: Arial,Helvetica,sans-serif; font-size: 120%; line-height: 1.5;">adversely affected <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%; line-height: 1.5;"> if the rate of the rising temperature and sea level does not slow down.

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= Name =

Next, a crab biologist may also wonder how the crab species got its name and who first discovered and described the species. Sometimes, the same species can be described several times using different names like in the case of // M. hardwickii //. For simplicity's sake, common names are also used to describe the species.

**Binomial (scientific) name**: //Myomenippe hardwickii// (Gray, 1831)

**Vernacular (common) name**: Stone crab (English), Mangrove Stone crab (English), Thunder crab (English), Grey-hizumegani (Japanese)



Synonyms
[Other scientific names that have been used to describe the same species but are no longer accepted]


 * //Cancer hardwickii// Gray, 1831
 * //Menippe granulosa// A. Milne-Edwards, 1867
 * //Menippe granulosa// De Man, 1888
 * //Menippe duplicidens// Hilgendorf, 1878

Etymology
[Origin of the species name]

The species epithet of //M. hardwickii// was named after Major-General Thomas Hardwicke who first discovered and collected the crab species which originated from the Indian Ocean. 3] It was then given to <span style="font-family: Arial,Helvetica,sans-serif; font-size: 16px;">Dr John Edward Gray for description of the species (see [|original description]).

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= Taxonomy = <span style="color: #0c3c85; font-family: Arial,Helvetica,sans-serif; font-size: 110%; line-height: 1.5;">[Science of classifying and naming organisms in an ordered system]

A crab biologist should also be familiar with the Linnaean classification system as all living organisms are being grouped according to their similarities using a set of rules. A biologist by the name of Carl Linnaeus started this classification system. He also devised the binomial (two-name) system to describe the species which consists of a genus (a group of related species) and a species epithet. The first letter of the first name which is the genus is capitalised and both the genus and species are italicised as described below.

Taxonavigation
<span style="color: #0c3c85; font-family: Arial,Helvetica,sans-serif; font-size: 110%; line-height: 1.5;">[Classification of the species]

**Kingdom**: Animalia Linnaeus, 1758

**Phylum**: Arthropoda Latreille, 1829

**Subphylum**: Crustacea Brünnich, 1772

**Class**: Malacostraca Latreille, 1802

**Order**: Decapoda Latreille, 1802

**Family**: Menippidae Ortmann, 1893

**Genus**: //Myomenippe// Hilgendorf, 1879

**Species**: //Myomenippe hardwickii// (Gray, 1831)

Taxonomic history
<span style="color: #0c3c85; font-family: Arial,Helvetica,sans-serif; font-size: 110%; line-height: 1.5;">[History of the classification and naming of the species]

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%; line-height: 1.5;"> //M. hardwickii// was originally described as //Cancer hardwickii// by Dr John Edward Gray in 1831. 3]

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= Phylogeny = <span style="color: #0c3c85; font-family: Arial,Helvetica,sans-serif; font-size: 14px;">[Evolutionary history and relationship of the species]

After learning the classification of // M. hardwickii //, a crab biologist may also be curious to find out if the crab species has other closely related species and share common ancestor with other crab species.

To demonstrate the evolutionary process of a certain species, a phylogenetic tree is usually constructed based on either genetic or physical characteristics. The tree is important for biologists to understand the evolution of the species through time and identify closely-related species. The tree which depicts the phylogenetic position of //<span style="font-family: Arial,Helvetica,sans-serif; font-size: 16px;">M. hardwickii // is shown below (in a red box) and it is constructed based on genetic characteristics - <span style="font-family: Arial,Helvetica,sans-serif; font-size: 120%;">three mitochondrial (12S, 16S and COI) and two nuclear genes (18S and Histone 3). The phylogenetic tree below demonstrates that the genus //Myomenippe// is sister group (derived from a common ancestor) to the genus //Menippe//, which includes the species //Menippe adina,// // Menippe mercenaria, //// Menippe nodifrons // and // Menippe // //rumphii.// 17]



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= Type information = <span style="color: #0c3c85; font-family: Arial,Helvetica,sans-serif; font-size: 110%; line-height: 1.5;">[Information on the specimen that was used to first describe the species]

Finally, a crab biologist should also know that type information is important for taxonomists to refer back to when describing the species.

The type locality (location where species was first discovered) of the holotype (specimen that was used to first describe the species) originated from the Indian Ocean and was discovered by Major-General Thomas Hardwicke. The holotype was deposited in the British Museum, London. 3] Back to top

= Links to other online sources =

Click on these links to find out more about the Thunder crab!

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 * [|Encyclopedia of Life (eoL)]
 * [|GenBank]
 * [|Global Biodiversity Information Facility (GBIF)]
 * [|Guide to the Mangroves of Singapore]
 * [|Marine Species Identification Portal]
 * [|National Institute of Oceanography]
 * [|SeaLifeBase]
 * [|The Tide Chaser]
 * [|WildSingapore]
 * [|World Register of Marine Species (WoRMS)]

= Literature cited =

<span style="background-color: #ffffff; font-family: Arial,Helvetica,sans-serif; font-size: small; line-height: 1.5;"> 1. Ng, P.K.L., et al., //Singapore Biodiversity: An Encyclopedia of the Natural Environment and Sustainable Development//. 2011: Editions Didier Millet.

<span style="background-color: #ffffff; font-family: Arial,Helvetica,sans-serif; font-size: small; line-height: 1.5;"> 2. Ng, P.K.L., L.K. Wang, and K.K.P. Lim, //Private lives--an exposÈ of Singapore's Mangroves//. 2008, [Singapore]: Raffles Museum of Biodiversity Research, Dept. of Biological Sciences, National University of Singapore.

<span style="background-color: #ffffff; font-family: Arial,Helvetica,sans-serif; font-size: small; line-height: 1.5;">3. Gray, J., //Description of a new genus, and some undescribed species of Crustacea.// Zoological Miscellany, 1831. **1**: p. 39-40.

<span style="background-color: #ffffff; font-family: Arial,Helvetica,sans-serif; font-size: small; line-height: 1.5;"> 4. Man, d.J., //Zoological Results of the Dutch Scientific Expedition to Central Borneo.// Notes from the Leyden Museum, 1899. **21**(1/3): p. 53-144.

<span style="background-color: #ffffff; font-family: Arial,Helvetica,sans-serif; font-size: small; line-height: 1.5;">5. Tan, M.H., et al., //The complete mitogenome of the stone crab Myomenippe fornasinii (Bianconi, 1851)(Crustacea: Decapoda: Menippidae).// Mitochondrial DNA, 2014(0): p. 1-2.

6. Alcock, A., //The family Xanthidae: the Brachyura Cyclometopa, Pt. I, Material for a carcinological fauna of India, No. 3.// Journal of the Asiatic Society of Bengal, 1898. **67**(11): p. 1.

7. Nguyen, K.D.T., et al., //Upper temperature limits of tropical marine ectotherms: global warming implications.// PLoS One, 2011. **6**(12): p. e29340-e29340.

8. Han, L., et al., //The defensive role of scutes in juvenile fluted giant clams (Tridacna squamosa).// Journal of Experimental Marine Biology and Ecology, 2008. **359**(1): p. 77-83.

9. Chhapgar, B., //On the marine crabs (Decapoda: Brachyura) of Bombay state.// J. Bombay Nat. Hist. Soc, 1957. **54**(2): p. 399-439.

10. Ng, P.K., et al., //An annotated checklist of brachyuran crabs from Taiwan (Crustacea: Decapoda)//. 2001: National Taiwan Museum.

11. Lai, S., I. Huang, and L. Fang, //Crab fauna of Kaohsiung Harbor, southwestern Taiwan.// Ann. Taiwan Mus, 1997. **40**: p. 225-240.

12. Tan, C.G. and P.K. Ng, //An annotated checklist of mangrove brachyuran crabs from Malaysia and Singapore.// Hydrobiologia, 1994. **285**(1-3): p. 75-84.

13. Ng, P.K. and P.J. Davie, //A checklist of the brachyuran crabs of Phuket and western Thailand.// Phuket Marine Biological Center Special Publication, 2002. **23**(2): p. 369-384.

14. Cuong, D.T., et al., //Heavy metal contamination in mangrove habitats of Singapore.// Marine Pollution Bulletin, 2005. **50**(12): p. 1732-1738.

15. <span style="background-color: #ffffff; font-family: arial,verdana,sans-serif;">IUCN Red List of Threatened Species (2015). //Myomenippe hardwickii.// Retrieved from <span style="background-color: #ffffff; font-family: Arial,Helvetica,sans-serif; font-size: small;">http://www.iucnredlist.org/search.

<span style="background-color: #ffffff; font-family: Arial,Helvetica,sans-serif; font-size: small;">16. <span style="font-family: Arial,Helvetica,sans-serif;">Davison, G.W., P.K. Ng, and H.C. Ho, //The Singapore red data book: Threatened plants & animals of Singapore//. 2008: Nature Society.

<span style="background-color: #ffffff; font-family: Arial,Helvetica,sans-serif; font-size: small;">17. <span style="font-family: Arial,Helvetica,sans-serif;">Lai, J.C., et al., //Phylogeny of eriphioid crabs (Brachyura, Eriphioidea) inferred from molecular and morphological studies//. Zoologica Scripta, 2014. 43(1): p. 52-64.

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