Sesarma sp., copyright Rodrigo Borçato.

Belongs within: Brachyura.
Contains: Grapsinae, Varuninae.

The Grapsoidea are a diverse group of crabs including both terrestrial and aquatic taxa, with the highest diversity in the marine intertidal and supratidal zones. The group is poorly defined but members tend to have a rectangular carapace. Terrestrial adults are found in the families Gecarcinidae and Sesarmidae though only some Sesarmidae do not need to return to the sea to lay eggs.

Getting crabs
Published 27 October 2008
The purple shore crab Leptograpsus variegatus of the southern subtropical Indo-Pacific ocean. Photo by Benjamint444.

When I was but an ickle lad, and my family would camp over Christmas at the beach by the estuary beneath the house of my great-grandparents, I would spend many hours turning over rocks and catching the crabs that I found underneath them. The most common variety I would find was the tiny grey-brown mud crab Helice crassa, which could be handled easily, but if I managed to turn over one of the really big rocks then I would be able to find the larger purple shore crabs Leptograpsus variegatus, which required a more careful approach lest they inflict great pain. One thing I didn’t know at the time about either animal, however, was that they were both members of the superfamily Grapsoidea.

Grapsoidea is a grouping of crabs including at least seven families. The classification of Grapsoidea is currently undergoing something of a revision, and has shifted about a little in recent years. While most grapsoids were once included in the single family Grapsidae, the recognition of the latter as paraphyletic to the Gecarcinidae has lead to the elevation of the various prior subfamilies of Grapsidae to separate families. The family Glyptograpsidae was only established in 2002 (Schubart et al. 2002), while the genus Xenograpsus was moved into its own family within the past year (Ng et al. 2007). Other families in the group are Sesarmidae, Varunidae and Plagusiidae. The majority of grapsoids are found on the shoreline, but some (such as the Chinese mitten crab Eriocheir sinensis) move into fresh water. At least one genus, Planes (Grapsidae), is pelagic, while Xenograpsus has been found to depths of 270 m (McLay 2007). Xenograpsus is found in association with hydrothermal vents, and populations of X. testudinatus living on sulphur vents near Taiwan make their living by feeding on the rain of dead zooplankton killed by toxic discharges from the vents (Ng et al. 2007).

Gecarcoidea natalis, Christmas Island red crab migration. Photo from here.

Some members of the Gecarcinidae live their adult lives terrestrially as adults on tropical islands. Nevertheless, all grapsoids (as far as I can tell) retain the ancestral state of marine planktonic larvae, so all terrestrial gecarcinids must return to the coast to spawn. The Christmas Island red crab, Gecarcoidea natalis has become renowned for the vast numbers that can be seen in its mass migrations, as the entire island’s population of crabs (more than 40 million when estimated in 1995—Adamczewska & Morris 2001) moves down to the coast over the course of a week or so. Tragically, recent years have seen a population explosion on Christmas Island of the introduced yellow crazy ant* Anoplolepis gracilipes which was estimated to have killed off some 15 million-plus crabs by 2003 (O’Dowd et al. 2003), and has essentially eliminated crab populations wherever it has established colonies. Foraging crabs are attacked in large numbers by crazy ants defending their nests, and poisoned with large amounts of formic acid. Crazy ants will also occupy crab burrows, removing their former inhabitants with extreme prejudice. Not only are resident crabs killed, but crabs migrating from elsewhere have been destroyed as they crossed crazy ant-infested locations on their way to the coast. Where red crabs have been eliminated, the forest vegetation structure has begun to change significantly, as seedlings that would have once been grazed by crabs are able to establish a dense undergrowth.

*So called because of the seemingly random way in which they wander about when foraging.

Xenograpsus testudinatus at the base of a sulphur vent. Photo from here.

The Grapsoidea are closely related to another shore-crab family, the Ocypodoidea, and apparently species included in these two superfamilies were once united (back in the 1800s) under the taxon name Catometopa (Schubart et al. 2006), a name that I think deserves resurrection (just try saying it a couple of times—”Catometopa!”). While it seems to be universally accepted that these two superfamilies form a clade, the molecular phylogenetic analysis of Schubart et al. (2006) indicated that each of the “superfamilies” was polyphyletic within this clade, and recommended that they not be recognised as distinct. So far, I haven’t been able to find what are the characters that are supposed to separate the two groups. Davie & Ng (2007) stated that morphological data maintained the monophyly of Grapsoidea, but omitted to cite any details in support of this statement.

Systematics of Grapsoidea
    |    |--Platychirograpsus spectabilis de Man 1896 [incl. P. typicus Rathbun 1914, Areograpsus typicus Krøyer ms]SCF02
    |    `--GlyptograpsusSCF02
    |         |--G. impressus Smith 1870 [incl. G. spinipes Cano 1889]SCF02
    |         `--G. jamaicensis (Benedict 1892) [=Areograpsus jamaicensis]SCF02
    |    |  i. s.: Palaeograpsus Bittner 1875BWW93
    |    |         MetopograpsusJ90
    |    |           |--M. messor (Forskål 1775)J90
    |    |           `--M. quadridentatusGLT03
    |    |         Aratus Milne-Edwards 1853B55
    |    |           `--A. pisonii (Milne-Edwards 1837) [=Sesarma pisonii]B55
    |    |         Sesarmoides Serène & Soh 1970H86
    |    |           |--S. cerberus (Holthuis 1964)H86
    |    |           |--S. jacobsoni (Ihle 1912)H86
    |    |           `--S. verleyi (Rathbun 1914)H86
    |    |         Goniopsis De Haan 1833B55
    |    |           `--G. cruentata (Latreille 1803) [=Grapsus cruentatus]B55
    |    |                |--G. c. cruentataB55
    |    |                `--G. c. pulchra (Lockington 1876) [=Goniograpsus pulcher]B55
    |    |--GrapsinaeSCF02
    |    `--VaruninaeCH03
    |    |--Cardisoma Latreille 1825SCF02, B55
    |    |    |--C. crassum Smith 1870B55
    |    |    `--C. guanhumi Latreille 1825H86
    |    |--Gecarcinus Leach 1814B55
    |    |    |--G. lateralis (de Fréminville 1835)SCF02 [=Ocypoda lateralisB55; incl. G. quadratus Saussure 1853B55]
    |    |    `--G. ruricola (Linnaeus 1758)H86
    |    `--Ucides Rathbun 1897B55
    |         |--U. cordatus (Linnaeus 1763)B55 [=Cancer cordatusB55, Ocypoda cordataL02]
    |         `--U. occidentalis (Ortmann 1897) [=Oedipleura occidentalis]B55
    |    |--Percnon [Percninae]TSH09
    |    |    |--P. abbreviatum (Dana 1851)TSH09
    |    |    |--P. guinotae Crosnier 1965TSH09
    |    |    `--P. planissimum (Herbst 1804)TSH09
    |    `--PlagusiinaeSCF02
    |         |--Euchirograpsus americanus Milne Edwards 1880SCF02
    |         `--PlagusiaSCF02
    |              |--P. chabrus (Linnaeus 1764) (see below for synonymy)B64
    |              |--P. dentipes de Haan 1835SCF02
    |              `--P. depressa [=Grapsus (Plagusia) depressus]G20
    |                   |--P. d. depressaJ90
    |                   `--P. d. tuberculata Lamarck 1818J90
    `--Sesarmidae [Sesarminae]SCF02
         |--Armases ricordi (Milne Edwards 1853)SCF02
         |--Epigrapsus politusB64
         |    |--C. buettikoferi de Man 1883SCF02
         |    `--C. haematocheir (de Haan 1835)SCF02
         `--Sesarma Say 1817B55
              |  i. s.: S. bidentatum Benedict 1892H86
              |         S. catenataB64
              |         S. rectumHN-F08
              |         S. reticulatum (Say 1817)SCF02
              |         S. roberti Milne Edwards 1853H86
              |         S. smithiiF71
              |--S. (Sesarma) sulcatum Smith 1870 [=S. sulcata]B55
              `--S. (Holometopus)B55
                   |--S. (H.) angolensePB27
                   |--S. (H.) angustum Smith 1870 [=S. angusta]B55
                   |--S. (H.) buettikoferiPB27
                   |--S. (H.) miersii Rathbun 1897B55, H86
                   |--S. (H.) occidentalis Smith 1870 [incl. S. (H.) biolleyi Rathbun 1906]B55
                   `--S. (H.) tampicense Rathbun 1914B55

Plagusia chabrus (Linnaeus 1764) [=Cancer chabrus; incl. P. capensis Balss 1935, Marestia mawsoni Rathbun 1918]B64

*Type species of generic name indicated


Adamczewska, A. M., & S. Morris. 2001. Ecology and behavior of Gecarcoidea natalis, the Christmas Island red crab, during the annual breeding migration. Biological Bulletin 200: 305–320.

[B64] Bennett, E. W. 1964. The marine fauna of New Zealand: Crustacea Brachyura. New Zealand Department of Scientific and Industrial Research Bulletin 153: 1–120.

[B55] Bott, R. 1955. Dekapoden (Crustacea) aus El Salvador. 2. Litorale Dekapoden, außer Uca. Senckenbergiana Biologica 36: 45–70.

[BWW93] Briggs, D. E. G., M. J. Weedon & M. A. Whyte. 1993. Arthropoda (Crustacea excluding Ostracoda). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 321–342. Chapman & Hall: London.

[CH03] Chu, K. H., H. Y. Ho, C. P. Li & T.-Y. Chan. 2003. Molecular phylogenetics of the mitten crab species in Eriocheir, sensu lato (Brachyura: Grapsidae). Journal of Crustacean Biology 23 (3): 738–746.

Davie, P. J. F., & N. K. Ng. 2007. Two new subfamilies of Varunidae (Crustacea: Brachyura), with description of two new genera. Raffles Bulletin of Zoology Supplement 16: 257–272.

[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1–167.

[GLT03] Glenner, H., J. Lützen & T. Takahashi. 2003. Molecular and morphological evidence for a monophyletic clade of asexually reproducing Rhizocephala: Polyascus, new genus (Cirripedia). Journal of Crustacean Biology 23: 548–557.

[G20] Goldfuss, G. A. 1820. Handbuch der Naturgeschichte vol. 3. Handbuch der Zoologie pt 1. Johann Leonhard Schrag: Nürnberg.

[HN-F08] Hirose, G. L., & M. L. Negreiros-Franzoso. 2008. Growth and juvenile development of Uca maracoani Latreille 1802-1803 in laboratory conditions (Crustacea, Decapoda, Brachyura, Ocypodidae). Senckenbergiana Biologica 88 (2): 161–168.

[H86] Holthuis, L. B. 1986. Decapoda. In: Botosaneanu, L. (ed.) Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) pp. 589–615. E. J. Brill/Dr W. Backhuys: Leiden.

[J90] Jones, D. S. 1990. Annotated checklist of marine decapod Crustacea from Shark Bay, Western Australia. In: Berry, P. F., S. D. Bradshaw & B. R. Wilson (eds) Research in Shark Bay: Report of the France-Australe Bicentenary Expedition Committee pp. 169–208. Western Australian Museum.

[L02] Latreille, P. A. 1802. Histoire Naturelle, générale et particulière des crustacés et des insectes vol. 3. Familles naturelles des genres. F. Dufart: Paris.

McLay, C. 2007. New crabs from hydrothermal vents of the Kermadec Ridge submarine volcanoes, New Zealand: Gandalfus gen. nov. (Bythograeidae) and Xenograpsus (Varunidae) (Decapoda: Brachyura). Zootaxa 1524: 1–22.

Ng, N. K., P. J. F. Davie, C. D. Schubart & P. K. L. Ng. 2007. Xenograpsidae, a new family of grapsoid crabs (Crustacea: Brachyura) associated with shallow water hydrothermal vents. Raffles Bulletin of Zoology Supplement 16: 233–256.

O’Dowd, D. J., P. T. Green & P. S. Lake. 2003. Invasional ‘meltdown’ on an oceanic island. Ecology Letters 6 (9): 812–817.

[PB27] Pilsbry, H. A., & J. Bequaert. 1927. The aquatic mollusks of the Belgian Congo, with a geographical and ecological account of Congo malacology. Bulletin of the American Museum of Natural History 53 (2): 69–602, pls 10–77.

Schubart, C. D., S. Cannicci, M. Vannini & S. Fratini. 2006. Molecular phylogeny of grapsoid crabs (Decapoda, Brachyura) and allies based on two mitochondrial genes and a proposal for refraining from current superfamily classification. Journal of Zoological Systematics and Evolutionary Research 44 (3): 193–199.

[SCF02] Schubart, C. D., J. A. Cuesta & D. L. Felder. 2002. Glyptograpsidae, a new brachyuran family from Central America: larval and adult morphology, and a molecular phylogeny of the Grapsoidea. Journal of Crustacean Biology 22 (1): 28–44.

[TSH09] Titelius, M. A., A. Sampey & C. G. Hass. 2009. Crustaceans of Mermaid (Rowley Shoals), Scott and Seringapatam Reefs, north Western Australia. Records of the Western Australian Museum Supplement 77: 145–176.


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