Seaweed crab Paramithrax peroni, from McLintock 1966.

Belongs within: Heterotremata.
Contains: Leptomithrax.

The Majidae, spider crabs, are a group of crabs with highly mobile chelipeds that may commonly be used to attach algae and debris to themselves for camouflage.

Majids: crabs with stylish hats
Published 13 August 2013
Aggregation of large spider crabs Leptomithrax gaimardii, photographed by Peter Fuller.

The subjects of today’s post, the Majidae, commonly go by the names of spider crabs or decorator crabs. The first of those names might sound like some people’s ultimate nightmare, but I doubt that anyone could complain about the latter. Majids are characterised by having a carapace longer than wide, often with a covering of bristly hooked setae and relatively long legs (hence the name ‘spider crab’). They get their alternate name of ‘decorator crab’ from the habit of many species of using the aforementioned hooked setae to attach algae and other bits of organic matter to themselves. The primary purpose of this adornment is to provide camouflage, and a decorated spider crab can be inordinately difficult to see when not moving. A secondary use of the crab’s organic covering, however, is that they will also feed on material from it in times of need*.

*It is perhaps fortunate for Gaga that the question was never raised of her doing the same.

Triangle crab Eurynolambrus australis, from here.

The circumscription of the Majidae is more than a little fluid: at times, it has been used to include all the spider crabs of the superfamily Majoidea, but the more common practice these days is to divide the majoids between a number of families. Unfortunately, authors have disagreed about what those families should be. Ng et al. (2008) united the subfamilies Majinae and Mithracinae within the Majidae on the basis of shared features such as a well-developed protective orbit around the eyestalk. However, a direct relationship between majines and mithracines is not currently supported by molecular (Hultgren & Stachowicz 2008) or larval (Marques & Pohle 1998) data, though both these latter data sources are themselves limited by the relatively small number of studied taxa. Two smaller subfamilies included by Ng et al. (2008) in the Majidae, the Planoterginae and the isolated species Eurynolambrus australis, have not yet been analysed molecularly. Eurynolambrus australis is a particularly unusual little majid, so much so that it looks more like a parthenopid than a majid. Eurynolambrus also lacks hooked setae and so does not decorate itself; instead, it relies for disguise on its resemblance in colour to the coralline algae amongst which it lives (and on which it primarily feeds, though it is omnivorous overall—Woods & McLay 1996). Ng et al. placed it in the Majidae nevertheless owing to the resemblance of its larval stages to those of Majinae.

Channel clinging crab Mithrax spinosissimus, photographed by Nick Hobgood.

The two main subfamilies, the Majinae and Mithracinae, can be distinguished by the development of the orbit around the eyestalk. In the Mithracinae, the orbit is broadly expanded both above and below (with the lower margin formed from an expansion of the basal antennal segment), almost entirely enclosing the eyestalk and giving the front of the carapace a distinctly broad appearance in dorsal view. In the Majinae, the basal antennal segment is not expanded to form an underside to the orbit, so the eyestalks are contained from above only (Davie 2002). The Majinae are most diverse in the Indo-West Pacific, with only a handful of genera found outside this region. Some majines are quite large: the Australian Leptomithrax gaimardii reaches a leg-span of about 70 cm. The Mithracinae are more pantropical inhabitants of shallow water reefs.

Systematics of Majidae

Characters (from Bennett 1964): Chelipeds especially mobile, rarely much greater than other legs or with fingers bent at angle on hand. Second joint of antenna well developed, generally fused with epistome and often with front. Orbits generally more or less incomplete. Hooked hairs almost always present. Male apertures coxal. Palp of external maxillipeds articulated wither at summit or at antero-internal angle of merus.

<==Majidae [Periceridae, Periceroida]
    |--Stenocionops Desmarest 1823BWW93 [OphthalmiinaeB64, Stenocionopoida]
    |--Micippoides [Hyasteniinae]B64
    |    `--M. angustifrons Milne-Edwards 1873 [incl. Hyastenus andrewsi Calman 1909]JG19
    |    |--SimocarcinusB64
    |    |    |--S. pyramidatus (Heller 1861)J90
    |    |    `--S. simplex (Dana 1852)J90
    |    `--AcanthonyxTF08
    |         |--A. lunulatus (Risso 1816)KK03
    |         `--A. scutiformis (Dana 1851)TF08
    |--Mithracinae [Mithracidae]TSH09
    |    |--Paramicippa spinosaB64
    |    |--Jacquinotia Rathbun 1915 [incl. Prionorhynchus Jacq. in Jacq. & Lucas 1853 (preoc.)]B64
    |    |    `--*J. edwardsi (Jacquinot 1853) [=Prionorhynchus edwardsi; incl. Paramicippa grandis Hector 1899]B64
    |    |--TiariniaTSH09
    |    |    |--T. angusta Dana 1852TSH09
    |    |    |--T. cornigera (Latreille 1825)TSH09
    |    |    |--T. dana Griffin & Tranter 1986HS15
    |    |    |--T. garthi Griffin & Tranter 1986HS15
    |    |    `--T. gracilis Dana 1852HS15
    |    |--MicippaTSH09
    |    |    |--M. cristata (Linnaeus 1758)TSH09
    |    |    |--M. curtispina Haswell 1880J90
    |    |    |--M. excavata Lanchester 1900HS15
    |    |    |--M. philyra (Herbst 1803)J90
    |    |    `--M. thalia (Herbst 1803)KK03
    |    `--Mithrax Latreille 1817GT01
    |         |  i. s.: M. herbsti Risso 1826R26
    |         `--M. (Mithraculus)B55
    |              |--M. (M.) coryphe (Herbst 1785)M88
    |              |--M. (M.) forceps (Milne-Edwards 1875) [=Mithraculus forceps]B55
    |              `--M. (M.) sculptus (Lamarck 1818) [=Maia sculpta]B55
    `--Majinae [Mioida, Mamaiidae]TSH09
         |--Cyclax suborbicularis (Stimpson 1858)TSH09
         |    |--P. banfieldi (McCulloch 1913)HS15
         |    `--P. varians Miers 1879 [=Zewa varians]J90
         |--Campbellia Balss 1930B64
         |    `--*C. kohli Balss 1930B64
         |    |--S. aspera (Milne Edwards 1834)TSH09
         |    `--S. dama (Herbst 1804)J90
         |--Gonatorhynchus Haswell 1880 [incl. Lobophrys Filhol 1886]B64
         |    |--*G. tumidusB64
         |    `--G. barbicornis (Latreille 1828) [=Pisa barbicornis, *Lobophrys barbicornis, Paramithrax barbicornis]B64
         |--Entomonyx Miers 1884MG-H11, B64
         |    |--E. depressus Sakai 1974MG-H11
         |    `--E. spinosus Miers 1884MG-H11 [=Acanthophrys spinosusB64; incl. Macrocoeloma nummifer Alcock 1895B64]
         |--Acanthophrys Milne Edwards 1865 [incl. Chlorinoides Haswell 1879]B64
         |    |--*A. cristimanusB64
         |    |--A. filholi Milne Edwards 1865B64
         |    |--A. goldsboroughi Rathbun 1906B64
         |    |--A. spatulifer (Haswell 1882) [=Paramithrax spatulifer, Chlorinoides spatulifer]B64
         |    `--A. tenuirostris [=*Chlorinoides tenuirostris]B64
         |    |--M. confragosa Griffin & Tranter 1986MG-H11
         |    |--M. crispata Risso 1827KK03
         |    |--M. gibba Alcock 1895MG-H11
         |    |--M. goltziana D’Oliveira 1888KK03
         |    |--M. horridaG20
         |    |--M. squinado (Herbst 1788)DAS03
         |    `--M. suluensis Rathbun 1916MG-H11
         `--Paramithrax Milne Edwards 1834B64
              |--*P. peroni Milne Edwards 1834 [=P. peronii]B64
              |--P. backstromi Balss 1923B64
              |--P. minor Filhol 1886 [incl. P. parvus Borradaile 1916]B64
              |--P. parvispinosus Ward 1933B64
              |--P. pipa (Herbst 1788) [=Cancer pipa, Maja pipa]B64
              |--P. spinosus Miers 1879B64
              `--P. ursus (Herbst 1788) (see below for synonymy)B64
Majidae incertae sedis:
  Hyas Leach 1814GT01
    |--H. alutaceus [=H. coarctatus var. alutacea]S00
    |--H. araneus (Linnaeus 1758) [=Cancer araneus, H. aranea; incl. C. bufo Herbst 1790]S00
    |--H. coarctatus Leach 1815TF08 [=H. coarctataS00; incl. H. serratusS00]
    |    |--H. c. coarctatusG10
    |    `--H. c. ursinus (Rathbun 1924)G10
    |--H. latifrons Stimpson 1857S00
    `--H. lyratusS00
  Microphrys Milne-Edwards 1851B55
    `--M. bicornutus (Latreille 1825) [=Pisa bicornuta]B55
  Planotergum mirabile Balss 1935MG-H11
    |--P. aculeatus (Milne Edwards 1834)HS15
    |--P. albanyensis Ward 1933HS15
    |--P. brevispinosus (Yokoya 1933)MG-H11
    |--P. longispinus (De Haan 1839)HS15
    `--P. occidentalis (Griffin 1970)MG-H11
  Naxia tumidaB64
  Telophrys cristulipesB64
  Mithracia libinoides Bell 1858BWW93
  Naxioides carnarvon Griffin & Tranter 1986J90
  Paranaxia serpulifera (Guérin 1829) [=Naxioides serpulifera]J90
  Paratymolus sexspinosus Miers 1884J90
  Thacanophrys albanyensis (Ward 1933) [=Chlorinoides albanyensis]J90
  Anacinetops stimpsoni (Miers 1879)HS15
  Leptopisa australis Griffin & Tranter 1986HS15

Paramithrax ursus (Herbst 1788) [=Cancer (Mithrax) ursus, Inachus ursus, Maja ursus; incl. P. cristatus Filhol 1886, P. latreillei Miers 1876]B64

*Type species of generic name indicated


[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.

Davie, P. J. F. 2002. Zoological Catalogue of Australia vol. 19.3B. Crustacea: Malacostraca: Eucarida (part 2): Decapoda—Anomura, Brachyura. CSIRO Publishing: Collingwood (Australia).

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

[G10] Grigoryeva, N. I. 2010. Seasonal dynamics of the crab larvae in Minonosok Inlet (Posyet Bay, Peter the Great Bay, the Sea of Japan) in 2000–2004. In: China-Russia Bilateral Symposium: Proceedings of the China-Russia Bilateral Symposium of “Comparison on Marine Biodiversity in the Northwest Pacific Ocean”, 10–11 October 2010, Qingdao (China) pp. 155–164. Institute of Oceanology, Chinese Academy of Sciences; A. V. Zhirmunsky Institute of Marine Biology, Far East Branch of the Russian Academy of Sciences.

[GT01] Guinot, D., & M. Tavares. 2001. Une nouvelle famille de crabes du Crétacé, et la notion de Podotremata Guinot, 1977 (Crustacea, Decapoda, Brachyura). Zoosystema 23 (3): 507–546.

[HS15] Hosie, A. M., A. Sampey, P. J. F. Davie & D. S. Jones. 2015. Kimberley marine biota. Historical data: crustaceans. Records of the Western Australian Museum Supplement 84: 247–285.

Hultgren, K. M., & J. J. Stachowicz. 2008. Molecular phylogeny of the brachyuran crab superfamily Majoidea indicates close congruence with trees based on larval morphology. Molecular Phylogenetics and Evolution 48: 986–996.

[JG19] James, D. J., P. T. Green, W. F. Humphreys & J. C. Z. Woinarski. 2019. Endemic species of Christmas Island, Indian Ocean. Records of the Western Australian Museum 34 (2): 55–114.

[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.

[KK03] Kocataş, A., & T. Katağan. 2003. The decapod crustacean fauna of the Turkish seas. Zoology in the Middle East 29: 63–74.

[M88] Markham, J. C. 1988. Descriptions and revisions of some species of Isopoda Bopyridae of the northwestern Atlantic Ocean. Zoologische Verhandelingen 246: 1–63.

Marques, F., & G. Pohle. 1998. The use of structural reduction in phylogenetic reconstruction of decapods and a phylogenetic hypothesis for 15 genera of Majidae: testing previous larval hypotheses and assumptions. Invertebrate Reproduction and Development 33 (2-3): 241–262.

[MG-H11] McEnnulty, F. R., K. L. Gowlett-Holmes, A. Williams, F. Althaus, J. Fromont, G. C. B. Poore, T. D. O’Hara, L. Marsh, P. Kott, S. Slack-Smith, P. Alderslade & M. V. Kitahara. 2011. The deepwater megabenthic invertebrates on the western continental margin of Australia (100–1100 m depths): composition, distribution and novelty. Records of the Western Australian Museum Supplement 80: 1–191.

Ng, P. K. L., D. Guinot & P. J. F. Davie. 2008. Systema brachyurorum: part I. An annotated checklist of extant brachyuran crabs of the world. Raffles Bulletin of Zoology 17: 1–286.

[R26] Risso, A. 1826. Histoire naturelle des principales productions de l’Europe méridionale et particulièrement de celles des environs de Nice et des Alpes maritimes vol. 5. F.-G. Levrault: Paris.

[S00] Stebbing, T. R. R. 1900. Arctic Crustacea: Bruce collection. Annals and Magazine of Natural History, series 7, 5: 1–16.

[TF08] Teixeira, G. M., V. Fransozo, A. L. Castilho, R. C. da Costa & F. A. d. M. Freire. 2008. Size distribution and sex ration in the spider crab Epialtus brasiliensis (Dana 1852) associated with seaweed on a rocky shore in southeastern Brazil (Crustacea, Decapoda, Brachyura, Majoidea, Epialtidae). Senckenbergiana Biologica 88 (2): 169–175.

[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.

Woods, C. M. C., & C. L. McLay. 1996. Diet and cryptic colouration of the crab Eurynolambrus australis (Brachyura: Majidae) at Kaikoura, New Zealand. Crustacean Research 25: 34–43.

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