Family MAJIDAE Samouelle, 1819

<em>Dorhynchus thomsoni</em> [from Miers 1886: pl. 5 fig. 2]

Dorhynchus thomsoni [from Miers 1886: pl. 5 fig. 2]

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Family MAJIDAE Samouelle, 1819

Compiler and date details

May 2012 - Peter Davie, Queensland Museum, Brisbane

Macrocoelominae Balss, H. 1929. Expedition S. M. Schiff Pola in das Rote Meer. Nördliche und südliche Hälfte 1895/96–1897/98. Zool Ergebn, 36. Decapoden des Roten Meeres, 4. Oxyrhyncha und Schlussbetrachtungen. Denkschriften der Kaiserlichen Akademie der Wissenschaften, Wien, Mathematisch-Naturwissenschaftliche Klasse 102: 1-30 figs 1-9 pl. 1 [8, 16, 20].
Inachoidinae Dana, J.D. 1851. On the classification of the maioid Crustacea or Oxyrhyncha. American Journal of Science and Arts 2 11: 425-434 [432].
Type genus:
Inachoides H. Milne Edwards & Lucas, 1842.
Eurynolambrinae Stevcic, Z. 1994. Contributions to the re-classification of the family Majidae. Periodicum Biologorum 96(4): 419–420.

Taxonomic Decision for Synonymy

Manning, R.B. & Holthuis, L.B. 1981. West African Brachyuran Crabs (Crustacea: Decapoda). Smithsonian Contributions to Zoology No. 306: i-xii, 1-379 figs 1-88, 2 appendices [252]
Stevcic, Z. 1991. Note on some rare and aberrant Australian crabs. The Beagle, Records of the Museums and Art Galleries of the Northern Territory 8(1): 121-134

Introduction

The Majidae is a very diverse group of crabs in Australian waters. They are commonly called 'Spider Crabs' because their swollen bodies and long legs give many species a spider-like appearance. The other widely used name is 'Decorator Crabs', owing to the habit of a large number of species to decorate the carapace and legs with encrusting invertebrate and algal species. Indeed, a common feature of the family is the specially hooked setae that allow easy attachment of epifauna. While many species do not decorate themselves, those that do are masters of disguise, and only an unexpected movement belies their presence on the sea floor. Majids live in a variety of habitats from the low intertidal into the deep sea; most are free-living, but a few species live in ecto-commensal relationships with other invertebrates, and these adopt the colours and patterns of the host for camouflage (for example, Hoplophrys oatesii).

Majiids are highly plastic in form, and this is well reflected by the many and varied attempts at a natural classification. No less than 50 family or subfamily group names have been proposed. In their major revision of the Majidae, Griffin & Tranter (1986a) recognised seven subfamilies and provided a key for their separation. Of these, only the Oregoniinae Garth, 1958, is not represented in Australian waters. Another subfamily, Planoterginae, was erected by Stevcic (1991) to accommodate the monotypic genus Planotergum Balss. Guinot (1978) suggested that there should be a superfamily Majoidea, a view supported by Clark & Webber (1991) who, based on larval evidence, proposed a new classification recognising four major families: Majidae, Inachidae, Oregoniidae, and Macrocheiridae. Subsequently, the Inachoidinae Dana has also been treated as a family in its own right by some authors (see Guinot & Richer de Forges 1997). The family/subfamily structure used here follows that of Ng et al. (2008).

The largest body of work on Australian majids has been that of Desmond Griffin, formerly Curator of Crustacea, and then Director, of the Australian Museum, Sydney. Besides the definitive publication on this family by Griffin & Tranter (1986a), other important contributions include Griffin (1966, 1970a, 1970b, 1973) and Griffin & Tranter (1986b).

Diagnosis

Carapace widest posteriorly, with well-developed branchial regions; typically pyriform (pear-shaped) or triangular, but also may be circular to sub-ovate; dorsal surface more or less convex, smooth to highly ornamented; hooked setae often present on carapace and legs. Front narrow, produced to form rostrum of varied form: typically two long, horn-like projections, more or less fused at base, but in extreme case may be a short, strongly deflexed flat plate. Orbits complete, poorly developed or absent. Basal segment of antenna well developed, usually fused with epistome, and often also with front. Epistome large, buccal cavity quadrate. Palp of third maxilliped articulated either at summit or at antero-internal angle of merus. Anterolateral margins of carapace often armed with well-developed spines. Legs often spiny and/or granular, often with stiff setae. Chelipeds highly mobile; may be long and massive, or greatly reduced and smaller than walking legs. Male and female abdomen of seven free segments, rarely some fused, sometimes segment 6 fused to telson, to form pleotelson. Female genital openings sternal; male openings coxal. G1 greatly exceeding G2 in length.