FAO Species Identification Guide for Fishery Purposes Western

1136 Crabs
Majidae MAJIDAE
Spider crabs
Diagnostic characters: Carapace pyriform
(pear-shaped), circular to subovate,
anterior 1/2 to 1/3 usually distinctly
narrower than posterior part; dorsal surface
gently convex, spinulose, granulose, and/or
ridged; front narrow, often with 2 long horn-like
projections (rostra); orbits poorly developed
to absent; anterolateral margins of carapace
often armed with well-developed spines. Legs
spinulose and/or granulose, often with stiff setae.
All male abdominal segments usually
freely movable in most species.
Habitat, biology, and fisheries: 1/ orbits incomplete
Benthic
crabs. Most species of minor or no importance
to fisheries, with only the larger species of
Schizophrys being occasionally collected in the
Western Central Pacific.
Similar families occurring in the area
None. The generally pyriform (pear-like) shape of many majids easily distinguishes them from other families.
Their orbits are usually poorly demarcated to incomplete and this feature is often quite diagnostic. In
addition, many species have hook-like setae on their bodies and appendages with which they use to attach
various materials for camouflage.
The Hymenosomatidae (crown crabs, non-commercial) closely resemble many majids, but are easily
distinguished by their very small size (small species at 2 mm adult carapace width, being contenders with
the pinnotherids for the smallest crabs in the world), the absence of hook-like setae, and having only 5
abdominal segments (excluding the telson).
Key to species of interest to fisheries occurring in the area
1a. Two accessory spines at base of
each rostral horn (Fig. 1a) . . .
. . . . . . . . . . . . . . Schizophrys dama
1b. One accessory spine at base of
each rostral horn (Fig. 1b) . . .
. . . . . . . . . . . . . . Schizophrys aspera
List of species of interest to fisheries occurring in the area
The symbol is given when species accounts are included.
Schizophrys aspera (H. Milne Edwards, 1834)
Schizophrys dama (Herbst, 1804)
horn-like projections
1 assessory
spine
2 assessory
spines
pyriform
carapace
a) Schizophrys dama b) Schizophrys aspera
Fig. 1 rostral horn (dorsal view)
References
Griffin, D.J.G. 1966. A review of the Australian majid spider crabs (Crustacea, Brachyura). Australian Zoologist,
13:259-298.
Griffin, D.J.G. and H.A. Tranter. 1986. The Decapoda Brachyura of the Siboga Expedition. VII. Majidae. Siboga Exped.
Monogr., 39c(4):1-335.
1/ The most important majids in fisheries are the large crabs of the genus Chionoecetes which occur in cold northern
waters only. Near the area, the “Japanese giant spider crab” (Macrocheira kaempferi), known only from Japan and
Taiwan Province of China, is occasionally collected for food. This is the largest crab in the world, reaching a carapace
width of 30 cm and with legs spanning 2.5 m from tip to tip. The only other majid crab of fishery importance near the
area is the southern spider crab (Jacquinotia edwardsii) from New Zealand, with several tonnes a month being landed.