FAO Species Identification Guide for Fishery Purposes Western

Calappidae 1091
Calappidae CALAPPIDAE
Box and moon crabs
Diagnostic characters (principal family characters): Carapace circular or ovate to transversely ovate
or subovate; frontal margin triangular, narrow. Merus of third maxillipeds distinctly triangular.
Opening for afferent respiratory current at base of chela, no canal present along sides of buccal
cavern (even when third maxillipeds pushed aside). Male abdominal segments 3 to 5 completely fused;
male genital openings always coxal.
Subfamily Calappinae (box crabs): carapace circular or subcircular to transversely ovate or subovate;
dorsal surface strongly convex longitudinally and transversely, smooth to granular, and ridged; anterolateral
margins armed with numerous small teeth and lobes, posterolateral parts of carapace sometimes
strongly expanded to form a clypeiform structure (= expanded posterior edge) which at least partially
conceals the legs. Chelae laterally flat-
right chela with
tened, dorsal margin with high, multiden-
specialized tooth
tate crest, right (larger) chela with special
tooth on base of pollex for peeling gastropods,
left chela with forceps-like fingers.
Legs smooth, laterally flattened to varying
degrees but never paddle-like.
right chela
specialized
cutting tooth
Subfamily Matutinae (moon crabs): carapace
circular to ovate; dorsal surface usually
almost smooth to granulose; junction of
antero- and posterolateral margins well developed,
often with long spine. Legs distinctly
flattened laterally, last 2 segments
of all legs paddle-like.
triangular front (or rostrum)
triangular merus
of 3rd maxilliped
anterior part of body
Habitat, biology, and fisheries: Burrowing crabs on soft and mud substrates. Most species of minor
commercial importance, with only Calappa lophos, C. philargius, and Ashtoret lunaris being more
commonly seen in markets.
Similar families occurring in the area
Portunidae: may be confused with members of the Matutinae
(also with paddle-like legs and often long lateral spines), but
can be readily distinguished by the following combination of
characters: carapace hexagonal, transversely ovate to transversely
hexagonal; only the last pair of legs paddle-like; meri
of third maxillipeds quadrate.
Dorippidae (non-commercial): also with triangular meri of the
third maxillipeds, but differ by having the last 2 pairs of legs
small, inserted obliquely on carapace and directed upwards
for carrying objects; sides of the carapace never expanded
into a clypeiform process; chelae relatively delicate, never
with specialized teeth for opening mollusc shells.
subfamily Calappinae
subfamily Matutinae
Portunidae
expanded
clypeiform
process
all legs
paddle-like
only last pair of
legs paddle-like