FAO Species Identification Guide for Fishery Purposes Western

Guide to Families/Key to Brachyura 1061
COENOBITIDAE Page 1154
Land hermit crabs and coconut crabs
Carapace relatively well calcified; eyestalk laterally
flattened; eyes usually held subparallel to each
other. Antennae laterally flattened. Coxae of third
maxillipeds close to each other, without distinct
gap between them. Chelipeds short, stocky, equal
or unequal; when unequal, left chela larger. First 2
pairs of walking legs well developed, last 2 pairs
reduced, third legs chelate. Abdomen bilaterally
asymmetrical, not clearly divided into segments.
Either hermit crabs or distinctly crab-like animals
with abdomen tucked under carapace; uropods
modified into a “rasp” used for clinging interior of
gastropod shells (except in Birgus latro).
Guide Key to to Brachyura Families/Key to KEY Brachyura TO THE FAMILIES OF BRACHYURAN CRABS
Note: the following key covers all marine families of brachyuran crabs recognized in this work, most of which
have been reported from the Western Central Pacific. The 5 families which so far are known only from other
regions of the world have been included in the anticipation that some of them may be recorded in the future
from the area. Wherever possible, external and easily viewed characters are utilized, and in most cases,
no smaller structures have been chosen, such as male gonopods and structures of male and female
genitalia (which are very important in crab classification). Due to the diversity in some families (e.g.
Xanthidae and Goneplacidae), not all their members can be identified to the family level with this key,
although it should work for the majority of species encountered. There are also a number of unusual species,
the familial classification of which is still contentious. For a more comprehensive key, see Sakai (1976) and
Dai and Yang (1991). For the identification of some more difficult species, the only safe way is to send the
sample(s) to an expert of decapod taxonomy.
1a. Only 3 pairs of legs visible, fourth
pair absent (Fig. 1) . . . . . . . . Hexapodidae
1b. Four pairs of legs visible . . . . . . . . . . → 2
2a. Basal segment of eyestalk much
longer than terminal article, from
dorsal view, eyestalk appears to be
2-segmented (Figs 2a and 3) . . . Latreillidae
2b. Basal segment of eyestalk much
shorter than terminal article, from
dorsal view, eyestalk appears to be
unsegmented (Fig. 2b) . . . . . . . . . . . → 3
basal
article
very long
basal article
very short
a) Latreillidae b) other crabs
Fig. 2 eyestalk
last leg strongly
reduced
Fig. 1 Hexapodidae
Fig. 3 Latreillidae
antenna laterally
flattened
eye laterally
flattened
3 rd leg
chelate