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Males have one chela of the female type, but the other is enormously enlarged (Fig. 11), often brightly colored, and used for combat and display (see Chapter 4). 3. The distribution of species in some of the genera of land crabs Number of species Genus East Atlantic West Atlantic East Pacific Coenobita Birgus Cardisoma Epigrapsus Gecarcinus Geograpsus Uca Ocypode 1 0 1 0 1 1 1 1 0 1 0 3 1 15 1 1 0 1 0 3 1 31 2 2 Indo-West Pacific 8 1 4 2 0 3 18 15 + podid habit of remaining burrowed at high tide, and emerging to forage only when uncovered.

Rotundum • C. arm a turn A C. longipes Fig. 5. The distribution of the African and Asian species of Cardisoma. ) Evolution, systematics, and distribution 23 • Cardisoma crassum u Cardisoma guanhumi • Gecarcinus lateral is o Gecarcinus rurico/a * Gecarcinus malpilensis A Gecarcinus planatus Gecarcinus lagostoma Fig. 6. The distribution of the American species of the Gecarcinidae. ) C. rotundum (Quoy and Gaimard). Islands of the Indo-West Pacific from Mauritius eastward. Complete details of the geographical distribution of these species, as well as detailed morphological descriptions, are to be found in Turkay (1970, 1973b, 1974), and in Turkay and Sakai (1976).

4B) and reduced in Epigrapsus. There are some tufts of setae related to water uptake between the bases of the second and third legs in Epigrapsus, and between the base of the abdomen and the fifth leg in Gecarcinus and Gecarcoidea. Otherwise they appear typical brachyurans, and there are no striking features to differentiate the genera. They are mediumto large-sized crabs, and a large Cardisoma exceeds 100 mm in carapace width. A striking phenomenon in gecarcinids is that the breeding migration to the sea is highly synchronized on a lunar and seasonal basis, so that mass movements of the crabs occur.