ABSTRACT
The movements performed by the abdomen and tailfan during tailflipping in the sand crab Blepharipoda occidentalis (family Albuneidae) are described from an analysis of high-speed cinematic film (Figs. 1, 2, 3 A), and compared with component movements in the swimming-by-uropod-beating behaviour of the sand crab Emerita analoga (Family Hippidae) (Fig. 3 B; Paul, 1971). The most striking qualitative difference is the absence of uropod retraction and protraction in Blepharipoda. Comparisons of clectromyo-grams recorded from some of the principal muscles involved in these overtly very different behaviour patterns reveal that homologous muscles in the two sand crabs tend to be activated at comparable phase positions (Table 1). Tailflipping and uropod beating in the two crabs appear to be homologous, and to have been derived from ancestral macruran tailflipping.
