(ORF). The C-terminal part of the predicted protein was composed of a trypsin-like serine protease domain, with homology to counterparts in other animals of 33–38%. The predicted protein (54.7·kDa) secreted as a zymogen

Fertilized eggs in a number of decapod crustaceans (except Dendrobranchiata) attach to ovigerous hairs arranged on the abdomen of the female. The attachment is effected by an ‘embryo attachment system’ composed of an egg envelope, funiculus, and the coat that wraps around the hair, and the embryos are ventilated by the female (Herrick, 1895; Yonge, 1937, 1946; Cheung, 1966; Goudeau and Lachaise, 1983; Goudeau et al., 1987; Saigusa et al., 2002). On completion of embryonic development, the egg case is broken, and zoea larvae hatch. Hatching in most crustaceans differs greatly from that of other animals. It is characterized not by dissolution of the egg case, but by its sudden rupture (Davis, 1981). Ultrastructural studies on the egg case of an estuarine crab Sesarma haematocheir indicated that no morphological changes occur in the thick outer layers (E1+E2; 1.5·μm in total) upon hatching. Only the innermost thin layer (E3; 0.2·μm) is markedly digested (Saigusa and Terajima, 2000). At least two kinds of active factors are contained in the hatch water (i.e. the filtered medium in which zoea larvae are released by the female), caseinolytic proteases and OHSS (ovigerous-hair stripping substance) (Saigusa, 1996). OHSS plays a role in the stripping of the embryo attachment system from the maternal ovigerous hairs just after hatching, in preparation for the next clutch of embryos (Saigusa, 1995). OHSS is clearly secreted by the embryo and not by the female (Saigusa, 1995). However, physiological mechanisms by which the stripping of ovigerous hairs is caused by OHSS are not known. Embryos of a number of animals, including the sea urchin Paracentrotus lividus (Lepage and Gache, 1990), the ascidian Ciona intestinalis (D’Aniello et al., 1997), teleosteans Oryzias latipes (Yamagami, 1988) and Hippoglossus hippoglossus The Journal of Experimental Biology 207, 621-632 Published by The Company of Biologists 2004 doi:10.1242/jeb.00785