JUVENILE MORPHOLOGY AND APPEARANCE OF SEXUAL APPENDAGES IN 2 PORCELLANID CRABS, PETROLISTHES-RUFESCENS (HELLER, 1861) AND PISIDIA-GORDONI (JOHNSON, 1970) (DECAPODA, ANOMURA, PORCELLANIDAE)

Abstract

The porcellanid crabs in their larval phase show typical anomuran features but develop a crab-like form from megalopa through the juvenile instars. However, the adult species characters are not yet noticeable in the juvenile phase thus leading to confusion in identity both at specific or even at generic level. With attainment of the crab-like form, the reproductive appendages, like male pleopods, show a brachyuran pattern. In absence of external sexual dimorphism, sex determination is difficult in this group. Very little information is available as to how and when the sexual appendages start developing in Porcellanidae. With the purpose of tracing the development of the adult taxonomic characters and that of the reproductive appendages (and sex differentiation), the present paper describes the juvenile laboratory development of two porcellanid crabs, viz. Petrolisthes rufescens (Heller) up to instar III and Pisidia gordoni (Johnson) up to instar IV. Taxonomic features: In both the species the definitive adult features like those of the carapace front and its armature, the chelipeds and other pereiopods, the sternite of the third maxillipeds, etc., develop in the third instar. Sexual appendages: (a) In Petrolisthes rufescens the primary pleopods get totally reduced at least up to instar III and, therefore, the sexual appendages appear to be developing as a secondary series of pleopods, particularly in the female. (b) In Pisidia gordoni, at least in the male, differentiation starts from instar II onwards with the first pleopod modifying into a male appendage, while the remaining pleopods gradually become reduced.