A comparative study of morphology and ontogeny in juvenile stages of four Western Atlantic xanthoid crabs (Crustacea: Decapoda: Brachyura)

Abstract

Four species ofxanthoid crabs of the family Panopeidae ( sensu Guinot 1978) ( Panopeus bermudensis, P. herbstii forma simpsoni, P. turgidus , and Eurypanopeus depressus ) were reared in the laboratory from eggs to the fifth crab instar. The fourth (last) zoeal stage and megalopa are described for P. bermudensis and P. turgidus . The carapaces of the first, second, third and fifth crab stages are described for all four species; mouthparts and fifth pereopods are described for selected stages of all four species. The zoea of P. bermudensis is a modified member (lacking lateral carapacial spines) of Rice’s group I xanthid zoeas (Rice, A. L., 1980 Trans. Zool. Soc. Lond . 35, 271-424) and is markedly different from the zoeas of the other three species. The zoea of P. turgidus is very similar to the zoea of P. herbstii , although the megalopa of P. turgidus resembles that of E. depressus . Carapaces of early crab stages were similar in all four species. Differences in carapace morphology and mouthpart setation were more evident in the fifth crab stage than in the first and third crab stages. A discriminant analysis based upon setation of selected mouthparts and spination of the fifth pereopod dactyl was used to demonstrate quantitatively ontogenetic divergence in phena of the four species. Results of this analysis reflect the minimum expression of adult specializations in the early crab stages, a quality that may justify use of these conservative stages in the ellucidation of lineages of brachyuran groups.