Morphology and growth of the larval stages of Geograpsus lividus (Crustacea, Brachyura), with the descriptions of new larval characters for the Grapsidae and an undescribed setation pattern in extended developments

Among the eight currently recognized genera and 40 species belonging to the brachyuran crab family Grapsidae (Thoracotremata), the complete larval development is only known for three species of Metopograpsus. In this study, we investigated the larval development of Geograpsus lividus originating from Jamaica and reared under controlled conditions in the laboratory. It consists of eight zoeal stages and the megalopa, representing the longest recorded developmental pathway for any brachyuran. Although long developments had been suggested for some species, based on specimens collected from the plankton, these were never confirmed by laboratory culture. In this study, zoeal growth (measured as increase in body size, dry mass, and contents of carbon, nitrogen, and hydrogen) is quantified, and morphological and meristic characters of the larval stages of G. lividus are described and illustrated. The development from hatching to the end of the zoeal phase took 2 months. During this time span, larval size (cephalothorax length) increased 4.4-fold, while the various measures of biomass increased by factors of 57-72. Morphologically, the larvae present most characters previously established for the family Grapsidae. However, the two last zoeal stages show new features that differ from the typical setation pattern known from grapsid species with only five zoeal stages. These were found in the number of natatory setae on the exopods of the maxillipeds and in the setation of the basis of the first maxilliped. Other characters, which had previously only been described for zoeae of Pachygrapsus and plankton-collected ones attributed to Planes, were observed also in G. lividus and could be confirmed as common features for the Grapsidae. Moreover, the larvae of G. lividus present a spinulation on the lateral and rostral spines of the cephalothorax. This character is recorded for the first time in grapsid crabs. A comparison of these observations is made with those based on terminal zoeal stages of species belonging to other brachyuran families, where similar characters have been documented.