Redescription of megalopa and juvenile development of Pachygrapsus gracilis (Decapoda: Grapsidae) from the Amazon region, reared in the laboratory

ABSTRACT: This present study re-describes the megalopa stage and provides detailed morphological descriptions and main growth changes observed in stages I through VII of the juvenile instars of the dark shore crab Pachygrapsus gracilis (Saussure, 1858), from the Amazon region. The specimens in this study were reared in the laboratory and the megalopae were collected at Ajuruteua beach in northeastern Pará, Brazil. Previous studies had described the megalopa of P. gracilis from Mexican waters, as well as those of Pachygrapsus transversus (Gibbes, 1850) and Pachygrapsus marmoratus (Fabricius, 1787). A comparison between the Mexican and Amazonian populations of P. gracilis revealed significant morphological differences. The main difference is the presence of 3 elongated setae on the 5th pereiopods of individuals of the Amazonian population. The setal number and their arrangement in the appendages also differed. In P. gracilis, the male and female genital openings are observed from the juvenile instar III, whereas differentiation in male pleopods is observed only in juvenile instar V. In females, the pleopods undergo rapid differentiation during juvenile instar VI. These morphological comparisons and other observations on development are briefly compared and discussed with reports for other species.

Development and functional morphology of the foreguts of larvae and postlarvae of three crustacean decapods

O desenvolvimento da estrutura do estômago e da função digestiva foi examinada em larvas e pós-larvas de Litopenaeus vannamei, Sesarma rectum e Callichirus major. O estômago do protozoea de L. vannamei é muito simples, sem válvula cárdiopilórica e apresenta um filtro pilórico rudimentar. Em mysis, o filtro pilórico parece ser mais desenvolvido. No juvenil I surgem calhas e dentes laterais pouco desenvolvidos. Os estômagos dos zoeae de S. rectum possuem a válvula cárdiopilórica e o filtro pilórico funcionais. Nos estágios megalopa e juvenil I o moinho gástrico é complexo. Em C. major, os estômagos dos zoeae se mostram especializados exibindo algumas estruturas rígidas, mas não apresentam moinho gástrico. Esta estrutura surge no megalopa e juvenil I. Os resultados suportam suposições anteriores que o comportamento alimentar de larvas e pós-larvas está diretamente relacionado com as características morfológicas dos estômagos.