Embryonic development and morphometry in the blue king crab, Paralithodes platypus, studied by image and cluster analysis

In this paper the embryonic development of laboratory-reared blue king crab, Paralithodes platypus, from the Pribilof Islands in the eastern Bering Sea is described. Developing embryos were removed from a female crab at various intervals, digitally photographed under a compound microscope and analyzed using Image-Pro Plus. Nine morphometric parameters were used, including seven measurements (total area, yolk area, embryo length and width, average diameter, eye length and width) and two calculated indices (percent yolk and elongation). First cell division was not apparent until day 4, after which divisions occurred daily until the blastopore appeared at day 28. A "V"-shaped embryo became apparent on day 114, followed by rapid appendage development. The eyes became pigmented by day 192. Hatching occurred from day 381 to day 409, and required at least 33 d to complete. Embryo area declined from an initial value of 0.95 mm 2 on day 1–0.83 mm 2 on day 72 and then increased to 1.28 mm 2 on day 388. Growth of all characters reached a plateau between days 240 and 353, and then increased rapidly until the middle of hatching (day 390). Visual examination was better at defining early changes, but cluster analysis of morphometric measurements was a better technique for defining middle and later stages. Both techniques resulted in an optimum selection of 12 developmental stages. Embryonic develop-ment has been described for few decapod crustaceans, and no standard exists for defining developmental stages. Multivariate analysis of morphometric measurements may lead to improved understanding of crustacean embryogenesis, allow standardization of staging and enable studies of environmental influence on development. The technique also has applications in the aquaculture industry.