Abstract

External morphological changes in embryos of the hair crab Erimacrus isenbeckii (Brandt) reared in the laboratory were observed. Embryonic development was divided into 9 stages based on morphological changes: precleavage stage, cleavage and blastula stage, gastrula stage, naupliar stage, metanaupliar stage, pigmented-eye stage, heartbeat-initiation stage, prezoea stage, and prehatching stage. Embryos spawned by a female in January developed to the gastrula stage by March. Embryos from another female developed from the gastrula stage to the prehatching stage from March to December, and hatched in January. These results suggest that the incubation period under laboratory conditions was about 12 months. Since one female collected in February still carried prezoea-stage embryos, the embryonic growth rate in the laboratory was expected to be higher than in the field. It is thought that the length of the incubation period is affected by many environmental factors, but the embryonic growth rate is mainly controlled by water temperature. Thus, around Hokkaido, where specimens studied were collected, incubating females may be distributed in temperatures cooler than in the laboratory.