Hatching of Mysidium columbiae was studied at Port Royal, Jamaica. Eggs in the brood pouch of the mother lose two egg membranes. Loss of the second egg membrane results in formation of a nauplius, with three pairs of free appendages. Continued development results in larvae that
bear free thoracic legs, as in the adult, but are incapable of extensive movements, and in which the eyes point dorsally instead of laterally. Ecdysis is associated with liberation of the young mysids from the brood pouch. It is estimated that from 48 to 72 hours pass between oviposition and
shedding of the second egg membrane, 48 hours between appearance of the free nauplius and shedding of the naupliar membrane, and another 48 hours between shedding of the naupliar membrane and emergence from the brood pouch. The stages in development are figured and described.
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