Morphological differences between subitaneous and diapause eggs of Boeckella triarticulata (Copepoda : Calanoida)

1. Many calanoid copepods produce subitaneous eggs that hatch immediately a nd diapause eggs that remain dormant for long periods of time. Boeckella tr iarticulata (Copepoda: Calanoida) produces diapause eggs that hatch asynchr onously over an extended period of time and appear identical under light mi croscopy to those that hatch immediately. 2. We compared the internal morphology of subitaneous and diapause eggs of B. triarticulata that had been prepared for transmission electron microscop y by four methods. 3. Subitaneous eggs had a thin, single-layered shell whe reas diapause eggs had a thick, three-layered shell that appeared consisten t over 3 months of diapause. Boeckella triarticulata appears to enter diapause at the multicellular stage. 4. Consistent morphological differences between subitaneous and diapause eg gs of B. triarticulata suggest that these two egg types also have distinct differences in physiology, and are not merely extremes of a continuum from subitaneous to diapause eggs.