Figure 1

Morphological changes associated with preparation for diapause or preparation for the terminal molt in Calanus finmarchicus. As copepodids progress through the C5 stage toward the terminal molt, the mandibular cuticle separates from the epidermis (apolysis), the gonad develops (grows and changes cell structure) and differentiates (allowing gender to be identified), and the oil sac increases to a moderate size. As copepods progress toward diapause, the oil sac increases to a very large size, but molt stage progression (measured by jaw phase) and gonadal development are arrested.