Effects of cryopreservation on the ultrastructural anatomy of 3-segment Nereis virens larvae (Polychaeta)

A transmission electron microscope study of fresh and cryopreserved Nereis virens larvae at the three chaetiger stage is described with special emphas is on examining the structure of the photoreceptors and surface ciliation o f the head, the midgut epithelium, and muscle cells. Complex ectodermal str uctures such as the developing rhabdomeric adult eyes were unaffected by th e cryopreservation procedure. Some loss of surface cilia on the prostomium was observed but is not life-threatening though it may restrict ciliary swi mming in the recovered larvae. Loss of pigment from the prostomium is cause d by osmotic stress. Structural damage was observed in the digestive tissue s of the larvae cryopreserved before or after the optimum stage of developm ent. This damage is potentially more serious and may account for the relati vely short time period during development where cryopreservation can be suc cessfully applied.