CRYOPRESERVATION OF NEREIS-VIRENS (POLYCHAETA, ANNELIDA) LARVAE - THEMECHANISM OF CRYOPRESERVATION OF A DIFFERENTIATED METAZOAN

The volumetric changes, structural behavior, and subsequent survival r ate of juvenile Nereis (Neanthes) virens (Annelida: Polychaeta) at the three chaetiger stage of development have been observed during equili brium and nonequilibrium low-temperature dehydration in a controlled-r ate freezer and on the stage of a planar cryomicroscope. Using a cooli ng rate 0.3 degrees C/min and 1.4 M Me2SO, substantial levels of larva l survival were observed following transfer to liquid N from a tempera ture of -25 degrees C when the equilibrium fractional water volume is expected to be 7.1%. The cryopreservation under equilibrium conditions is thought to indicate vitrification of the internal Me2SO which will have reached 54% at -25 degrees C. When a cooling rate of 2.5 degrees C/min was used, the long-term survival rate was substantially greater , reaching 86%, depending on developmental stage following transfer to liquid N from a temperature of -35 degrees C. (C) 1997 Academic Press .