GEMMULES OF SPONGES FROM A WARM LAKE

1. Two types of gemmules were found, each in a different species of sp onge, from the warm monomictic Lake Kinneret: (i) clustered gemmules, sharing the pneumatic layer of the gemmular capsule and resembling gem mules of Eunapius; (ii) gemmules that develop non-synchronously, conta ining amphidisc spicules within the gemmular capsule and resembling th ose of Ephydatin. Algal cells were not detected within either type of gemmule although they exist in the developed sponges. 2. Sponges began producing gemmules in the lake with the onset of lake drawdown and ce ased when lake level was minimal. The gemmules hatched when the lake l evel began to rise. 3. Under experimental conditions gemmules hatched between 13 and 35 degrees C. Germination was optimal at 20-25 degrees C. Chilling of young gemmules prior to incubation at 25 degrees C impr oved germination rate. 4. The percentage of germinating dry gemmules d iminished 4-6 months after their collection from the lake. None germin ated after 10 months. Submerged gemmules maintained high viability wit h ageing (up to 100% germination 18 months after collection). Desiccat ion influenced gemmule viability over time, by both decreasing the per centage of germinating gemmules and increasing the lag time before ons et of germination. 5. Gemmules kept in the dark germinated significant ly less than those illuminated for 12 h day(-1).