A CONTRIBUTION TO THE BIOLOGY OF A DEEP SEA ECHINOID, ALLOCENTROTUS FRAGILIS (JACKSON)

¹ Hopkins Marine Station of Stanford University, California

1. Following a chance collection of a deep sea urchin, Allocentrotus fragilis, from a depth of 80 fathoms, it subsequently became possible to collect the urchins on numerous occasions from the same area.

2. The area of the bed was determined by grid dredging and the nature of the habitat determined to be relatively flat, gravel and sand underlaid with gray silt containing organic detritus and microscopic organisms.

3. The deep sea urchin appears to graze on the bottom since the organisms and organic debris of the bottom sediment appear in little pellets in its gut.

4. Many types of invertebrates are associated with Allocentrotus, including various other echinoderms. A variety of fishes is found as well.

5. Individuals with mature gametes were obtained in February and March of 1957 and during the period of September, 1957 to January, 1958. Spawn-out appeared to occur between February and March during both years.

6. Attempts to correlate the life cycle of Allocentrotus with various environmental factors led to the suggestion that upwelling may trigger spawning. The planktonic larvae then presumably develop during the most effective time when the planktonic blooms occur.