STUDIES ON THE LIFE HISTORY OF THE MARINE ANNELID NEREIS VEXILLOSA

¹ Scripps Institution of Oceanography, University of California, La Jolla, and the University of Washington Oceanographic Laboratories, Seattle

Nereis vexillosa deposits its eggs in firm irregular gelatinoid masses which vary in size from about one to three inches in diameter.

Spawning of small (6 to 8 cm. long) heteronereids of this species was observed to take place an hour or two before midnight. The eggs which are demersal are apparently spawned in water at or just beyond the extreme low tide level and this habit may account for the finding of fewer egg masses than seems commensurate with the number of the species producing them. Isolated heteronereis females were induced to discharge their eggs by the introduction of spermatozoa into the water.

Worms cultured in the laboratory from egg masses collected on the beach throve best on fresh animal food. A number of young worms transported from Friday Harbor to La Jolla attained a maximum length of 10 cm. at the age of 13 months after hatching. All had acquired specific characteristics but none became heteronereized. The transformations taking place during cephalization are similar to that occurring in other nereid worms.

Since the above maximum size of the reared worms is comparable to that of the small spawning heteronereis forms, it appears that the latter were spawning at the age of about one year. Much larger nereis and also heteronereis individuals are known to occur in this species but the time and steps involved in their development are unknown.