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Title: Annual Reproductive Cycle of Two Japanese Species of Sipunculans: Siphonosoma cumanense (Sipunculidae) and Phascolosoma scolops (Phascolosomatidae) 
Author: Catalan, Maria Antonina Batac; Yamamoto, Masamichi
Date: 1994-04
Publisher: University of Hawaii Press
Citation: Catalan MAB, Yamamoto M. 1994. Annual reproductive cycle of two Japanese species of sipunculans: Siphonosoma cumanense (Sipunculidae) and Phascolosoma scolops (Phascolosomatidae). Pac Sci 48(2): 145-157.
Abstract: The annual reproductive cycles of the Japanese sipunculans
Siphonosoma cumanense (Keferstein) and Phascolosoma scolops (Selenka, de
Man & Biilow) were studied based on size, density, and frequency distribution
of gametes from May 1989 to November 1990 and October 1989 to February
1991, respectively. Aliquots from the total volume of the diluted coelomic fluid
from each individual were analyzed. Coelomic oocytes of S. cumanense showed
a slow growth rate (i.e., 3 um/month) from December to April. An accelerated
rate was observed in May to July. No oocytes were encountered from September
to December, suggesting that spawning occurs in July to August. Sperm clusters
were encountered only from May to August, with peaks in June and July. In
contrast, oocytes and sperm clusters of P. scolops were present throughout the
year. From January to March small oocytes grew at an average rate of 10
um/month. Oocytes showed rapid growth until July. Smaller oocytes were noted
thereafter, indicating a summer spawning. Fluctuation of sperm cluster density
showed a pattern similar to that of oocytes. Both species showed two major
peaks in gamete density, one during oocyte proliferation and one before
spawning. Stages of gametogenesis in both species are described.
ISSN: 0030-8870

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