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Title: On the Biology of Sexual Reproduction of Hydromedusae, Genus Phialidium Leuckhart 
Author: Roosen-Runge, Edward C.
Date: 1962-01
Publisher: University of Hawai'i Press
Citation: Roosen-Runge EC. 1962. On the biology of sexual reproduction of hydromedusae, genus Phialidium Leuckhart. Pac Sci 16(1): 15-24.
Abstract: The genus Phialidium is nearly ubiquitous in
the coastal waters of the temperate zone. The
medusae occur at Friday Harbor certainly from
April through September and disappear rather
suddenly in October, under circumstances which
need investigation. Drifting with tides and
currents, they occur in swarms which greatly
vary in density. During the present investigation
no swarms were seen in which individuals,
on the average, were closer to each other than
a few inches; usually they were many inches to
several feet apart. Under these circumstances it
would seem that fertilization becomes somewhat
of a problem. In a population which, as a
whole, is moving passively, and in which individuals
appear to have no affinity to each
other, ovulation and spermiation must be closely
and appropriately timed and the properties of
eggs and sperms evolved to insure a high rate
of fertility, the results of which are seen in the
wide distribution and in the tremendous numbers
of colonies of the sessile stages of the
species, the hydroid polyps. The present paper
attempts to clarify some of the factors which
insure the high reproductive capacity of hydromedusae
under what, on first sight, appear to
be difficult circumstances.
ISSN: 0030-8870

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