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The external morphology of the spermatozoa of Hydroides elegans, H. ezoensis and H. fusicola, common species on the coast of Nagasaki City, was observed using a scanning electron microscope. The head of the spermatozoon of H. elegans consists of a conical acrosome and a pear-shaped nucleus; in H. ezoensis and H. fusicola, it consists of a beret-like acrosome and a globular nucleus, though appreciable differences in size and shape of the acrosome were found between the two species. The middle-piece consists of four globular mitochondria in the three species.
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Matsuo et al. (1983) studied this question.
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