The Spermatozoon of Actinia Equina L. Var. Mesembryanthemum

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Abstract
The spermatozoon of A. equina var. mesembryanthemum is of the primitive type, although lacking a well-defined acrosome. The sperm nucleus is cyclindrical, .apprx. 1.25 .mu.m long and 1 .mu.m in diameter. The posterior surface of the nucleus is indented to form a shallow nuclear fossa in which lies the proximal centriole, which is inclined at an angle of approximately 45.degree. to the long axis of the sperm. The distal centriole, which gives rise to the tail flagellum, is surrounded by a ring of 9 pericentriolar processes. The anterior region of the tail is surrounded by a cytoplasmic collar, against which terminate projections from the pericentriolar processes. The midpiece of the sperm contains a single, large mitochondrial complex, positioned asymmetrically and which is associated with a single lipid-like droplet. Numbers of clear, cored and dense vesicles are found in the midpiece, some of which resemble the donut or pro-acrosomal vesicles of other species. A dense, membrane-bound body with a characteristically angular electron-lucent core of varying size and shape is also found, usually alongside the basal region of the nucleus. Its function is unknown, but it resembles the residual body-like inclusions seen in gastrodermal cells. The sexual reproduction of A. equina is imperfectly understood and appears unusual in several respects. The spermatozoon appears normal and comparable to other anthozoan sperm so far examined.