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THE FUNCTIONAL ANATOMY OF THE REPRODUCTIVE SYSTEMS OF THE POLYCHAETES CLYMENELLA TO RQUATA AND CAESICIRRUS NEGLECTUS

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Abstract

The reproductive systems and reproductive processes of the maldanids Clymenella torquata (Leidy) and Caesicirrus neglectus Arwidsson are described and compared. The sexes show no differences in external features, though investigations suggest that males are smaller than females of the same age. The sex ratio in Clymenella is 1:1 and both sexes become mature in their first year. The average ratio in Caesicirrus, calculated over four seasons, is 1 male: 4–2 females, and the worms do not mature earlier than their second year.

The gonads lie round the blood vessels associated with tho nephridia, in the anterior region of the trunk. Immature gametes are shed into the coelom where they undergo the early stages of gametogenesis, and become primary gametocytes. The breeding season is restricted to one or two days, immediately following a spring tide, in mid-May in Clymenella, and in late July in Caesicirrus. The nephridia act as gonoclucts. At this time, the primary oocytes are extruded into the tube, in which confined space they complete certain processes which render them fertilizable. These involve a marked reduction in diameter (of about one-third), a change in shape from flat to spherical, and the extrusion of a substance, a process which seems t o be necessary before normal cleavage can occur. The sperm of Clymenella are formed in the coelom and are free when shed, but in Caesicirrus discs of primary spermatocytes are shed, and these complete maturation in the confines of the tube after about seven hours. Both eggs and sperm are extruded at the mouth of the tube just before, or during low tide.

An attempt is made to relate the difficulties of effecting successful artificial fertilization in these and other polychaetes to the exudation of material From the oocyte while it is still in the tube.

The occurrence of hermaphrodite Caesicirrus at Whitstable is described.

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