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

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.

The anatomy and histology of the blood system of the maldanid polychaetes Clymenella torquata and Euclymene oerstedi

“…The evidence that most of the posterior regenerations occurring in these maldanids are the result of spontaneous autotomies, and not accidents, is persuasive, and is outlined briefly below. More detailed information is recorded elsewhere (Pilgrim, 1960;Sayles, 1932Sayles, , 1934Sayles, ,1936Sayles, and 1943. (i) The body wall at each intersegmental boundary, with the exception of the posterior boundaries of the head and of the last true segment in both species, and also of the penultimate segment in Euclymene, shows a specialized structure which would ensure breakage at these levels only, under any condition of longitudinal strain, such as could easily be exerted by the worm itself within its tube, or as a result of a powerful constriction in the vicinity (see below).…”

“…In Clymenella, gamete formation never stops completely, even in winter. In Euclymene, very few, if any, gametes seem to be formed from November to January (Pilgrim, 1964). During this period, many disintegrating oocytes and sperm discs are found in the coelom and are ingested by the coelomocytes.…”

“…In male Clymenella, the spermatozoa are released in the coelom, and masses of blastophores (the residual cytoplasm of the sperm discs) are thereby released. In Euclymene, whole spermatocyte discs are discharged from the body to complete their maturation in the tube (Pilgrim, 1964), and consequently any blastophores which appear in the coelom are those released from disintegrating discs. In both species, at the close of breeding, blastophores, young discs, bits of old discs and even whole old discs are ingested by the coelomocytes.…”

Capitellid connections: contributions from neuromuscular development of the maldanid polychaete Axiothella rubrocincta (Annelida)

“…Most studies of the internal morphology of maldanid polychaetes have focused on members of the subfamily Euclymeninae [ 13 ], to which also the investigated species, Axiothella rubrocincta , belongs. In particular, the comprehensive investigations of Pilgrim [ 16 - 21 ] serve thereby as a basis for comparison of our data on neuro- and myogenesis. We discuss the present data in the context of a hypothesized close annelid-echiuran relationship and contribute to the discussion on ancestral bodyplan features of the Annelida.…”