The morphology of the chaetae of the maldanid polychaetes Clymenella torquata (Leidy) and Euclymene oerstedi (Claparède) (= Caesicirrus neglectus Arwidsson, '11) are described and related to movements observed in the laboratory. Graphs are constructed of the number and length of the neuropodial chaetae of each chaetiger throughout the body of Clymenella and of species of the genera Euclymene, Macroclymene and Axiothella, and show a characteristic and relatively constant pattern for each species. This work suggests that in making taxonomic decisions, more attention should be paid to the overall pattern of the neuropodial chaetae and less to the confusing distinction between aciculae and rostral uncini.
The nervous system of the maldanid polychaetes Clymenella torquata (Leidy) and Euclymene oerstedi (Claparede) (= Caesicirrus neglectus [Arwidsson, '11‐'12]) retains its primitive association with the epidermis. It shows only slight metamerism in the presence of larger collections of neurones opposite the parapodia and of larger nerves at the segmental boundaries. Multicellular giant fibers are present in the ventral nerve cord; giant neurones which show a characteristic pattern of distribution in each species are also present. The cerebral ganglia supply nerves to the prostomial wall, nuchal grooves and the wall of the buccal cavity, and a pair of large nerves from the circumpharyngeal connectives also appear to join the buccal system. The organs of special sense are the elongated prostomial nuchal grooves, and prostomial ocelli in Euclymene but not in Clymenella. Statocysts are absent. Four pairs of nephromixia are present. They lie in the aseptate anterior trunk, in chaetigers 5–9 of Clymenella, and 6–10 of Euclymene. The nephridiopores lie at the ventral ends of the neuropodia of chaetigers 6–9 and 7–10, respectively. Each nephromixium consists of coelomostome, tubule and contractile bladder. The wall of the tubule and bladder consists of both excretory and ciliated cells. Most of the cytoplasm of the latter forms a bounding layer at the outer surface. The cytoplasm of the excretory cells contains lipid material and appears to synthesize lipofuscin. The tips of the excretory cells swell, fill with granules, and break off in the form of vesicles which are periodically expelled in clouds from the nephridiopores. Glycogen is present, especially in the ciliated cells of the tubule and coelomostome. Granules of a lipoid nature accumulate in (or between) cells of the nephridia, epidermis, and some regions of the gut, and may be excretory. Lipid granules also appear to be synthesized by coelomocytes which eventually end up in masses in the ventrolateral coelomic cavities of the tail. The nephridia act as gonoducts, but show no seasonal variation in either size or histological structure.
The alimentary canal of the maldanid polychaetes Clymenella torquata (Leidy), and Euclymene oerstedi (Claparède (=Caesicirrus neglectus Arwidsson, 1911) resembles, in many ways, that of the arenicolids. It is divided into buccal mass, pharynx, oesophagus, stomach and intestine, the three latter regions showing further subdivision. The buccal mass and anterior pharynx together form an eversible proboscis. The pharynx, oesophagus, and greater part of the intestine are ciliated. Simple feeding experiments, and histochemical tests, suggest that the stomach is concerned with the digestion and absorption of proteins, fats and carbohydrates, that the anterior intestine is a digestive and major absorptive region, and that the posterior intestine is a storage region. Waste materials are stored mainly in the wall of the oesophagus. A certain amount of intracellular digestion is carried out in the intestine of Euclymene but not in Clymenella. The difference is attributed to the richer, diatomaceous diet of Clymenella. British individuals of this species, being apparently selective feeders, differ not only from Euclymene but also from American ones, both of which ingest the substratum non‐selectively. The pharynx, oesophagus and rectum are surrounded by plexuses of blood capillaries, while the remaining regions are associated with a blood sinus system which varies in position and form in the different regions, lying deepest in the absorptive intestine. The gut muscle seems to be more concerned with moving the blood forward through the sinus system and into the anterior plexus than with moving the food backward. One region of the stomach musculature is especially concerned with this circulation. Rectal respiration probably occurs.
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.
A detailed description is given of the anatomy of the head, thorax, proboscis apparatus and pygidium of the maldanid polychaetes Clymenella torquata (Leidy) and Euclymene oerstedi (Claparède) (=Caesicirrus neglectus Arwidsson, 1911). The head consists of prostomium, peristomial region and one achaetous segment which is undoubtedly a metamere. Whether the peristomium should be counted as another rests on the definition of a metamere, about which opinions differ. Evidence is presented which suggests that each of the two paired groups of proboscideal retractors is derived from a head septum. Probably because of the relatively large size of the proboscis, not only the head, but also the first four chaetigers (= thorax) act as a pump to effect the eversion of the proboscis by coelomic fluid pressure. The thoracic septa are highly specialized in relation to this function. In both gross and detailed anatomy, and in mode of functioning of the region, the maldanids show many resemblances to some arenicolids. The pygidium consists of a ring‐shaped thickening (the callus ring), the anal funnel and the anal cone. Based on this investigation of anatomy, a system of description is suggested which aims to avoid ambiguity and to eliminate from future maldanid literature the type of confusion which exists in it at present.
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