The morphology of the head, thorax, proboscis apparatus and pygidium of the maldanid polychaetes Clymenella torquata and Euclymene oerstedi

Abstract

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.

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

“…In the case of adult individuals of Axiothella rubrocinta , the number of longitudinal strands is not known. However, the closely related maldanid species Clymenella torquata has been depicted by illustrations of cross sections with up to six longitudinal bands that form an almost closed muscle layer [ 19 ]. In larval stages of Axiothella , only four delicate longitudinal muscles form the precursors of the later paired ventral and dorsal longitudinal muscle bands.…”

“…In this respect, it has to be taken into account that A. rubrocincta represents a sibling species complex with considerable plasticity between populations concerning reproductive mode, size, and feeding, but with no obvious morphological differences [ 22 ]. Herein, we have adopted most of Pilgrim's [ 19 - 21 ] designations. However, we use different terms for some neuronal structures and the anterior-most muscles in the head region due to incongruency of the macro-anatomical data described by Pilgrim, which are based on light microscopy, and our confocal microscopy data.…”

Phylogenetic relationships within Maldanidae (Capitellida, Annelida), based on morphological characters

“…2). The thorax is formed by the first three chaetigers, in which the circular muscles are relatively thicker than the longitudinal muscles (Pilgrim, 1966). Parapodia are biramous, with cylindrical, truncate notopodia, bearing tufts of notochaetae, while anterior neuropodia have acicular spines or rostrate uncini (Day, 1967;Imajima & Shiraki, 1982a;De Assis et al, 2007a) (Fig.…”