The functional morphology and possible taxonomic significance of the parapodia of the maldanid polychaetes Clymenella torquata and Euclymene oerstedi

Abstract

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.

Significance of chaetal arrangement for maldanid systematics (Annelida, Maldanidae)

“…The histological data of Euclymene oerstedii revealed that the rows of chaetae in anterior chaetigers form anteroposterior rows at the level of the bases and thus are twisted on their course up to the body surface. These findings are congruent with those of Pilgrim (1977). In posterior notopodia of Euclymene oerstedii the chaetae are instead arranged in the form of a fan in a single plane and the bases are aligned in the same anterorposterior direction as the upper parts of the chaetae.…”

“…In contrast to this the notopodia have rows of different types of capillary chaetae. Pilgrim (1977) described a shift of the notopodial chaetal rows from a transverse direction (seen in relation to the body axis) in anterior chaetigers to a more longitudinal one in posterior chaetigers in Clymene torquata and Euclymene oerstedii, both belonging to the Euclymeninae. This shift is not typical for sedentary polychaetes.…”

Phylogenetic significance of chaetal arrangement and chaetogenesis in Maldanidae (Annelida)

“…Each transverse double row consists of longer anterior and shorter posterior chaeta, an observation already mentioned by Arwidsson (1906). In all species of Euclymeninae, however, the double row of notochaetae is parallel to the antero-posterior body axis from chaetiger 13 onward in the posterior segments; stepwise transition between both conditions can always be seen in chaetiger 11 and 12 (De Assis and Christoffersen 2011; Hausen and Bleidorn 2006;Pilgrim 1977).…”

“…The correlation between chaetal sac structure and position of the notopodial double row is indirectly supported by older studies. Given that chaetae are continuously replaced (Pilgrim 1977), new chaetae will be added to the posterior margin of each notopodium in posterior segments of euclymenin species, but to the ventral margin of the notopodia in the remaining maldanid species. When seen from the exterior, new chaetae can easily be recognized by their shortness (Hausen 2005).…”

“…After being formed on one end of the row, the chaetae appear on the surface, come into function, become worn out and finally degenerate at the opposite end of the row. Rows of hooked chaetae are therefore flanked by a formative side and a site of chaetolysis (Pilgrim 1977;Hausen 2005). The formative site generally contains several developing chaetae, making them an ideal subject to study chaetogenesis.…”