Embryonic development of the oligochaeteEnchytraeus coronatus: An SEM and histological study of embryogenesis from one‐cell stage to hatching

Abstract

We describe the embryonic development of the soil-living oligochaete Enchytraeus coronatus (Enchytraeidae, Oligochaeta, Annelida). Enchytraeus coronatus is a direct developer. It follows the typical spiral cleavage mode of development that is highly conserved among annelids and a large number of other lophotrochozoan taxa that are collectively named "Spiralia." Scanning electron microscopy (SEM) was combined with light microscopic analysis of wholemounted and sectioned embryos, differentially processed through histological stainings, to reconstruct and document cellular movements and organogenesis from early cleavage stages until hatching. With the help of these data we have established a scheme of morphologically defined stages in order to facilitate future studies on the molecular and histological level that will allow a detailed cross-species comparison among annelids and other phyla.

Development and embryonic pattern of body wall musculature in the crassiclitellate Eisenia andrei (Annelida, Clitellata)

“…In this study we have examined the differentiation of the somatic muscles during embryogenesis of the crassiclitellate Eisenia andrei in order to compare our findings with the muscle pattern formation during development in the clitellates Limnodrilus sp. (Naididae), Enchytraeus coronatus (Enchytraidae), and Erpobdella octoculata (Hirudinea, Erpobdelliformes) studied previously (Bergter et al, 2004. Until now, these findings imply, that muscle development in Clitellata widely depends on the life style of the species.…”

Pattern of body‐wall muscle differentiation during embryonic development of Enchytraeus coronatus (Annelida: Oligochaeta; Enchytraeidae)

“…The terrestrial oligochaete Enchytraeus coronatus develops within a cocoon, which is secreted by the cells of the clitellum, and follows the spiral cleavage pattern with an initial unequal cleavage (Bergter et al, 2004). As is common for directly developing oligochaetes, the ectoderm is formed by the teloblastic cleavage of a bilateral pair of four ectoteloblasts (N,O,P,Q left and right, respectively), all descendants of the 2d-cell.…”

“…Cells of one m-blast cell clone are older and therefore further in the process of development than the ones in the following posterior segment. Since early cleavage pattern as well as formation of a germband of teloblastic origin in Enchytraeus coronatus strikingly resembles that of those clitellates (Bergter et al, 2004), it can be assumed that descendants of m-blast cells contribute to mesodermal tissue in a similar, if not entirely the same, segmental manner. However, our findings indicate that muscle differentiation in E. coronatus differs from the previously described pattern of segmentally emerging muscle blocks during annelid embryogenesis (Anderson, 1973).…”

“…In the present work we examined muscle differentiation during embryogenesis of Enchytraeus coronatus, a directly developing oligochaete (Bergter et al, 2004;Erséus and Källersjö, 2004), providing the first data on pattern formation during myogenesis for an oligochaete.…”

Annelids in evolutionary developmental biology and comparative genomics

“…2D) 1999), a reproductive process has evolved which involves the clitellum and the formation of a cocoon in which the embryos are nourished on a supply of yolk and have done away with the requirement for a feeding trochophore larva. Further to this, development via large teloblast cells is employed by the leech and oligochaetes (Weisblat & Huang, 2001;Bergter et al, 2004), and the evolutionary relationship between these leech teloblasts and cells in the posterior growth zone of polychaetes is an important issue to be resolved (de Rosa et al, 2005;Shimizu & Nakamoto, 2001;Seaver et al, 2005). The discussions on the reconstruction of the annelid and clitellate ancestors have been reviewed in greater detail elsewhere (e.g.…”