Back to Search
Start Over
Nervous and muscle system development in Phascolion strombus (Sipuncula).
- Source :
-
Development genes and evolution [Dev Genes Evol] 2005 Oct; Vol. 215 (10), pp. 509-18. Date of Electronic Publication: 2005 Nov 01. - Publication Year :
- 2005
-
Abstract
- Recent interpretations of developmental gene expression patterns propose that the last common metazoan ancestor was segmented, although most animal phyla show no obvious signs of segmentation. Developmental studies of non-model system trochozoan taxa may shed light on this hypothesis by assessing possible cryptic segmentation patterns. In this paper, we present the first immunocytochemical data on the ontogeny of the nervous system and the musculature in the sipunculan Phascolion strombus. Myogenesis of the first anlagen of the body wall ring muscles occurs synchronously and not subsequently from anterior to posterior as in segmented spiralian taxa (i.e. annelids). The number of ring muscles remains constant during the initial stages of body axis elongation. In the anterior-posteriorly elongated larva, newly formed ring muscles originate along the entire body axis between existing myocytes, indicating that repeated muscle bands do not form from a posterior growth zone. During neurogenesis, the Phascolion larva expresses a non-metameric, paired, ventral nerve cord that fuses in the mid-body region in the late-stage elongated larva. Contrary to other trochozoans, Phascolion lacks any larval serotonergic structures. However, two to three FMRFamide-positive cells are found in the apical organ. In addition, late larvae show commissure-like neurones interconnecting the two ventral nerve cords, while early juveniles exhibit a third, medially placed FMRFamidergic ventral nerve. Although we did not find any indications for cryptic segmentation, certain neuro-developmental traits in Phascolion resemble the conditions found in polychaetes (including echiurans) and myzostomids and support a close relationship of Sipuncula and Annelida.
- Subjects :
- Animals
Embryo, Nonmammalian embryology
Immunohistochemistry
Larva growth & development
Microscopy, Confocal
Microscopy, Electron, Scanning
Muscle Development physiology
Nematoda growth & development
Nematoda ultrastructure
Nervous System growth & development
Queensland
Species Specificity
Sweden
Body Patterning physiology
Muscles embryology
Nematoda embryology
Nervous System embryology
Subjects
Details
- Language :
- English
- ISSN :
- 0949-944X
- Volume :
- 215
- Issue :
- 10
- Database :
- MEDLINE
- Journal :
- Development genes and evolution
- Publication Type :
- Academic Journal
- Accession number :
- 16133569
- Full Text :
- https://doi.org/10.1007/s00427-005-0012-0