Topic
Scolecida
About: Scolecida is a research topic. Over the lifetime, 2 publications have been published within this topic receiving 158 citations.
Papers
More filters
••
TL;DR: The results support the assumption that on the basis of a broader taxon sampling the phylogenetic position of controversially discussed taxa can be inferred by using 18S rDNA sequence data.
142 citations
••
TL;DR: The development and morphology of the pigmented eyes of S. armiger suggest that they represent miniaturized eyes of the phyllodocidan type of adult eye rather than persisting larval eyes resulting in small inverse eyes typical of Scolecida, and a closer relationship of Orbiniidae to PhyllodOCida is indicated.
Abstract: The phylogenetic position of Orbiniidae within Annelida is unresolved. Conflicting hypotheses place them either in a basal taxon Scolecida, close to Spionida, or in a basal position in Aciculata. Because Aciculata have a specific type of eye, the photoreceptive organs in the orbiniid Scoloplos armiger were investigated to test these phylogenetic hypotheses. Two different types of prostomial photoreceptor-like sense organs were found in juveniles and one additional in subadults. In juveniles there are four ciliary photoreceptor-like phaosomes with unbranched cilia and two pigmented eyes. The paired pigmented eyes lie beside the brain above the circumoesophageal connectives. Each consists of one pigmented cell, one unpigmented supportive cell and three everse rhabdomeric sensory cells with vestigial cilia. During development the number of phaosomes increases considerably and numerous unpigmented sense organs appear consisting of one rhabdomeric photoreceptor cell and one supportive cell. The development and morphology of the pigmented eyes of S. armiger suggest that they represent miniaturized eyes of the phyllodocidan type of adult eye rather than persisting larval eyes resulting in small inverse eyes typical of Scolecida. Moreover, the structure of the brain indicates a loss of the palps. Hence, a closer relationship of Orbiniidae to Phyllodocida is indicated. Due to a still extensive lack of ultrastructural data among polychaetes this conclusion cannot be corroborated by considering the structure of the unpigmented ciliary and rhabdomeric photoreceptor-like sense organs. J. Morphol., 2009. © 2009 Wiley-Liss, Inc.
20 citations