Cell proliferation and morphological patterns in the hydroidsTubulariaandHydractinia

Abstract

ABSTRACTMitotic figure distributions in the hydroids Tubularia and Hydractinia are related to both the axial and radial morphological organizations of the polyps. Cells divide in all regions of the body except at some extremities, but the abundance of dividing cells varies along the polyp axis. For example, in Hydractinia gonozooids mitotic figures are concentrated in the constricted part of the column, and in the Tubularia hydranth they are most abundant just above the whorl of gonophores. The polyps of both species of hydroids have a similar radial organization. In the distal hydranth portions this is manifested both in the positions of tentacles and in the positions of longitudinal gastrodermal ridges called taeniolae. Taeniolae generally are spaced between tentacles. In Tubularia and in Hydractinia gastrozooids, mitotic digestive cells are radially localized between taeniolae, that is, along the tentacular radii. The taeniolate organization appears to be a fundamental one in view of its wide phyletic distribution and its relation to other morphological and mitotic patterns. The similarity in mitotic patterns among different polyps is consistent with wide homologies existing between the structures of diverse hydroid types.