Developmental morphology of the optic cushion and ocelli of the sea star Leptasterias polaris (Müller & Troschel)

Emerson, Carolyn Jean (1977) Developmental morphology of the optic cushion and ocelli of the sea star Leptasterias polaris (Müller & Troschel). Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (31MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

A study of the morphology of the optic cushion and ocelli of the sea star Leptasterias polaris (Müller and Troschel) was undertaken to provide a description of their fully differentiated condition, and as a comparison with similar work on the ocelli of other species of asteroids and on the photoreceptors of other animals. In addition, the development of the optic cushion and its ocelli through embryogenesis, and the regeneration of adult tissues were investigated. For these studies, larvae of L. polaris, and the optic region of the fully formed adult, and of adult regenerating rays, were examined by light, scanning electron, and transmission electron microscopy. -- The ocelli consisted of numerous pigmented and sensory cells that lined a lumen. The designation of the sensory cells as ciliary photo-sensory receptors was confirmed by observations of the prominence and microtubular irregularities of the numerous cilia present in the lumen, and by the origin of villi from the base of their shafts, as well as from the cell membrane of the expanded apical portions of the sensory cells. The presence of coated cell membrane invaginations, coated vesicles, and multivesicular bodies, suggested a mechanism of endocytosis of villous membrane, such as has been documented as a photoreceptoral membrane recycling pathway in rhabdomeric photoreceptors. -- The pigmented cells possessed small pigment granules, and larger polymorphic bodies proposed to be stages in autophagocytosis. Corneal cells subserved a supportive function, surrounding the ocellus and projecting processes containing vesicular profiles and a microfilamentous bundle, over the lumen. -- In both larval and regenerative development, a region of epidermal cells at the base of the terminal tentacle, commenced differentiation into the three classes of ocellar cells. This region then invaginated and the corneal components extended processes over the lumen, which gradually became filled with the apices of the sensory cells and their cilia and villi. Endocytosis of villous material was noted in the sensory cells in newly formed ocelli, and the polymorphic profiles of autophagocytosis were present in very early stages of pigmented cell differentiation. The small pigment granules appeared to arise from a granular material present in the cytoplasm, and apparently transported from the Golgi apparatus by vesicles. -- The optic region thickened to become a pad of tissue. Establishment of this cushion and numerous ocelli occurred rapidly through regeneration, while the larvae, which developed optic pigmentation and an ocellus after the establishment of their third pairs of tube feet, maintained the single ocellar condition for an extended period of time.

Actions (login required)

View Item