Development studies on the globiferous pedicelleriae of the echinoid strongylocentrotus drobachiensis O.F. Muller with special emphasis on the skeleton

Moore, Sylvia Lillian Broderick (1975) Development studies on the globiferous pedicelleriae of the echinoid strongylocentrotus drobachiensis O.F. Muller with special emphasis on the skeleton. Masters thesis, Memorial University of Newfoundland.

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Abstract

Developmental stages of the globiferous pedicrellariae of the sea urchin Strongylocentrotus Drobachiensis O. F. Muller were investigated with a view to understanding the development and differentiation of the skeletal elements, muscles, sensory areas, nerves and venom glands. Specimens were studied using the light microscope, the transmission electron microscope, the scanning electron microscope, and the analytical electron microscope. -- A globiferous pedicellaria begins as a tiny finger-shaped projection on the test of the sea urchin. The tip gradually separates into three jaws which continue to merge with each other at their bases. The skeleton is one of the first components to develop in the appendage. A skeletal element is deposited in the three jaws and in the basal stalk region. The skeleton remains surrounded by a cluster of cells throughout development. These cells send out numerous projections which are continuous with thin areas of cytoplasm surrounding, or near the skeleton; mitochondria are numerous in the cytoplasmic projections. X-ray microprobe analysis with EMMA-4 showed significantly high amounts of calcium in the cells associated with the skeleton especially in the mitochondria, vehicular structures and nuclei. The term calcicyte (L. calx, lime) has been proposed to refer to this skeletogenic cell type. – The skeletal valves of the jaws develop from a tri-radiate spicule into a very elaborate ossicle with areas for articulation, muscle insertion and passage of nerve fibers. -- Unlike the mature appendage, the developing pedicellaria possesses an epithelium on the outer sides of the jaws that is several cell layers thick. This has been shown to develop into the venom glands. -- The sensory hillock appears as a thickening of the epithelium on the inner side of each jaw. Nerves from the sensory hillocks enter the skeletal valves through a foramen to innervate the muscles which insert on the skeleton.

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