KINGSLEY, Roni J.*; WONG, Eric; FROELICH, Jenna; MARKS, Carolyn; University of Richmond; University of Richmond; University of Richmond; University of Richmond: Spine Formation in Deep-Sea Hydrothermal Vent Aplacophoran Molluscs

The aplacophora are a specialized class of molluscs with a derived vermiform shape. They are indigenous to all oceans and are typically found in deep-sea sediment. Most are small, measuring a few millimeters in length. These mollusks lack a shell, but instead are covered with spines or spicules. This study examines spine formation in neomenioid aplacophorans collected by Dr. Cindy Lee Van Dover (The College of William and Mary) from hydrothermal vents of the northern East Pacific Rise. Using scanning electron microscopy, the spines, which cover the entire body surface, have been found to be partially hollow. X-ray microanalysis reveals that they are composed of calcium carbonate. Transmission electron microscopy, reveals an epidermis consisting of a cuticle embedded with spines. When decalcified, an organic matrix is found within the spines. Early spine formation appears to begin intracellularly within vacuoles of spine-secreting cells in the mantle epithelium. Auxiliary cells adjacent to the epidermal cells containing the developing spines are apparently involved in spine formation. As the spines develop they emerge from the intracellular environment. Spines emerging from spine-forming vacuoles generate microvilli-lined cup-like structure. Mature spines protrude from the epithelium into the extracellular environment leaving an undulating epidermal surface.