Abstract
Cnidarians are characterized by the presence of stinging cells containing nematocysts, a sophisticated injection system targeted mainly at prey-capture and defense. In the anthozoan subclass Octocorallia nematocytes have been considered to exist only in low numbers, to be small, and all of the ancestral atrichous-isorhiza type. This study, in contrast, revealed numerous nematocytes in the octocoral Heteroxenia fuscescens. The study demonstrates the applicability of cresyl-violet dye for differential staining and stimulating discharge of the nematocysts. In addition to the atrichous isorhiza-type of nematocysts, a novel type of macrobasic-mastigophore nematocysts was found, featuring a shaft, uniquely comprised of three loops and densely packed arrow-like spines. In contrast to the view that octocorals possess a single type of nematocyst, Heteroxenia fuscescens features two distinct types, indicating for the first time the diversification and complexity of nematocysts for Octocorallia.
Highlights
Within certain epithelial cells of members of the phylum Cnidaria there are distinct intracellular secretion products, known as nematocysts [1,2]
scanning-electron microscopy (SEM) micrographs revealed numerous nematocytes exposed on the gastrodermis, some entangled with the cilia (Fig. 2a)
Our preliminary work has indicated that nematocysts of H. fuscescens are not stained by the commonly used hematoxylin and Nematocyst characterization The thread tubule of the atrichous isorhiza type, isolated from the gastrovascular cavity, has a uniform diameter along its entire length (Fig. 4a) and an open tip (Fig. 4b)
Summary
Within certain epithelial cells of members of the phylum Cnidaria there are distinct intracellular secretion products, known as nematocysts [1,2]. They are commonly found in the body, and especially in the tentacles, of jellyfish, hydroids, sea anemones, and corals, and are used for capturing food, defense against predation and, in certain cases, for adherence to a substrate [1,2]. Schmidt [10] studied nematocysts in Alcyonium digitatum, Cornularia cornucopiae, Parerythropodium coralloides, Pseudopterogorgia aerosa and Paralcyonium elegans (Alcyonacea), as well as in Pteroeides spinosum and Veretillum cynomorium (Pennatulacea), all of which featured solely the atrichous isorhiza type. Jimbo [14] revealed on both the nematocysts and on the zooxanthellae surface in Sinularia lochmodes (Alcyonacea), a D-galactose binding lectin (SLL-2), indicating the possibility of a lectin-mediated hostsymbiont interaction
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