Studies of the structure, arrangement and mode of operation of cnidae from cnidarians belonging to the classes Cubozoa, Hydrozoa, Scyphozoa and Anthozoa

Abstract

The cnidoms of Chironex fleckeri (Class Cubozoa), Lytocarpus philippinus (Class Hydrozoa), Cyanea capillata (Class Scyphozoa), a species of Cerianthus and Stichodactyla haddoni (both members of the Class Anthozoa) are presented. Two new types of heteroneme are described. Inadequacies of the cnida classification system currently in use are highlighted in this study. A new classification system rectifying these inadequacies whilst retaining most of the current terminology, and incorporating cnida types discovered recently is presented. The general histology of the tentacles of each species is examined with emphasis on the ectodermal layer and the arrangement of cnidae. The tentacles of Chironex fleckeri are comprised of an ectoderm and an endoderm separated by a mesogloea containing a tubulo-muscular system. There are three types of fibre (or filament) that are involved with movement in the tentacle. Nematocytes and accessory cells are aggregated in the ectodermal layer in bands which can be moved closer together or further apart. There is a definite pattern in the arrangement of different types of nematocyst in the bands. This is described as is the movement of developing nematocysts which give rise to the pattern. The weals exhibited by a victim of C. fleckeri stinging reflect the manner in which nematocysts are arranged on tentacles. In other species studied ectoderm, endoderm and mesogloea are present in the tentacles. Although a tubulo- muscular system is present in the hydrozoan and scyphozoan studied, it is absent from the anthozoans studied. Distinct patterns in the arrangement of nematocysts on the tentacles of all species studied (except for Sticliodactyla haddoni) were noted but these patterns vary from species to species. During studies of the ultrastructure of the tentacles of Chironex fleckeri, it was found that mastigophore-bearing cells possess a cnidocil apparatus, several radially-oriented fibres containing microtubules, and a capsule. The cnidocil apparatus consists of a flagellum surrounded by two series of microvilli. Basal cytoplasmic extensions of the microvilli are woven into a fibrillar basket. Extending from the basket are fibrous bundles which, in turn, are attached to the radially-oriented fibres. These fibres may act in conjunction with those of neighbouring accessory cells either to expose the apical end of the nematocyte or to remove it from the firing line. All species studied possess radial fibres or filaments in the basal ends of cnidocytes. Apart from Chironex fleckeri only cnidocytes of the species of Cerianthus studied possess microtubules in these regions. Like the cnidocytes of C. fleckerif those of Lytocarpus philippinus and Cyanea capillata each possesses a cnidocil apparatus. Cnidocytes of Cerianthus sp. marginal tentacles and Stichodactyla haddoni tentacles possess the putative sensory structures, ciliiary cones, at their apical surfaces. Ciliary cones are not present in the cnidocytes of the oral tentacles of Cerianthus sp. In the cerianthid studied nematocysts do not possess tripartite flaps and the spirocysts and spirocytes appear structurally different from those described in other species. As is the case with Chironex fleckeri nematocytes, fibrillar baskets surround the hydrozoan and scyphozoan nematocysts studied but are absent from the anthozoan cnidocytes. Studies of isolated mastigophores of all five species have revealed granular electron dense material inside undischarged tubes. This material is chemically different from the material in the capsule. Tube contents are released continuously as the tube everts. Penetrants of Chironex fleckeri are closed at their tips. Capsular contents are released once the occlusion at the tube tip is ruptured. Material from nematocyst tubes appears to be be injected intravenously in mice, a prerequisite for the production of systemic effects. When subjected to a series of electrical stimuli, the cnidae of each species studied show different thresholds for cnida discharge. There is also a highly variable response to a group of reagents tested for their ability to elicit discharge of cnidae on the tentacles of the five species. The response to each reagent varies even between members of the same class and of the same species. This study has shown that currently there is no universal inactivator of cnida discharge for cnidae of all species. Vinegar, widely advocated for use as a cnida discharge inhibitor is ineffective for use with the cnidae of many species. However, the study has shown the value of using venom inactivators. Studies of the mode of envenomation, activation and inhibition of cnida discharge and deactivation of venom contained within isolated cnidae have important implications for treatment of stings.