ИСТИНА

Conoidea is the superfamily of marine gastropods, with over 5,000 valid species (WoRMS, http://www.marinespecies.org). The foregut of various members of the Conoidea is characterized by the presence of a retractile proboscis, one or two pairs of salivary glands, the radula sac is positioned at the base of the proboscis (i.e. at an angle to the axis of the proboscis) rather than on the tip, a venom gland which produces the cocktail of various physiologically active toxin peptides used both for attacking prey and as defiance against predators (Dutertre et al., 2014; Puillandre, Fedosov & Kantor, 2016), and the distinctive feeding mechanism. Radula is variable in Conoidea in the number of teeth in a transverse row (from five to two) and in the morphology of the teeth. General radula morphology has been studied in detail (Taylor et al., 1993; Kantor & Taylor, 2002; Bouchet et al., 2011). Based on the teeth number in a row and the morphology of the marginal teeth several types of radula have been described. The main role in the feeding is taken by the marginal teeth. The morphology of the marginal teeth is not correlated with the number of teeth in a row. The two most commonly found types of marginal teeth are duplex and hypodermic (both are used on the proboscis tip). A duplex tooth consists of a robust, pointed, major element and a smaller, more slender, accessory limb. The major elements of the marginal teeth are attached to the radular membrane along most of their length and only the tips are free. Another, unique for the conoideans type, is characterised by ‘hypodermic’marginal radular tooth, which is a hollow harpoon with holes at the base and tip. The poison is injected into the pray through the central tooth cavity like syringe needles. This represent the most intricate radular morphology among gastropods and is found in several independent lineages of Conoidea, including the best-known family Conidae (cone snails). In this family the vestigial radular membrane may be present or absent and only a pair of hypodermic marginal teeth occurs in each transverse row. The hypodermic marginal tooth, as can be seen from transverse sections, is formed from a plate that is rolled to create a tube with overlapping edges. In the Conidae, the wall of the tooth is formed by several layers, but in other families of conoideans with hypodermic teeth the overlap is less marked and the wall is formed by no more than two layers (see Bouchet et al., 2011, fig. 3C). The teeth of the conoidean taxa are considerably altered during tooth maturation in contrast to other gastropods (Kantor & Taylor, 2000). Duplex marginal tooth develops from a “flat plate through thickening of the tooth edges and elevation of the posterior edge from the radular membrane as opposed to or the lengthwise folding of a nearly-flat plate once it progresses half way along the radula” (Sibogasyrinx Powell, 1969, Cochlespiridae; Kantor, Fedosov & Puillandre, 2018). The process of tooth formation and maturation is much less studied. We studied the radula of three species of different families of Conoidea (Lophiothoma (Turridae), Clavus (Drillidae), Conus pulicarius (Conidae)) by light and electron microscopy. The radula of these species is significantly different from each other. Conus pulicarius have a hypodermic tooth without radular membrane. The radula of Lophiotoma consists of the two dagger-like marginal teeth attached to the radular membrane. The radula of Clavus consist of small central tooth, paired marginal denticulated teeth and pair of dagger-like marginal teeth. The radular membrane is well developed. Despite of the differences in the radula general morphology, there are lot of similarities in radular formation of studied species: ultrathin morphology of odontoblasts; odontoblasts number which form one marginal tooth; localization of the odontoblasts in the blind end of the radular sac; position of the marginal teeth; V-shaped configuration of the membrane in the radular sac. The main difference is the ultrathin morphology of the subradular epithelium which contains numerous tonofilaments in Conus while this epithelium is electron-transparent in Clavus and Lophiotoma. This morphology could be explained by functions of these cells. The epithelium of Conus participates in the enrolling of the tooth while other two species have radula membrane and the subradular epithelium probably strengthen the membrane. Thus, we may conclude that despite large differences in radular morphology the main patterns of the radula formation are similar throughout the superfamily. This work was supported by the Russian Foundation for Basic Research, 19-04-00501. The histological investigations were sup- ported by grant 14-50-00029 from the Russian Science Foundation.