ИСТИНА

Patellogastropoda is the basal group of Gastropoda, fundamentally different from other gastropods by a morphological features, one of which is a docoglossate (stereoglossate) radula. Patellogastropods have a stereoglossate feeding stroke while all other gastropod and non-gastropod outgroups are flexoglossate (Guralnik and Smith, 1999). According to the latest data, the stereoglossate condition of the radula in patellogastropods is secondary (Haszprunar 1988a; Salvini-Plawen 1988; Ponder and Lindberg 1997), and the flexoglossic state is primary for all mollusks (Colgan et all., 2003). These conclusions were based on morphological data radula of adult animals. A comparative morphological analysis of the larval radula of various gastropods can be an important addition to clarifying the basal condition of the radula of all mollusks. Since the patellogastropods are the basal group of the Gastropoda, the establishment and synthesis of the larval radula is of particular interest. Testudinalia tesulata habitats on the border of the intertidal and upper subtidal zones of the White Sea. External fertilization occurs in the water at the beginning of June. Spiral cleavage is an equal. One division at a temperature of +10 g passes every 2.5-3 hours. One day after the fertilization, an early trochophore is formed, which does not move, ciliary cells do not form prototroch. The trochophore about 30-39 hours is started to swim. It is with the apical cilia, the slit-like blastopore is almost closed, and on the dorsal side the shell gland is formed, which is still concave inward. After 10 hours (48-54 hours), the velum develops, the telotroch shifts to the ventral side, there is a foot bud and a shell begins to form. Veliger for 90 hours after fertilization has a well-developed shell, which begins to calcify, foot, well-translucent liver through the shell and the rudiments of tentacles. A radula also develops, it consists of three teeth in a row and nine rows, while at the 88-hour stage, radula have not been fined. Most likely the torsion occurs after 100 hours, while the torsion veliger has a well-developed operculum, already a white shell and rather long head tentacles. By 170 hours, the process of sedimentation begins, with the larvae floating-settling, eyes and well-developed tentacles, the test is completely calcified. It was possible to trace the development to 264 hours, the veliger only crawled, but a complete metamorphosis did not occur. There are numerous studies of the development of Patellogastropoda (for example, Smith, 1935; Crofts, 1954; Bigelaar, 1977; Wanninger et all., 2000; Kostyuchenko et al., 2013) and our data coincide with those obtained earlier. It is important to note that the development is asynchronous and in the one group were detected at different stages of development. It is also significant that when the temperature is higher on several degrees, the development takes place at least twice as fast (Kozin et al., 2013). New fact that we find is that the radula of the patellogastropods is triserial with central and lateral teeth, as well as described for polyplacophores (Minichev, Sirenko, 1974). And in the adult state of Testudinalia tesulata, the radala consists of four teeth in a row (with the central tooth being reduced). The information obtained rather gives rise to new questions: at what point does the central tooth reduce and add more lateral pairs, does the pattern of formation of one tooth remain in the larval and adult state or does it change, do there are common patterns in the formation of the larval radula in patellogastropods and other groups of mollusks with flexoglossate radala ? To answer these questions, we need new data on the fine morphology of the larval radula and data on the tabulation and formation of the radula in other groups of mollusks.