ИСТИНА

Doridacea is a widespread suborder of nudibranch mollusks (Nudibranchia, Gastropoda). Dorids, like all representatives of nudibranch mollusks, are devoid of a shell, but in the process of evolution they acquired spicules — structures that functionally replace it. Despite the fact that the presence of spicules in dorids integuments has been known for a long time, the structure of the spicular apparatus has been studied extremely fragmentary. This paper examines the spicules Acanthodoris pilosa (Abildgaard in Müller, 1789), Adalaria proxima (Alder & Hancock, 1854), Onchidoris muricata (O.F. Müller, 1776) - representatives of Onchidoridae family. The purpose of this work is a comprehensive description of the structure of the spicular apparatus and their comparison. The collection of material was carried out in the summer period 2016-2018 in the Kandalaksha Bay of the White Sea in the vicinity of the N.A. Pertsov White Sea Biological Station. During the research classical methods of light and scanning electron microscopy were used. In the process of this work there was first made comprehensive description of the structure of the spicular tracts with details of the external and internal morphology of the spicules involved in their formation for representatives of Onchidoridae family. We have identified a special structure of the transition zone between the vertical and horizontal paths, the spicules of this area are highlighted in a special type of tract - stellular. It is noted that the method of packing spicules depends on their shape and affects the density of integuments. During comparing the spicular tracts of representatives of the family Onchidoridae, a general plan of the structure of the horizontal tract is noted, as well as significant differences in the structure of the vertical tract. This describes the correlation of the thickness of the integuments with the thickness of the layer of spicules - the thicker the integuments, the smaller the thickness of the spicular tracts.