ИСТИНА

Onuphidae as a typical Eunicida have complex jaw apparatus consisting of ventral paired mandibles and dorsal serial maxillae. The onuphid maxillary apparatus comprises interconnected elements of a flat carrier and maxillary dentate plates. All studied eunicidan annelids are characterized by replacement of maxillary apparatus in ontogeny, while mandibles were shown to grow throughout the life. Two principally different types of maxillae shedding were described. Dorvilleidae have serial maxillae that interchange during the process of replacement when the first plate is shed into the gut and a new one is formed de novo nearby by a new group of gnathoblasts. Another type of replacement similar to ecdysozoans molting was described in Diopatra aciculata (Onuphidae). In order to clarify this processes we studied shedding of maxillae apparatus in another species of Onuphidae - Mooreonuphis stigmatis utilyzing light, scanning and transmission electron microscopy. M. stigmatis has three generations of maxillae (larval, juvenile and adult) that can be distinguished based on morphology and number of elements. The studies of general and fine morphology of larvae jaws showed that the maxillary elements were formed by a layer of gnatoblasts with short microvilli and a single gnatoblast formed one denticle in each maxillary plate. The next generation of juvenile maxillae was formed by gnathoblasts with long microvilly that penetrated through maxillary plate. It is suggested, that second generation of maxillae has more capacities for continuous growth. The type of jaw replacement from larval to juvenile maxillae in M. stigmatis was similar to one found in Dorvilleidae. The ecdizozoan molting was not reported in the ontogeny of M. stigmatis.