ИСТИНА

Tantulocarida is a small subclass of parasitic Crustacea that exclusively utilize other crustaceans as hosts. Both larval and adult stages are among the smallest arthropods, and the tantulus larva can be considered as the smallest segmented crustacean larva known so far. The complex life cycle of these parasites which includes both parthenogenetic and sexual phases has not yet been fully reconstructed and their phylogenetic position within the Pancrustacea still remains elusive. Two species of Tantulocarida, Arcticotantulus pertzovi Kornev, Tchesunov & Rybnikov, 2004 and Microdajus tchesunovi Kolbasov & Savchenko, 2010, representing different families and infesting different host categories (harpacticoid copepods and tanaidaceans) were discovered in the White Sea in the early 2000s. Various aspects of their internal anatomy, phylogenetic position and biology have been studied since. A preliminar phylogenetic analysis based on 18S rDNA sequences of both White Sea species resolved the Tantulocarida as sistergroup to the Cirripedia within the Thecostraca. This result requires additional confirmation using a more extensive molecular dataset; however, morphological evidence in support of a close relationship between tantulocaridans and barnacles is provided by the presence and structure of the cement gland, which produces gluing material for the larva to settle down. The anatomy of the tantulus larva has been studied using CLSM, TEM and SEM, demonstrating that the tantulus larva undergoes significant changes once it is permanently attached to the host. These modifications include the release of cement followed by quick degradation of the cement gland, disintegration of muscular structures and formation of the rootlet system. Similar studies on the adult male revealed the presence of a so-called honeycomb-like structure located in front of the brain which is tentatively identified as a gonad. Populations of both tantulocaridan species were studied during various seasons in the vicinity of the WSBS and revealed seasonal changes in the ratios of the various life cycle stages. Several attempts to obtain the sexual female in the White Sea have remained fruitless so far. However, the presence of an as yet undescribed nauplius stage in meiobenthic samples suggests that the absence of sexual females in previous surveys is due to sampling bias.