Аннотация:AimDuring last decades, the integrative taxonomy became a most popular approach to define and describe taxa on different taxonomic levels. However, it is often hard to implement it in taxa with sparse or extremely variable morphological characters. Sponges of the genus Leucosolenia (Calcarea, Calcaronea) encounter more than 40 species distributed worldwide. The systematics history of this group is complicated with different species conceptions proposed by various researches. The main goal of our study is to revise the diversity and taxonomy of the genus Leucosolenia from the White Sea using integrative approach. The additional aims of the study are identifying phylogenetically significant morphological characters and proposing optimal sets of molecular markers for further researches of calcareous sponges.Methods Molecular sampling included more than 250 individuals from the White Sea (Russia), Netherlands and Brittany (France). Molecular study included 18S, 28S and H3 markers and implemented Bayesian and Maximum likelihood phylogenetic approaches. Species delimitation and intraspecific divergence were investigated with ABGD and TCS-based analysis. Morphological analysis included studies of external morphology, general skeletal morphology, spicule morphology and cytology using light and electron microscopy.ResultsIntegrative analysis showed that diversity of the genus Leucosolenia in the White Sea is represented by four species: L. variabilis, L. corallorrhiza and two species new to science. Leucosolenia complicata is restricted to NE Atlantic. Examination of morphological characters revealed a strong correlation between morphology of studied Leucosolenia species and their position on the phylogenetic tree. Species differ in general skeletal organization, spicule set and cellular composition. Main conclusionThe integrative taxonomical approach, which included molecular studies with three markers and detailed morphological studies, made it possible to clarify the hidden diversity the genus Leucosolenia in White Sea.The study was supported by RSF n°17-14-01089 (ultrastructural studies), RFBR nos°19-04-00563 and 19-04-00545.