Review of

Macropodia czernjawskii (Brandt, 1880), described from the Black Sea, was ignored in the regional faunal accounts for more than a century, although it was recognised in the Mediterranean. Instead, M. longirostris (Fabricius, 1775) and M. rostrata (Linnaeus, 1761) were frequently listed for the Black Sea. We selected a lectotype and redescribed the species on the basis of the type series from the Crimean Peninsula and the new material collected in the Black Sea. Historical and new collections, as well as the analysis of publications, indicate that M. czernjawskii is the only Macropodia species occurring in the Black Sea. Molecular barcode (COI gene marker) data show that M. czernjawskii is a species well-diverged from other studied species of the group. Furthermore, M. parva van Noort & Adema, 1985 has very low genetic distances from M. rostrata and M. longipes A. Milne-Edwards & Bouvier, 1899 is indistinguishable from M. tenuirostris (Leach, 1814), using COI sequences. The respective synonimisations, supported by morphological data, are proposed. M. czernjawskii is a Black Sea – Mediterranean endemic occurring also in the neighbouring Atlantic coastal zone of the Iberian Peninsula and occupying shallower depth, compared to other Mediterranean species of Macropodia. As an upper subtidal inshore species, it is particularly specialised in self-decoration and stimulates abundant epibiosis, providing masking and protection. The bulk of epibiosis consists of algae and cyanobacteria. Amongst the 25 autotrophic eukaryote taxa, identified to the lowest possible level, green chlorophytes Cladophora sp. and calcareous rhodophytes Corallinales gen. sp. were most commonly recorded. Non-indigenous red alga Bonnemaisonia hamifera Hariot, first officially recorded at the Caucasian coast of the Black Sea in 2015, was present in the epibiosis of M. czernjawskii in Crimea as early as 2011.