The First Record of Stenothoe cf. tergestina (Nebeski 1881) (Crustacea, Amphipoda, Stenothoidae) in the Black Sea

Numerous individuals of an amphipod previously unreported from the Black Sea were found in 2017 on structures of a mussel and oyster marine farm, near the outer roadstead of Sevastopol Bay, Crimea. The species discovered was morphologically especially similar to Stenothoe tergestina (Nebeski 1881) and provisionally identified as Stenothoe cf. tergestina. The morphology, population structure, and ecology of this species were studied. An analysis of the population structure of S. cf. tergestina in the years 2017–2022 showed that adult females, males, and juveniles were present in the samples year round. The animals preferred to dwell on surfaces overgrown with periphyton colonies of the hydroid polyp of the genus Aglaophenia Lamouroux 1812. In the collections of amphipods from the periphyton of the farm structures, S. cf. tergestina turned out to be the most abundant (70–90% of the total number of identified amphipod individuals). The length of adult females was up to 4.5 mm, while it reached up to 3.6 mm in males.