A morphological study of Acanthocephaloides propinquus (Acanthocephala, Arhythmacanthidae) parasitising gobiid fishes (Teleostei, Gobiidae) in the northwestern Black Sea

Morphological data for Acanthocephaloides propinquus (Arhythmacanthidae) from gobiid fishes from the northwestern Black Sea are presented. Individuals from the Black Sea differ from the descriptions based on Mediterranean specimens in having 4–5 proboscis hooks per row in the former and 5–6 in the latter. The size of the cuticular spines is rejected as a diagnostic character for A. propinquus because their length varies in a wide range (3.0–7.5 µm). The diagnostic characters for identifying A. propinquus include the presence of small culticular spines, the testes located in the central part of the body and an acanthor having a single hooklet lacking a root.