Atyaephyra acheronensis Christodoulou, Antoniou, Antonios Magoulas & Athanasios Koukouras 2012

Rostrum long, dorsal margin straight, 6.28–6.66 × as long as high, equal to or longer than scaphocerite. 19–26 pre orbital teeth on dorsal margin of rostrum arranged up to tip. With 1–3 post orbital teeth and 3–8 teeth on ventral margin of rostrum (Fig. 11A). Carapace smooth with pterygostomial angle not protruding, rounded (Fig. 11B). Pleuron of fifth abdominal segment pointed with an acute posterior angle (Fig. 11C). Telsonwith four pairs of dorsal spines arranged in curved fashion (Fig. 11D). Distal border of telson with 12–15 spines (6–8 pairs) arranged in a fan-like pattern. Outermost pair of spines shortest, similar to dorsal spines, adjacent pair stronger terminating before the finely setulose, inner pairs (Figs 11D–E). Antennulary stylocerite with its tip failing to reach or reaching distal margin of basal peduncle segment. Anterolateral lobe of basal segment short and round (Fig. 11G). Distal segment of antennular peduncle with 1–2 spines (Fig. 11F). Basal lower endite of maxilla densely covered with long simple setae arranged in 18–20 oblique parallel rows. Endite of maxilla 1.56–1.65 × as long as basal lower endite (Fig. 12G). Basal endite of first maxilliped reaching clearly beyond distal end of exopod (Fig. 12F). Distal one-third of terminal segment of third maxilliped bearing 1–5 mesial spines and one subdistal lateral spine near the base of larger terminal spine, interpretable as dactylus (Fig. 12H). Armature along flexor margin of dactylus of third and fourth pereiopod consisting of 5–7 and 6–7 spines respectively (Figs 12B, 12D). Merus of third and fourth pereiopod with 4–6 and 3–4 spines respectively (Figs 12A, 12C). Armature along flexor margin of dactylus of fifth pereiopod consisting of 27–38 spines (Fig. 12E). Endopod of first male pleopod expanded proximally and with a distal portion elongated (ribbon shaped) and tapering. Endopod with 18 spines arranged on a slightly curved inner margin and 12 setae arranged on outer margin (Fig. 12I). 579–1117 eggs of 0.40–0.55 × 0.25–0.35 mm in size.

Atyaephyra acheronensis sp. n. is found in freshwater habitats of Croatia (Krka River), Slovenia (Dragonja River) and Greece (Acherontas River and Louros River) (see material examined and Fig. 1). Although this study was based on a limited number of specimens, it is postulated that Atyaephyra acheronensis sp. n. occurs in more rivers covering an area ranging from Croatia to Greece.