RADOMANIOLA NACHTIGALLAE SP. NOV.

(FIGS 16, 17)

Z o o b a n k r e g i s t r a t i o n: z o o b a n k. org:act: 0139AB61-FB6A-42C4-814A-78E132AAEC1A

Etymology: Named after Silvia Nachtigall, who helped us with much of the preparation of material and the laboratory work conducted for this and other studies.

Type material: Holotype (MNCN 15.05 /200165), ten paratypes (MNCN 15.05 /200166) in the MNCN collection and> 100 paratypes (UGSB 18857) in the UGSB collection. Type locality: source of the Krupa River, Krupa na Vrbasu, Bosnia and Herzegovina.

Material studied: Source of the Krupa River, Krupa na Vrbasu, Bosnia and Herzegovina, 44.6207°N, 1 7. 1 1 0 5°E, T.H. a n d D.D., Ju n e 2 0 1 6, M N C N 15.05/200166 and UGSB 18857 (80% ethanol) .

Diagnosis: Protoconch microsculpture slightly wrinkled; central radular tooth formula 7-C-7/1- 1; bursa copulatrix globular, with a long duct; SR1 elongate, duct short; SR2 elongate, duct short; penis slightly pigmented on the distal section, gradually tapering, shorter than head length; nervous system weakly pigmented, moderately concentrated (mean RPG ratio = 0.46).

Description: Shell ovate-conic, four whorls, height 2.2–2.8 mm (Fig. 16A–D; Supporting Information, Table S6). Periostracum yellowish. Protoconch ~550 µm wide, 1.5 whorls; nucleus ~200 µm wide; protoconch microsculpture slightly wrinkled (Fig. 16G). Teleoconch whorls convex, with deep sutures; body whorl large, occupying about three-quarters of total shell length. Aperture slightly oval; inner lip thicker than outer lip; peristome margin simple, straight (Fig. 16B). Umbilicus narrow, not covered by the inner lip. Operculum oval, brownish, about two whorls; muscle attachment area oval and located near the nucleus (Fig. 16E, F). Radular length intermediate, ~650 µm (~25% of total shell length), with ~60 rows of teeth (Fig. 16H). Central tooth formula 7-C-7/1-1 (Fig. 16I); basal tongue U-shaped, length about equal to lateral margin. Lateral tooth formula (5)4-C-4(5). Inner marginal teeth having 30–32 tapered cusps, shortening toward the base. Outer marginal teeth with 35–37 sharp cusps (Fig. 16J).

Animal darkly pigmented except for neck and tentacles (Fig. 17F). Ctenidium with 13–15 welldeveloped gill filaments, occupying ~50% of pallial cavity length and positioned posteriorly. Osphradium of intermediate width and opposite middle of ctenidium (Fig. 17A). Stomach slightly longer than wide, with two chambers almost equal in size; style sac longer than wide, surrounded by an unpigmented intestine (Fig. 17B; Supporting Information, Table S7). Nervous system slightly pigmented, moderately concentrated (mean RPG ratio = 0.46); cerebral ganglia approximately equal in size, presenting small black granules (Fig. 17C).

Female glandular oviduct approximately three times longer than wide. Albumen gland shorter than capsule gland. Bursa copulatrix globular, as long as wide. Bursal duct longer than bursal length. Renal oviduct unpigmented, coiled. SR1 elongate, duct short, joining renal oviduct slightly above the insertion point with bursal duct. SR2 slightly shorter than SR1, elongate, with a short duct, located on renal oviduct near loop (Fig. 17D, E; Supporting Information, Table S8).

Male genitalia with a prostate gland approximately two times longer than wide, bean shaped; seminal duct entering the middle-posterior region; pallial vas deferens emerging close to its anterior edge (Fig. 17H). Penis slightly pigmented on the distal section, gradually tapering, shorter than head length, base medium wide, weakly folded along inner edge and with one medial outgrowth on its left side (Fig. 17F, G; Supporting Information, Table S9); penis attached well behind the right eye; penial duct narrow, near outer edge, almost straight.

Habitat: This species has been found only in a rheocrene spring of clear and shallow waters presenting low temperature (10.5 °C) and conductivity (465 µS/ cm). Aquatic plants are sparse. Snails are abundant on stones. Other co-occurring gastropods are Sadleriana sp. and Ancylus sp.

Remarks: This species is closely related to the geographically proximate congeners R. bosniaca and R. szarowskae . The average COI sequence divergence between R. nachtigallae and these two species is 2% and 4%, respectively. This small genetic divergence contrasts with their considerable morphological differentiation in terms of shell size, shell shape and other characters of the reproductive system. Thus, R. nachtigallae differs from R. bosniaca in that it has a larger shell with taller spire whorls, wider base of penis, shorter penis compared with head length, more globular bursa copulatrix, longer bursal duct and more elongated SR1; and differs from R. szarowskae in its smaller shell, smaller penis and smaller bursa copulatrix (Supporting Information, Figs S2, S 6, S 8). These three species have a similar number of gill filaments and cusps on the radular teeth and RPG ratio.