MOROCCO. Paratype (one male): UGSB 18986, Taghramt, 3.5 km towards N, Tangier-Titouan, 23/03/2014 (35°48.912'N, 5°27.618'W).

Shell ovate-conic; periostracum greyish; body whorl large, convex, occupying approximately 3/4 of total shell length; aperture ovate and complete; umbilicus narrow, not covered by the inner lip; central radular tooth formula (3)4–C–4(3)/1–1; bursa copulatrix elongate; bursal duct shorter than bursa length; one seminal receptacle fingerlike, with a short duct; penis strap-like, pigmented from brown to dark grey; penial appendix unpigmented, shorter than penis, base wide, medially positioned on inner edge of penis; nervous system moderately concentrated (mean RPG ratio = 0.40).

Shell ovate-conic (Figure 2), height 3.0–3.5 mm (Glöer et al. 2015). Periostracum greyish. Teleoconch whorls convex, separated by deep sutures. Body whorl occupying approximately 3/4 of total shell length. Umbilicus narrow, partially covered by the inner lip. Aperture ovate, complete, in contact with the body whorl; inner lip thicker than outer lip.

Radula with approximately 65 rows of teeth (Figure 3A), medium sized (23% total shell length), 7.5 times longer than wide. Central tooth formula (3)4–C–4(3)/1–1; central cusp long, V-shaped. Lateral tooth formula 3–C–3; central cusp long, V-shaped (Figure 3B, C). Inner and outer marginal teeth having approx. 16 and 20 pointed cusps, respectively (Figure 3D).

Figure 3. 

Radulae, A–D M. bakeri, Taghramt E–H M. tingitana, Tangier at 11 km towards Ksar es Seghir. A, E Radulae ribbons B, F Overview of rows of radulae teeth C, G Central tooth D Outer marginal tooth H Inner marginal and lateral teeth.

Head brown pigmented except for white patches surrounding tentacles and eyes (Figure 4A). Ctenidium well-developed, with ca. 21 gill filaments, occupying most of pallial cavity; osphradium elongate, positioned middle of ctenidium (Figure 4C). Bursa copulatrix elongate. Bursal duct shorter than bursa length. Seminal receptacle fingerlike, with a short duct, joining renal oviduct above the insertion point with bursal duct (based on Glöer et al. 2015). Penis strap-like, attached to central area of head. Penis brown to dark grey pigmented. Penial appendix and base of penis unpigmented. Penial appendix shorter than penis, base wide, medially positioned on inner edge of penis (Figure 4B). Terminal gland large, occupying the whole distal end of the appendix.

Figure 4. 

Male genitalia and ctenidium, M. bakeri, Taghramt. A Head with penis B Penis C Ctenidium.

Only known from the type locality.

Based on a short fragment of the mitochondrial COI gene, our phylogenetic analysis depicts M. bakeri as sister to M. tingitana with a mean uncorrected sequence divergence of 3.4%. A greater genetic distance is not unexpected when including longer sequences. Despite this relatively low genetic distance, morphological differences between these two species are striking, especially in terms of penis shape (penis slender, 3.5 times longer than appendix in M. bakeri and penis and appendix almost equal in size in M. tingitana) and seminal receptacle (longer in M. bakeri than M. tingitana).

See Glöer et al. (2015).

MOROCCO. Paratypes (two females): UGSB 17658, Tangier at 11 km towards Ksar es Seghir, 22/03/2014 (35°49.008'N, 5°43.643'W).

Shell ovate-conic, whorls 4–5; periostracum greyish; body whorl large, convex, approx. three-quarters of shell length; aperture ovate and complete; umbilicus narrow, not covered by the inner lip; central radular tooth formula 4–C–4/1–1; bursa copulatrix pyriform to elongate, with a short duct; one seminal receptacle elongate, without duct; penis small, black pigmented; penial appendix as long as penis, slightly pigmented, base wide, distally positioned on inner edge of penis.

Shell ovate-conic, whorls 4–5, height 2.9–3.6 mm (Figure 5A; Suppl. material 1: Table 1). Body whorl large, approx. two-thirds total shell length. Teleoconch whorls shouldered, separated by deep sutures. Periostracum greyish. Aperture ovate, complete, in contact with the body whorl; inner lip thicker than outer lip; peristome margin straight (Figure 5B). Umbilicus narrow, partially covered by the inner lip.

Figure 5. 

Shells and opercula, M. tingitana, Tangier at 11 km towards Ksar es Seghir. A, B Shells, C, D Opercula (inner, outer sides).

Operculum as for genus, brownish, whorls 2.5. Muscle attachment area oval located near the nucleus (Figure 5C, D). Radula length intermediate, approx. 600 µm long (20% total shell length), six times longer than wide, with 50–60 rows of teeth (Figure 3E; Suppl. material 1: Table 2). Central tooth formula 4–C–4/1–1; central cusps tongue-shaped. Lateral tooth formula 3–C–3; central cusp long, V-shaped (Figure 3F–H). Inner marginal teeth with 15–16 pointed cusps. Outer marginal teeth with 21–23 cusps (Suppl. material 1: Table 2).

Animal black pigmented except for neck and eye lobes. Ctenidium well-developed, with 19–23 gill filaments, occupying almost entire length of the pallial cavity. Osphradium elongate, positioned posterior to middle of ctenidium (Figure 6A). Stomach nearly as long as wide; style sac slightly shorter than stomach and surrounded by an unpigmented intestine (Suppl. material 1: Table 3). Glandular oviduct approx. three times longer than wide. Capsule gland shorter and thicker than albumen gland. Renal oviduct coiled, unpigmented. Bursa copulatrix pyriform to elongate, with a short duct. Seminal receptacle small, elongate, sessile, joining renal oviduct above the insertion point with bursal duct (Figure 6B, C; Suppl. material 1: Table 4). Penis attached to central area of head. Penis and penial appendix almost equal in length. Penis black pigmented, short, and triangular. Penial appendix and base of penis unpigmented. Terminal gland small (see Glöer et al. 2015).

Figure 6. 

Ctenidium and female genitalia, M. tingitana, Tangier at 11 km towards Ksar es Seghir. A Ctenidium B Pallial oviduct C Seminal receptacle (SR) and renal oviduct (RO).

Only known from the type locality.

Mercuria tingitana can be distinguished from its congeners in northern Africa by its slender shell and short penis. Genetically, the closest species to M. tingitana is M. bakeri. However, both these are the most distant species to other Moroccan congeners with an uncorrected pairwise distance range of 4.7–8.5% for M. tingitana and of 4.7–6.8% for M. bakeri. Mercuria midarensis sp. n. and M. emiliana are the most genetically distant from M. tingitana according to COI divergences of 8.5% and 8.2%, respectively (Table 2).

See Glöer et al. (2015).

Examined material. MOROCCO. MHNM 18 ZTMH10, UGSB 17912, Oum Rbii Springs, N of Khenifera, 01/06/2015 (33°3.2059'N, 5°24.8797'W); MHNM 18 ZTMH11, UGSB 17955, a small ditch in Mirleft, 02/02/2015 (29°35.0167'N, 10°1.845'W).

Shell ovate-conic, whorls 3–5; periostracum whitish; body whorl occupying more than three-quarters of total shell length; aperture ovate; umbilicus narrow, partially covered by the inner lip; operculum brownish to slightly orange; central radular tooth formula 3–C–3/1–1; bursa copulatrix elongate, with a short duct; one seminal receptacle pyriform, with a short duct; penis gradually tapering, grey; penial appendix shorter than penis, grey, base wide, medially positioned on inner edge of penis; nervous system extremely elongated (mean RPG ratio = 0.70), gently black pigmented.

Shell ovate-conic, whorls 3–5, height 2.63–3.43 mm (Figure 7A–C; Suppl. material 1: Table 1). Periostracum whitish. Protoconch with two whorls, diameter ca. 600 µm; nucleus ca. 140 µm wide (Figure 7H); protoconch microsculpture granulated (Figure 7I). Teleoconch whorls convex, separated by deep sutures. Body whorl large, occupying three-quarters of total shell length. Aperture ovate, complete, in contact with the body whorl; inner lip thicker than outer lip; peristome margin straight (Figure 7D, E). Umbilicus narrow, partially covered by the inner lip.

Figure 7. 

Shells and opercula, M. targouasensis. A, B, E Shell, Oum Rbii Springs C, D Shell, a small ditch in Mirleft F, G Opercula (inner, outer sides), Oum Rbii Springs H, I Protoconch and detailed microsculpture of protoconch, Oum Rbii Springs.

Operculum as for genus, light orange to brown, whorls 2; muscle attachment area near nucleus (Figure 7F, G). Radula length intermediate, ca. 800 µm long (20% total shell length), seven times longer than wide, with approx. 50 rows of teeth (Fig. 8A; Suppl. material 1: Table 2). Central tooth formula 3–C–3/1–1; central cusp tapered, long. Lateral teeth formula (4)3–C–3(4); central cusp wide, V-shaped (Figure 8B, D–F). Inner and outer marginal teeth having 11–15 and 14–18 cusps, respectively (Figure 8C, F).

Figure 8. 

Radulae, M. targouasensis. A–D Oum Rbii Springs E, F A small ditch in Mirleft. A Radular ribbon B, E Central tooth C, D, F Inner marginal, outer marginal, and lateral teeth.

Animal black pigmented except for pale area surrounding eye lobes and neck (Figure 9G, H). Ctenidium well-developed, with 19–25 gill filaments, occupying almost entire length of the pallial cavity. Osphradium elongate, positioned approximate middle of ctenidium (Figure 9A). Stomach nearly as long as wide; style sac slightly shorter than stomach, surrounded by an unpigmented intestine (Figure 9B; Suppl. material 1: Table 3). Glandular oviduct three times longer than wide. Capsule gland longer and thicker than albumen gland. Bursa copulatrix pyriform to elongate, with a short duct. Renal oviduct unpigmented, coiled, making three loops. Seminal receptacle pyriform, with a short duct, joining renal oviduct above the insertion point with bursal duct (Figure 9D, E; Suppl. material 1: Table 4). Prostate gland bean-shaped, ca. 2.5 times longer than wide (Figure 9F; Suppl. material 1: Table 5); seminal duct entering the posterior region; pallial vas deferens emerging close to its anterior edge. Penis gradually tapering, attached to the area close to the right eye. Penial appendix slightly pigmented, shorter than penis, base wide, middle positioned on inner edge of penis. Terminal gland large, occupying the whole distal end of the appendix (Figure 9G–J; Suppl. material 1: Table 5). Nervous system gently pigmented, extremely elongated (mean RPG ratio = 0.70; Suppl. material 1: Table 6); cerebral ganglia equal in size and shape (Figure 9C).

Figure 9. 

Anatomical structures, M. targouasensis. A–F, H A small ditch in Mirleft G, I–J Oum Rbii Springs. A Ctenidium B Stomach C Partial nervous system D Pallial oviduct E Bursa copulatrix and seminal receptacle F Prostate gland G, H Head with penis I, J Head and penis drawings. RO renal oviduct SR seminal receptacle.

This species was found in coastal streams in southwestern Morocco and in a spring-fed habitat in the Middle Atlas.

The morphological and anatomical descriptions presented here are based on specimens collected at two sites: one in the Mirleft region, 70 km from the type locality, (i.e., ford Oued Assaka), and another, in a more remote place in the Middle Atlas Mountains. The population collected in the surroundings of Mirleft may correspond to the species Mercuria ‘mirlheftensis’ (nomen nudum) from the same area suggested by García et al. (2010). However, the name M. ‘mirlheftensis’ is not valid. Specimens collected in the Mirleft area resemble specimens from the type locality of M. targouasensis regarding the shape of the penis and prostate, and also of the female genitalia, especially bursa copulatrix shape. Based on the geographic proximity of these two localities and the similarity in shell and anatomical characters of their specimens, we assigned the population from Mirleft to M. targouasensis. Specimens from Oum Rbii (Middle Atlas) were also tentatively assigned to this species based on shell and morphological similarities and a short genetic distance (1.3%) between this and the Mirleft population. However, this assignment needs confirmation in future systematic studies on Mercuria, which should include these and other Mediterranean species.

Mercuria targouasensis and M. midarensis sp. n. are sister species and differ molecularly by 2.1%–3.4% (mean sequence divergence 2.8%). The two species are close in shell dimensions but differ in other shell features such as the relative size of the body whorl (larger in M. targouasensis) or the umbilicus (wider in M. midarensis sp. n.). They also differ anatomically; Mercuria midarensis sp. n. has typically a strap-like penis, 2.5 times longer than head length, a small penial appendix with narrow insertion into the penis, and an elongate bursa copulatrix, whereas in M. targouasensis, the penis is more often gradually tapering, equal or 1.5 times longer than head length, the penial appendix is larger with a wider insertion, and the bursa copulatrix is pyriform to elongate. These two species also differ in the number of cusps on radular teeth (Suppl. material 1: Table 2).

In the new localities of M. targouasensis, this species was found attached to stones in a saltwater spring in the Middle Atlas (ca. 1,200 m a.s.l. altitude, and 37.9 PSU, practical salinity unit) and in the sediment of a ditch in the region of Mirleft cohabiting with Melanopsis praemorsa.

Holotype, MNCN 15.05/200019H (Ethanol 80%), a small ditch 7 km from Midar, Northern Morocco, 34°54.5795'N, 3°34.0292'W, 03/06/2015, leg. K.B., M.G., D.D., T.H. Paratypes MNCN 15.05/200019P, UGSB 17921, and MHNM 18 ZTMH12 (from the same lot).

MOROCCO. MHNM 18 ZTMH20, UGSB 17921, UGSB 17922, a small ditch 7 km from Midar, 03/06/2015 (34°54.5795'N, 3°34.0292'W); MHNM 18 ZTMH13, UGSB 19933, Selouan River, S of Nador, 30/04/2016 (35°4.6117'N, 2°55.485'W); MHNM 18 ZTMH14, UGSB 19939, Ouzej River, Al Aaroui, 30/04/2016, (35°0.3634'N, 2°59.5133'W); UGSB 19935, Cherarba ponds W of Saidia, 28/04/2016 (35°6.3116'N, 2°20.75'W); MHNM 18 ZTMH15, UGSB 19934, Izerouan River, 20 km W of Nador, 12/05/2015 (35°9.8333'N, 3°6.6'W); MHNM 18 ZTMH16, UGSB 19940, Mariouari River, 30/04/2016 (35°18.36'N, 2°58.6483'W); MHNM 18 ZTMH17, UGSB 19938, Messoussate River, Selouan, 02/05/2016 (35°3.81'N, 2°54.383'W). SPAIN. MHNM 18 ZTMH18, UGSB 19937, Rio de Oro, Melilla, 18/05/2015, (35°17.2483'N, 2°56.6283'W).

Shell ovate-conic, whorls 4–5; periostracum whitish; body whorl large, convex, occupying more than three-quarters of total shell length; aperture ovate, complete; umbilicus narrow, not covered by the inner lip; protoconch microsculpture granulated; operculum dark orange to dark brown; central radular tooth formula (3)4–C–4(3)/1–1; bursa copulatrix elongate, with a short duct; one seminal receptacle elongate without duct; penis gradually tapering to strap-like, light to dark grey pigmented; penial appendix similarly pigmented, shorter than penis, base wide, medially positioned on inner edge of penis; nervous system extremely elongated (mean RPG ratio = 0.70), slightly pigmented.

Shell ovate-conic, whorls 4–5, height 3–4.7 mm (Figure 10A–J; Suppl. material 1: Table 1). Periostracum whitish. Protoconch ca. 400 µm wide, whorls 1.5; nucleus ca. 125 µm wide; protoconch microsculpture granulated (Figure 10K–L). Teleoconch whorls shouldered, separated by deep sutures. Body whorl large, occupying three-quarters of total shell length. Aperture ovate, complete, sometimes in contact with the body whorl; inner lip thicker than outer lip; peristome margin straight (Figure 10I–J). Umbilicus narrow, not covered by the inner lip.

Figure 10. 

Shells and opercula, M. midarensis sp. n. A, I Holotype MNCN 15.05/200019H B Shell, a small ditch 7 km from Midar C Shell, Selouan River D Shell, Ouzej River E Shell, Cherarba ponds F Shell, Mariouari River G Shell, Rio de Oro H Shell, Izerouan River M, N Opercula (inner, outer sides), a small ditch 7 km from Midar K, L Protoconch and detailed microsculpture of protoconch, Selouan River.

Operculum as for genus, dark orange to dark brown, surrounded by a thin and transparent border, whorls 2, muscle attachment area oval and located near the nucleus (Figure 10M–N). Radula length intermediate, ca. 900 µm long (23% total shell length), 7.5 times longer than wide (Figure 11A, F; Suppl. material 1: Table 2); 53–67 rows of teeth. Central tooth formula (3)4–C–4(3)/1–1; central cusp V-shaped, long (Figure 11B–D, G–I). Lateral tooth formula (2)3–C–3(2); central cusp tongue-shaped (Figure 11J). Inner marginal teeth with 12–14 long, pointed, cusps. Outer marginal teeth bearing 18–20 cusps (Figure 11E–J, Suppl. material 1: Table 2).

Figure 11. 

Radulae, M. midarensis sp. n. A–D Selouan River E A small ditch 7 km from Midar F, H–J Rio de Oro G Izerouan River. A, F Radulae ribbons B, G Overview of rows of radulae teeth C, D, H, I Central tooth E, J Inner marginal, outer marginal, and lateral teeth.

Head and tentacles dark brown pigmented; eye lobes and snout margin unpigmented; pigmentation lighter on neck (Figure 12G–H). Ctenidium well developed, with 21–26 gill filaments, occupying most of pallial cavity. Osphradium elongate, positioned opposite middle of the ctenidium (Figure 12A). Stomach slightly longer than wide; style sac shorter than stomach, surrounded by an unpigmented intestine (Figure 12B, Suppl. material 1: Table 3). Glandular oviduct from two to three times longer than wide. Albumen gland shorter than capsule gland. Bursa copulatrix elongate, from two to three times longer than wide. Bursal duct very short. Renal oviduct unpigmented, coiled. Seminal receptacle elongate, without duct (Figure 12D–F, J, Suppl. material 1: Table 4). Prostate gland bean-shaped, approx. two times longer than wide (Figure 12I). Seminal duct entering the posterior region and pallial vas deferens emerging close to its anterior edge. Penis gradually tapering to strap-like, attached well behind right eye, base large and slightly pigmented. Penis tapering, light grey pigmented. Penial appendix light grey, shorter than penis, two times longer than wide, base wide, medially positioned on inner edge of penis (Figure 12G–H, K–L; Suppl. material 1: Table 5). Terminal gland large, occupying the whole distal end of the appendix. Nervous system slightly pigmented, extremely elongated (mean RPG ratio 0.70; Suppl. material 1: Table 6); cerebral ganglia almost equal in size and shape (Figure 12C).

Figure 12. 

Anatomical structures, M. midarensis sp. n. A–C, E, G, I, K–L a small ditch 7 km from Midar D Ouzej River F Rio de Oro H Selouan River. A Ctenidium B Stomach C Partial nervous system D Pallial oviduct E, F Bursa copulatrix and seminal receptacle J Bursa copulatrix drawing G, H Head with penis I Prostate gland K, L Penis drawings. RO renal oviduct SR seminal receptacle.

This species is named midarensis after Midar, the nearby city where this species was collected for first time.

Mercuria midarensis sp. n. is distributed mostly in spring-fed and riverine habitats of northeastern Morocco and the surroundings of the Spanish city of Melilla.

The mean uncorrected sequence divergence within Mercuria midarensis was 1.8%, ranging from 0%–3.4%. Despite their geographic proximity, M. midarensis populations were genetically resolved into two geographically separate groups: the northern populations, i.e. those from the Mariouari River, Rio de Oro, and Izerouan River basins; and the southern ones, i.e. ditch in Midar (type locality), Selouan River, Ouzej River, and Cherarba Ponds. Although mean genetic distances between these two groups of populations were relatively high ranging from 2.6% to 3.4% for COI, we found no consistent morphological differences to consider them distinct. However, we did observe shell variability within each group. For most localities, shell length mostly ranged from 3.0 mm to 4.5 mm, with the body whorl occupying 75–82% total shell length. As exceptions, specimens from the Mariouari and Selouan river basins had larger shells (4.0–5.5 mm and 3.6–4.8 mm, respectively) and a body whorl occupying 60–75% total shell length (Figure 10C, F). Although female genitalia morphology and morphometry were similar in all populations of the species, we detected variability in penis shape and size. Both the southern populations and the population from the Rio de Oro basin (within the northern group) are characterized by a long penis (2.1–3.2 mm), 2 to 3 times longer than the appendix and 1.5 to 3 times longer than the head. In contrast, northern populations have a shorter penis (0.6–2.1 mm), which is 2.6 to 4 times longer than the appendix. Moreover, in the population from the Izerouan River basin, the penis is 1.4 to 1.8 times longer than the head while it is shorter than the head in the population from the Mariouari River basin.

Mercuria bakeri and M. tingitana have more elongate, tall-spired shells than most of the populations of M. midarensis sp. n., except for specimens from the Mariouari and Selouan rivers. Mercuria midarensis sp. n. differs from M. bakeri in its shorter seminal receptacle, shorter bursal duct, and larger penial appendix, and from M. tingitana in its longer seminal receptacle, larger penis, and fewer cusps on the radular teeth. The mean genetic distance between M. bakeri and M. midarensis sp. n. was 6.8% while between the latter and M. tingitana it was 8.5%.

Most specimens were found in small ditches or river tributaries attached to stones or simply in the sediment. Mercuria midarensis sp. n. co-occurs with other gastropod species such as Melanopsis praemorsa, Galba truncatula, Ancylus fluviatilis, and Physella acuta.

Holotype, MNCN 15.05/200018H (ethanol 80%), a ditch in Sidi Bouzid, Chichaoua, Morocco, 31°29.6133'N, 8°47.1116'W, 28/11/2015, K.B., M.G. Paratypes MNCN 15.05/200018P, UGSB 17910, and MHNM 18 ZTMH4 (from the same lot).

MOROCCO. MHNM 18 ZTMH19, UGSB 17910, ditch in Sidi Bouzid, Chichaoua, 28/11/2015 (31°29.6133'N, 8°47.1116'W); MHNM 18 ZTMH5, UGSB 17914, a pond near Lahjar Spring, Essaouira, 28/11/2015 (31°38.7583'N, 9°35.0983'W); MHNM 18 ZTMH6, UGSB 17918, ditch in Haddada Bouzerktoun, Essaouira, 28/11/2015 (31°37.95'N, 9°35.0983'W); MHNM 18 ZTMH7, UGSB 19944, ditch in Agadir N’tachraft, 34 km S of Marrakesh, 20/02/2017 (31°23.0917'N, 8°7.353'W); MHNM 18 ZTMH8, UGSB 19945, a spring near Lalla Takerkoust dam, 34 km S of Marrakesh, 20/02/2017 (31°22.5491'N, 8°7.638'W); MHNM 18 ZTMH9, UGSB 19946, Talkount, 80 km E of Marrakesh, 21/02/2017 (31°40.5775'N, 7°16.0298'W).

Shell ovate-conic, whorls 4–5; periostracum whitish, exceptionally yellowish; body whorl large, convex, occupying approx. two-thirds of total shell length; umbilicus narrow, not covered by the inner lip; aperture ovate; protoconch microsculpture grooved; central radula tooth formula (5)4–C–4(5)/1–1; bursa copulatrix elongate, with a short duct; one seminal receptacle elongate, with a short duct; penis gradually tapering; penial appendix dark pigmented, rectangular, shorter than penis, base narrow and black pigmented, medially positioned on inner edge of penis; nervous system elongated (mean RPG ratio = 0.64), slightly pigmented.

Shell ovate-conic, whorls 4–5, height 3–5.1 mm (Figure 13A–G; Suppl. material 1: Table 1). Periostracum whitish. Protoconch ca. 400 µm wide, whorls 1.5; nucleus ca. 125 µm wide (Figure 13H); protoconch microsculpture grooved (Figure 13I). Teleoconch whorls convex, with deep sutures. Body whorl large, occupying approx. two-thirds of total shell length. Aperture ovate, often attached to body whorl on the top; inner lip thicker than outer lip; peristome margin straight narrow (Figure 13D). Umbilicus narrow, not covered by the inner lip.

Figure 13. 

Shells and opercula, M. tensiftensis sp. n. A Holotype MNCN 15.05/200018H, B Shell, ditch in Sidi Bouzid C, D Shell, ditch in Agadir N’tachraft E Shell, ditch in Talkount F Shell, a pond near Lahjar Spring G Shell, a spring near Lalla Takerkoust dam J, K Opercula (inner, outer sides), ditch in Agadir N’tachraft H, I Protoconch and detailed microsculpture of protoconch, ditch in Agadir N’tachraft.

Operculum as for genus, orange to brownish, about two whorls; muscle attachment area oval and located near the nucleus (Figure 13J–K). Radula length intermediate, ca. 900 µm long (25% total shell length), approx. eight times longer than wide; approx. 60 rows of teeth (Figure 14A). Central tooth formula (5)4–C–4(5)/1–1; central cusp V-shaped (Figure 14B, D, E). Lateral tooth formula (4)3–C–3(4); central cusp long, tongue-shaped (Figure 14B–C). Inner marginal teeth bearing 13–16 cusps and outer marginal with 15–21 cusps (Figure 14D, F; Suppl. material 1: Table 2).

Figure 14. 

Radulae, M. tensiftensis sp. n. A, E a spring near Lalla Takerkoust dam B, C a pond near Lahjar Spring D, F ditch in Sidi Bouzid. A Radular ribbon B, D Rows of radular teeth C Lateral tooth and inner marginal teeth E Central tooth F Outer marginal teeth.

Animal darkly pigmented except for neck and tentacles (Figure 15G). Ctenidium well-developed, with 23–27 gill filaments, occupying nearly entire length of pallial cavity. Osphradium elongate, positioned opposite middle of ctenidium (Figure 15A). Stomach slightly longer than wide, with two chambers almost equal in size; style sac longer than wide, surrounded by unpigmented intestine (Figure 15B; Suppl. material 1: Table 3). Glandular oviduct approx. three times as long as wide. Albumen gland longer than capsule gland (Figure 15D–F). Bursa copulatrix elongate, two to three times longer than wide, with a duct shorter than bursal length. Renal oviduct unpigmented, coiled, making 2–3 loops. Seminal receptacle elongate, with a short duct, joining renal oviduct just above the insertion point with bursal duct (Figure 15E–F; Suppl. material 1: Table 4). Prostate gland approx. two times longer than wide, bean-shaped; seminal duct entering the posterior region; pallial vas deferens emerging close to its anterior edge. Penis gradually tapering, attached to the area close to the right eye. Penis dark pigmented, tapering. Penial appendix dark pigmented, shorter than penis, base narrow, medially position on inner edge of penis. Terminal gland occupying the whole distal end of the appendix (Figure 15G–I; Suppl. material 1: Table 5). Nervous system with black granules, elongate (mean RPG ratio 0.64; Suppl. material 1: Table 6); cerebral ganglia approx. equal in size; ganglia darker than connectives and commissures (Figure 15C).

Figure 15. 

Anatomical structures, M. tensiftensis sp. n. A, D, E, G, H ditch in Sidi Bouzid B, F, I a pond near Lahjar Spring C a spring near Lalla Takerkoust dam. A Ctenidium B Stomach C Partial nervous system D Pallial oviduct E, F Bursa copulatrix and seminal receptacle G Head with penis H, I Prostate gland. RO renal oviduct SR seminal receptacle.

The name tensiftensis refers to the hydrological basin (Tensift) where this species was collected.

This species was found in ponds, springs, and ditches in proximal localities of the Tensift River basin in northwestern Morocco.

Shells of this species vary in size (2.4–5.1 mm shell height) and, accordingly, two morphotypes can be distinguished in all populations. One morphotype comprises small to medium-sized shells (2.4–4.0 mm shell height), with slightly shouldered spire whorls and a thick aperture. This morphotype is found in Lahjar, Talkount, and Lalla Takerkoust with an average shell length of 3.5 mm. The second larger group (4.0–5.1 mm shell height) comprises shells with five sloping spire whorls and a thin aperture. This morphotype is well represented in the populations from Sidi Bouzid Springs and Agadir N’tachraft with an average shell length of 4.1 mm. Despite this morphological variation within the species, the estimated genetic distance was 0% for COI.

Two morphotypes of male reproductive organs were also observed in dissected specimens. The most represented is that with a long penis, large appendix, and large prostate gland (localities of Lahjar near Essaouira, Sidi Bouzid, and Lalla Takerkoust dam). However, other dissected males showed a smaller retracted penis and a small degraded prostate gland (localities of Agadir N’tachraft and Talkount). We observed that this second group of males contained parasites known to cause castration in host snails (Lim and Heyneman 1972, Combes and Cheng 1986, Mouahid and Mone 1990, Ashby and Gupta 2014) and propose this as the cause of such variation (see Figure 16). According to our observations in parasitized specimens of different populations, male and female genitalia seem more affected than other organs.

Mercuria tensiftensis sp. n. is characterized by its long shell (the longest shells among Moroccan Mercuria species) and its large and gradually tapering penis with a terminal gland occupying the entire distal end of the penial appendix. The new species differs from M. midarensis sp. n. in its shorter penis (two times vs. three times longer than appendix in M. tensiftensis sp. n. and M. midarensis sp. n., respectively) (Suppl. material 1: Table 5), from M. targouasensis in its more elongate bursa copulatrix (Suppl. material 1: Table 4) and from M. similis in its longer shell and its larger and longer penis. These morphological and anatomical differences were supported by molecular data. Hence, the mean genetic distance between M. tensiftensis sp. n. and M. similis was 6.4% and between the former and M. targouasensis and M. midarensis sp. n. were 6.0% and 6.9%, respectively.

Mercuria tensiftensis sp. n. was found in ditches used for irrigation, springs, and ponds, attached to stones or dead branches in the water. Most of these localities, including the type one, are small water bodies under risk of desiccation or destruction. Co-occurring species were Galba truncatula, Melanopsis praemorsa, and Physella acuta.

Figure 16. 

Head and prostate glands of non-parasitized and parasitized males, M. tensiftensis sp. n. A, B Non-parasitized male, a spring near Lalla Takerkoust dam C, D Non-parasitized male, ditch in Sidi Bouzid E, F Parasitized male, ditch in Sidi Bouzid G–J Parasitized males, ditch in Agadir N’tachraft. Pr prostate gland.