Mercuria tensiftensis, Boulaassafer, Khadija, Ghamizi, Mohamed & Delicado, Diana, 2018

Boulaassafer, Khadija, Ghamizi, Mohamed & Delicado, Diana, 2018, The genus Mercuria Boeters, 1971 in Morocco: first molecular phylogeny of the genus and description of two new species (Caenogastropoda, Truncatelloidea, Hydrobiidae), ZooKeys 782, pp. 95-128 : 105-109

Mercuria tensiftensis sp. n.

Type material.

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).

Other material.

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).

Diagnosis.

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.

Description.

Shell ovate-conic, whorls 4-5, height 3-5.1 mm (Figure 13 A–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.

Operculum as for genus, orange to brownish, about two whorls; muscle attachment area oval and located near the nucleus (Figure 13 J–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 14 B–C). Inner marginal teeth bearing 13-16 cusps and outer marginal with 15-21 cusps (Figure 14D, F; Suppl. material 1: Table 2).

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 15 D–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 15 E–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 15 G–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).

Etymology.

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

Distribution.

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

Remarks.

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.

Ecology.

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 .