Mercuria targouasensis Gloeer , Boeters & Walther, 2015

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 : 98-102

Mercuria targouasensis Gloeer, Boeters & Walther, 2015

Mercuria confusa Backhuys & Boeters, 1974: 113

Material.

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).

Revised diagnosis.

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.

Description.

Shell ovate-conic, whorls 3-5, height 2.63-3.43 mm (Figure 7 A–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.

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).

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 9 G–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).

Distribution.

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

Remarks.

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).

Ecology.

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 .