Mercuria bakeri 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 : 96

Mercuria bakeri Gloeer, Boeters & Walther, 2015

Examined material.

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).

Revised diagnosis.

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).

Description.

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).

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.

Distribution.

Only known from the type locality.

Remarks.

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 ).

Ecology.

See Glöer et al. (2015).