Mercuria veronicae Miller, Khalloufi & Delicado, 2023

Miller, Jonathan P., Delicado, Diana, García-Guerrero, Fernando, Khalloufi, Noureddine & Ramos, Marian A., 2023, Morphology and taxonomic assessment of eight genetic clades of Mercuria Boeters, 1971 (Caenogastropoda, Hydrobiidae), with the description of five new species, European Journal of Taxonomy 866 (1), pp. 1-63 : 47-52

Mercuria veronicae Miller, Khalloufi & Delicado sp. nov.

urn:lsid:zoobank.org:act:986C0653-973B-4C3D-9A4A-C6A216321EBE

Figs 29–31 ; Supp. file 2: Tables S14–S18

Diagnosis

Shell ovate-conic; aperture obliquely ovate; periostracum whitish to pale grey; central radular tooth formula (5)4-C-4(5)/1-1; female genitalia with a bursa copulatrix pyriform to elongate, ca 2 times as long as wide; seminal receptacle elongate; penis darkly pigmented; penial appendix slightly pigmented, ovate, shorter than or equal in length to the distal end of the penis, medially positioned on the inner edge of the penis; nervous system pigmented, elongate (mean RPG ratio = 0.55); cerebral ganglia approximately equal in size; pleuro-supraoesophageal connective ca 11 times as long as pleuro-suboesophageal one.

Etymology

After Veronica Ruiz, the first author’s grandmother.

Type material

Holotype TUNISIA • sex unknown (preserved in ethanol 80%); Tozeur, Tamerza, Oasis Waterfall. El Waha Spring ; MNCN 15.05/200124H .

Paratypes TUNISIA • 3 specs (preserved in ethanol 80%); same collection data as for holotype; MNCN 15.05/200124P • 15 specs (preserved in ethanol 80%, 6 dissected and 1 processed for DNA sequencing); same collection data as for holotype; UGSB 17271 .

Additional material examined

TUNISIA • 15 specs; Tozeur, Tamerza, Big Waterfall, Lekbir Spring ; UGSB 17274 • 4 specs; Tozeur, Echbika, Echbika Waterfall, Echbicka Spring ; UGSB 17276 .

Additional locality information provided in Supp. file 1: Table S1.

Type locality

El Waha Spring, Oasis Waterfall, Tamerza, Tozeur, Tunisia, 34.381933° N, 7.933450° E, 278.67 m a.s.l.

Description

MEASUREMENTS. Holotype: SL = 4.87 mm, SW = 3.56 mm, SL/SW = 1.36, AH = 2.03 mm, SL-LBW = 1.40 mm, WBW = 2.96 mm, AL = XX mm, AW = 2.06 mm, WPW = 1.67 mm, WAW = 0.85 mm.

SHELL. Ovate-conic, whorls 4–5, height 3.25–5.3 mm, width 2.5–4 mm ( Fig. 29A–F ; Supp. file 2: Table S14); periostracum whitish to pale grey; protoconch of 1.5 whorls, ca 250 µm wide, nucleus ca 150 µm wide; teleoconch whorls slightly convex, separated by a deep suture; body whorl large, convex, occupying about two-thirds of the total shell length; aperture obliquely broad ovate, complete; inner lip thicker than outer lip; aperture margin straight; inner lip touching the body whorl; umbilicus narrow, not covered by the inner lip.

OPERCULUM. As for the genus, orange to brown, sometimes yellowish, about two whorls; muscle attachment oval, located near the nucleus ( Fig. 29G–H ).

RADULA. Length intermediate, ca 750 µm long (35% of total shell length), containing about 60 rows of teeth ( Fig. 30A ). Central tooth formula (5)4-C-4(5)/1-1, central cusp V shaped, cutting edge concave ( Fig. 30B–C ). Lateral tooth formula (3)4-C-4(3), central cusp V shaped and slightly longer than the central tooth one. Inner marginal teeth with 11–15 cusps; outer marginal teeth with 21–25 cusps ( Fig. 30D ). Radular data were collected from the following specimens: UGSB 17271 – El Waha Spring, Oasis Waterfall, Tamerza, Tozeur, Tunisia; UGSB 17274 – Lekbir Spring, Big Waterfall, Tamerza, Tozeur, Tunisia; UGSB 17276 – Echbicka Spring, Echbika Waterfall, Echbika, Tozeur, Tunisia.

PIGMENTATION AND ANATOMY. Animal darkly pigmented ( Fig. 31A, D ); head and tentacles dark brown, pigmentation lighter on eye lobes, snout and neck; snout about as long as wide, approximately parallel-sided, with medium distal lobation. Ctenidium occupying almost the total length of the pallial cavity; 28– 33 gill filaments; filaments broad, triangular, fused at the base by an epithelium ( Fig. 31B ). Osphradium elongate, more than 3 times as long as wide, positioned opposite middle of ctenidium. Stomach almost as long as wide with two chambers almost equal in size (Supp. file 2: Table S16); style sac longer than wide, with the unpigmented intestine surrounding its distal part and continuing on as a straight rectum ( Fig. 31C ).

MALE GENITALIA. Prostate gland bean-shaped, about 2 times as long as wide (Supp. file 2: Table S18). Pallial vas deferens emerge close to both the anterior edge of the prostate and the external margin of the penis ( Fig. 31F ). Penis darkly pigmented, gradually tapering, attached to the neck behind the right eye, distal end of the penis broad, triangular; penial appendix pyriform, shorter than or about to the same length as the distal end of the penis, slightly pigmented at the junction with the penis, medially positioned on the inner edge of the penis ( Fig. 31D–E ).

FEMALE GENITALIA. Glandular oviduct 2.5 times as long as wide, albumen gland longer than capsule gland; bursa copulatrix elongate, ca 2 times as long as wide (Supp. file 2: Table S17); bursal duct shorter than bursa copulatrix; renal oviduct unpigmented, highly coiled with three loops; seminal receptacle elongate, with a short duct, positioned on the distal part of the renal oviduct just above the junction with the bursal duct.

NERVOUS SYSTEM. Pigmented, elongate (mean RPG ratio = 0.55; see Supp. file 2: Table S15); cerebral ganglia approximately equal in size; pleuro-supraoesophageal connective ca 11 times as long as pleuro-suboesophageal one ( Fig. 31G–H ).

Ecology and distribution

The studied samples of this species come from three localities in the Tozeur region, north of the Chotts, but its distribution extends to other regions around the Chotts el Gharsa and Djeride (Gafsa, Kebili, Nefzaoua and Gabes). It occurs in streams, springs and irrigation ditches of the oasis areas. This species is present at a high density (more than 3000 ind./m 2) on the edge of the streams, where the flow is low and the substrate muddy, and attached to aquatic plants. The main streams of Tamarza (Oued Frid) and Echbika (Oued Echbika) are highly saline (conductivity 8667 and 3945 µS/cm, respectively) and flow over an alluvial and clayey-sandy substrate of the Plio-Quaternary, with a predominance of sulphate-sodium, gypsum and phosphorites ( Abidi 2007). Co-occurring species are Galba truncatula , Physella acuta ( Draparnaud, 1805) (in low abundance), Eupaludestrina spp. , Melanoides tuberculata (O.F. Müller, 1774) , Melanopsis douvillei Pallary, 1916 and Melanopsis praemorsa (Linnaeus, 1758) (in high abundance).

Remarks

Intraspecies morphological differences were observed mainly in the penial features of males from the same population ( Fig. 31D–E ). Some individuals have a much-atrophied penis. Such variation may be parasite-induced, similar to the case reported in another species of Mercuria ( Boulaassafer et al. 2018) . Parasitized females also presented an atrophied pallial oviduct, making it difficult to conduct a complete anatomical study. The pigmentation of the penis is also very variable, ranging from very slight to pronounced dark pigmentation at the junction between the appendix and distal end of the penis.

Mercuria veronicae sp. nov. differs from the phylogenetically closely related species M. lupiaensis sp. nov. and M. melitensis by having a high-spired shell and a more elongated bursa copulatrix compared with M. lupiaensis and thinner inner and outer shell lips compared with the characteristically thick ones of M. melitensis ( Glöer et al. 2015) . Mercuria veronicae also has a long, triangular and more pigmented penial appendix compared with the short (to very short), ovate and slightly pigmented or unpigmented one in M. lupiaensis . In M. melitensis , the penial appendix is only as long as the distal end of the penis. Compared with other geographically proximate species, M. veronicae resembles M. pycnocheilia (Bourguignat, 1862) in shell shape, although the latter presents a thicker inner shell lip (see Glöer et al. 2010) and the former, has smaller-sized shells. In addition, Glöer et al. (2010) and Glöer (2019) noted the acute apex of M. pycnocheilia (Bourguignat, 1862) , which is not present in M. veronicae . Shell shape features also distinguish the new species from M. globulina ( Letourneux & Bourguignat, 1887) , which has a larger, more slender shell, and M. bourguignati Glöer, Bouzid & Boeters, 2010 , which has a larger shell and smaller aperture (about half the shell length in M. bourguignati vs about three quarters the shell length in M. veronicae ). The anatomy of these geographically proximate species is unknown.

According to our sequence divergence estimates of COI, M. veronicae sp. nov. is most similar to M. lupiaensis sp. nov. (average divergence of 3.9%) and diverges most with M. tensiftensis (by 8.4%) ( Miller et al. 2022).

Figures

Fig. 29. Shells and operculum ofMercuria veronicaeMiller, Khalloufi & Delicado sp. nov.A–B. Holotype (MNCN 15.05/200124H), frontal and lateral views. C–D. Paratypes. C. MNCN 15.05/200124P. D. UGSB 17271. A–D, G–H. El Waha Spring, Oasis Waterfall, Tamerza, Tozeur. E–F. Lekbir Spring, Big Waterfall, Tamerza, Tozeur. G. Operculum, inner side. H. Operculum, outer side.

Fig. 30. Radula of the Mercuria veronicae Miller, Khalloufi & Delicado sp. nov. from El Waha Spring, Tozeur. A. General view of the radular ribbon. B. Overview of radular teeth rows. C. Detailed view of the central teeth. D. Detailed view of the outer marginal teeth.

Fig. 31. Anatomy of the Mercuria veronicae Miller, Khalloufi & Delicado sp. nov. from Spring El Waha, Tozeur, Tunisia. A. Head. B. Ctenidium and osphradium. C. Stomach. D. Head of a male. E. Penis. F. Prostate gland. G. Head with perioesophageal ring attached. H. Perioesophageal ring.