Mercuria egarensis Miller, García-Guerrero & Ramos, 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 : 29-33

Mercuria egarensis Miller, García-Guerrero & Ramos sp. nov.

urn:lsid:zoobank.org:act:F4D85246-8580-48C8-8CFD-7C838D87B6B5

Figs 17–19 ; Supp. file 2: Tables S14–S18

Diagnosis

Shell ovate-conic; aperture obliquely ovate; protoconch microsculpture granulated; periostracum whitish to pale grey; central radular tooth formula (2)3-C-3(2)/1-1; female genitalia with bursa copulatrix pyriform to elongate, ca 2.5–3 times as long as wide; seminal receptacle elongate with short peduncle; penis darkly pigmented, gradually tapering; penial appendix unpigmented, ovate, about equal in length or slightly shorter than the distal end of the penis and medially positioned on the inner edge of the penis; nervous system pigmented, elongate (mean RPG ratio = 0.57); cerebral ganglia approximately equal in size.

Etymology

The name ‘ egarensis ’ refers to the ancient Roman city of Egara, present-day Terrassa, Catalonia, where the species occurs.

Type material

Holotype SPAIN • sex unknown (dry preserved); Barcelona, Font de les Canyes ; MNCN 15.05/200174H .

Paratypes SPAIN • 38 specs (preserved in ethanol 80%, 10 dissected and 3 processed for DNA sequencing); same collection data as for holotype; MNCN 15.05/94752 • 13 specs (preserved in ethanol 80%); same collection data as for holotype; MNCN 15.05/94753 • 25 specs (preserved in ethanol 80%); same collection data as for holotype; MZB 2021-2798 • 1 spec. (dry preserved); same collection data as for holotype; NHMW 113529 • 2 specs (dry preserved); same collection data as for holotype; RMNH. MOL.507925 • 1 spec. (dry preserved); same collection data as for holotype; JPM-586 • 1 spec. (dry preserved); same collection data as for holotype; MCP • 1 spec. (dry preserved); same collection data as for holotype; MCP.

Type locality

Font de les Canyes, Catalonia, Spain 41.586217° N, 2.038500° E, 340 m a.s.l.

Description

MEASUREMENTS. Holotype: SL = 3.32 mm, SW = 2.53 mm, SL/SW = 1.31, AH = 1.51 mm, SL-LBW = 0.86 mm, WBW = 2.05 mm, AL = 1.61 mm, AW= 1.23 mm, WPW = 1.22 mm, WAW = 0.70 mm.

SHELL. Ovate-conic, whorls 4–5, height 3–4.3 mm, width 1.7–2.8 mm ( Fig. 17A–E ; Supp. file 2: Table S14); periostracum whitish to pale grey; protoconch of 1.5 whorls, ca 350 µm wide, nucleus ca 150 µm wide ( Fig. 18A ); protoconch microsculpture granulated ( Fig. 18B–C ). 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; umbilicus narrow, not covered by the inner lip ( Fig. 17A–E ).

OPERCULUM. As for the genus, orange to brown, sometimes yellowish, about two whorls; muscle attachment oval, located near the nucleus ( Fig. 17F–G ).

RADULA. Length intermediate, ca 800 µm long (35% of total shell length), containing about 55 rows of teeth. Central tooth formula (2)3-C-3(2)/1-1, central cusp V shaped, cutting edge slightly concave ( Fig. 18D ). Lateral tooth formula (3)2-C-2(3), central cusp V shaped and slightly longer than the central tooth one. Inner marginal teeth with 11–15 cusps; outer marginal teeth with 15–17 cusps ( Fig. 18E–F ). Radular data were obtained from specimens from the type locality.

PIGMENTATION AND ANATOMY. Animal slightly brownish to darkly pigmented ( Fig. 19C ); 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; 19–23 gill filaments; filaments broad, triangular, fused at the base by an epithelium ( Fig. 19D ). Osphradium elongate, more than 3 times as long as broad, 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, protruding anteriorly into the intestinal loop ( Fig. 19E ). Intestine unpigmented, continuing on as a straight rectum.

MALE GENITALIA. Prostate gland bean-shaped, about 2 times as long as wide (Supp. file 2: Table S18), connected by the posterior vas deferens to a convoluted seminal vesicle and the testis. Penis darkly pigmented, gradually tapering, attached to the neck behind the right eye; penial appendix unpigmented, ovate, about equal in length or slightly shorter than the distal end of the penis and medially positioned on the inner edge of the penis ( Fig. 19F ).

FEMALE GENITALIA. Glandular oviduct 2.5 times as long as wide; albumen gland longer than capsule gland ( Fig. 19A ); bursa copulatrix pyriform to elongate ( Fig. 19A–B ), ca 2.5–3 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 ( Fig. 19B ).

NERVOUS SYSTEM. Pigmented, elongate (mean RPG ratio = 0.57; see Supp. file 2: Table S15); cerebral ganglia approximately equal in size and have small black dots of pigment; pleuro-supraoesophageal connective ca 7 times as long as pleuro-suboesophageal one ( Fig. 19G ).

Ecology and distribution

The species is endemic to the Font de les Canyes Spring, alongside the Besós River. The conductivity of this spring is relatively high (1412 µS/cm). The species was collected from the rocky bottom of the spring at a low abundance. No other snail species were found in the spring. The water is used for human consumption, which may have had an impact on this and other snail populations.

A series of sampling campaigns of this and nearby areas were carried out between 2016 and 2018 and the species was not found elsewhere. The spring, located in a small zone in the eastern part of the municipality of Terrassa, discharges to the Besós River basin. Watercourses from the western part of the municipality drain into the Llobregat River basin (Jordi Corbella pers. com.). Bofill & Haas (1920) cited M. similis from Terrassa; however, as the drainage of this spring is associated with another hydrological basin, it is unlikely that Bofill & Haas (1920) citation for M. similis corresponds to Font de les Canyes.

Remarks

Mercuria egarensis sp. nov. differs from the closely related species M. carrillorum sp. nov. by having a slightly shorter penis, a larger penial appendix, a longer radular ribbon, a larger number of cusps on the central radular tooth [(2)3–C–3(2)/1–1 vs (3)4–C–4(3)/1–1], a more concentrated perioesophageal ring, a pyriform SR1 positioned on the renal oviduct just above the junction with the bursal duct (in M. carrillorum , it is positioned at the junction) and the absence of a pallial tentacle. Regarding their ecology, the two species differ in their conductivity preferences, with M. egarensis occurring in waters with higher conductivity.

Mercuria egarensis sp. nov. does not resemble any of the congeners found in the Catalonia region. However, according to our PCA results, M. egarensis and M. balearica have overlapping shell shape variation ( Fig. 3 ), though the latter presents a more globose shell with a wider aperture ( Fig. 11 ). Although M. egarensis also resembles M. tachoensis and M. similis in terms of shell shape, its granulated protoconch microsculpture discriminates it from the pitted one in M. tachoensis . The shape and colouration of the penial appendix differentiate M. egarensis from M. similis : it is highly ovate and unpigmented in the former species and triangular and pigmented in the latter.

The sequence divergence of COI indicated that M. egarensis sp. nov. is closely related to M. carrillorum sp. nov. with a divergence of only 1.3%. Mercuria egarensis diverges 3.7% with M. similis and 8.1% with M. balearica . The species is most distantly related to M. tensiftensis and M. melitensis , diverging with both at around 9% ( Miller et al. 2022).

Figures

Fig. 17. Shells and operculum of Mercuria egarensis Miller, García-Guerrero & Ramos sp. nov. A–B. Holotype (MNCN 15.05/200174H), frontal and lateral views. C–G. Paratypes (MNCN 15.05/94753). F. Operculum, inner side. G. Operculum, outer side.

Fig. 18. Protoconch and radula of Mercuria egarensis Miller, García-Guerrero & Ramos sp. nov. from Font de les Canyes, Barcelona, Spain.A. Details of the protoconch.B. Protoconch nucleus.C. Protoconch microsculpture. D. Overview of radular teeth rows. E–F. Detailed view of the inner and outer marginal teeth, respectively.

Fig. 19. Anatomy of Mercuria egarensis Miller, García-Guerrero & Ramos sp. nov. from Font de les Canyes, Barcelona, Spain. A. Female genitalia. B. Detailed view of the bursa copulatrix and seminal receptacle. C. Head and penis. D. Ctenidium and osphradium. E. Stomach. F. Prostate gland. G. Perioesophageal ring.

Fig. 3. Principal components analysis plot for species of Mercuria Boeters, 1971 based on 21 coordinates (9 landmarks and 12 semilandmarks). Each dot on the plot represents the consensus of the shape of each of the sampled populations. Warp grid deformations (TPS) show expansion (in red colour) and contraction (in blue) of the shell shape.

Fig. 11. Shells and operculum of Mercuria balearica (Paladilhe, 1869). A–B, G–H. Stream at Sant Joan de Carbonell, Minorca, Spain. C. Colarsega River, near the Port of Mahon (type locality). D. Fuente Árabe Spring, Mojácar, Granada, Spain (unpigmented specimen). E. Venta El Pilar Spring, Málaga, Spain. F. Spring, Alozaina, Cádiz, Spain. G. Operculum, inner side. H. Operculum, outer side.