Mercuria similis ( Draparnaud, 1805 )

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 : 8-15

Mercuria similis ( Draparnaud, 1805)

Figs 4–7 ; Supp. file 2: Tables S2–S5

Cyclostoma simile Draparnaud, 1805: 34 , pl. 1 fig 15.

Bythinia meridionalis Risso, 1826: 100 .

Amnicola confusa Frauenfeld, 1863: 1029 .

Amnicola emiliana Paladilhe, 1869: 229 , pl. 19 figs 22–23; 106, pl. 5.

Amnicola compacta Paladilhe, 1869: 110 , pl. 19 figs 14–15.

Paludina cerulea Massot, 1872: 128 .

Amnicola roigiana Salvañá, 1887: 141 .

Amnicola monjoi Chia, 1887: 14 .

Amnicola vallensana Almera & Bofill, 1898: 83 ; pl. III fig. 23.

Paludina similis – Turton & Gray 1840.

Hydrobia similis – Dupuy 1851: 553.

Pseudamnicola confusa – Adam 1940: 1–7, figs 1–2.

Mercuria confusa – Boeters 1971: 178–179, fig. 10.

Pseudamnicola similis – Gasull 1971: 45; pl. II fig. 8.

Mercuria emiliana – Boeters 1988: 208, figs 92–93; 210, figs 118, 125; 211, pl. 3 fig. 34.

non Mercuria meridionalis ( Risso, 1826) – Girardi 2003: 83.

non Pseudamnicola emilianus ( Paladilhe, 1869) – Boeters & Falkner 2017: 251, fig 11i–j.

Revised diagnosis

Shell ovate-conic; aperture obliquely broad ovate; periostracum whitish to grey; protoconch microsculpture granulated; central radular tooth formula (2)3-C-3(2)/1-1; female genitalia with bursa copulatrix pyriform to elongate, ca 3 times as long as wide; seminal receptacle elongate with a short duct; penis darkly pigmented, gradually tapering; penial appendix triangular, variable in length (equal to or shorter/longer than the distal end of the penis), strongly pigmented at the junction with the penis; distal end of the penis triangular; nervous system pigmented, elongate (mean RPG ratio = 0.63); cerebral ganglia approximately equal in size.

Type material (not examined)

Neotype FRANCE • sex unknown; “Gallia meridionalis” [South France]; NHMW-MO 92596 ; designated by Boeters & Falkner (2000).

Type locality

According to original description: “Gallia meridionalis”.

Material examined

FRANCE – Languedoc-Roussillon • 30 specs; Salses-le-Château, Font Dame Spring ; MNCN 15.05/94776 • 30 specs; Salses-le-Château, Font d‘Estramar Spring ; MNCN 15.05/94777 • 30 specs; pond in La Palme ; MNCN 15.05/94778 . – Provence-Alpes-Côte d’Azur • 30 specs; Étang de Berre, stream near La Suriane ; MNCN 15.05/94789 • 30 specs; Étang de Berre, Arc River near Les Cabanes ; MNCN 15.05/94790 • 30 specs; Var, La Foux-de-Draguignan Spring ; MNCN 15.05/94791 .

SPAIN – Granada Prov. • 30 specs; La Malahá Spring ; MNCN 15.05/94758 • La Pucha Spring ; MNCN 15.05/94759 . – Cádiz • 30 specs; Prado del Rey, Pilar de los Playeros Spring ; MNCN 15.05/94760 • 30 specs; Villamartín, La Zarza Spring ; MNCN 15.05/94761 • 30 specs; Medina-Sidonia, El Berrueco Spring ; MNCN 15.05/94803 • 30 specs; Arcos de la Frontera, Platero Spring ; MNCN 15.05/94795 • 30 specs; Puerto Serrano, Pozo Amargo Spring ; MNCN 15.05/94796 • 30 specs; spring in Alcalá de los Gazules ; MNCN 15.05/94797 • 30 specs; Algodonales, El Algarrobo Spring ; MNCN 15.05/94799 • 30 specs; Medina-Sidonia, La Salá Spring ; MNCN 15.05/94800-2546 ; 30 specs; Alcalá de los Gazules, Las Presillas Spring ; MNCN 15.05/94802 . – Guadalajara • 30 specs; saltings of Riba de Santiuste ; MNCN 15.05/94762 • 30 specs; Alcolea Stream, tributary of Salado River , road from Imón to Santamera; MNCN 15.05/94763 • 30 specs; Salado River at Santamera ; MNCN 15.05/94764 , 15.05/94765 • 30 specs; La Vega Stream at Saelices de la Sal ; MNCN 15.05/94766 . – Almería • 30 specs; Las Negras ravine; MNCN 15.05/94767 . – Albacete • 30 specs; Cordovilla saltings; MNCN 15.05/94768 • 30 specs; Casas de Ves, La Salaboreja Spring ; MNCN 15.05/94769 • 30 specs; Casas de Ves, La Cañada Stream near La Salaboreja Spring ; MNCN 15.05/94770 • 30 specs; Fuentealbilla, stream feeding Galayo’s Pond ; MNCN 15.05/94771 . – Zaragoza • 30 specs; Gelsa, stream in Barranco del Agua Salada ; MNCN 15.05/94772 . – Huesca • 30 specs; saltwater stream near Aguinaliu ; MNCN 15.05/94773 • 30 specs; stream crossing the town of Peralta de la Sal ; MNCN 15.05/94774 • 30 specs; Torres del Obispo Spring ; MNCN 15.05/94794 . – Tarragona • 30 specs; Amposta, Ullals de Baltasar ; MNCN 15.05/94780 . – Murcia • 30 specs; Chícamo Stream near La Umbría ; MNCN 15.05/94781 • 30 specs; La Mula River ; MNCN 15.05/94782 • 30 specs; river in Sierra de la Muela ; MNCN 15.05/94742 • 30 specs; Puerto de la Cadena ; MNCN 15.05/94793 . – Castellón • 30 specs; Fuente Amarga Spring ; MNCN 15.05/94783 • 30 specs; marsh at Peñíscola; MNCN 15.05/94786 • 30 specs; irrigation ditch in Moli de la Font ; MNCN 15.05/94787 • 30 specs; irrigation ditch in Cirat ; MNCN 15.05/94788 . – Valencia • 30 specs; Sax, Vinalopó River ; MNCN 15.05/94784 . – Alicante • 30 specs; Braña’s Ravine, near L’Olla Beach ; MNCN 15.05/94785 . – Islas Baleares • 30 specs; Majorca, Albufera of Majorca , Siquia de Son Senyor ; MNCN 15.05/94805 • 30 specs; Majorca, Albufera of Majorca , Siquia d’en Moix ; MNCN 15.05/94806 • 30 specs; Majorca, Muro , Font de Son Sant Joan ; MNCN 15.05/94804 . – Barcelona • 30 specs; El Prat de Llobregat, Estany de la Ricarda Pond ; MNCN 15.05/94779 .

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

Description

SHELL. Ovate-conic, whorls 4–5, height 3.5–5.7 mm, width 1.5–3.3 mm ( Fig. 4 A–O ; Supp. file 2: Table S2); periostracum whitish to grey; protoconch of 1.5 whorls, ca 400 µm wide, nucleus ca 200 µm wide ( Fig. 5A–B ); protoconch microsculpture granulated ( Fig. 5C ); teleoconch whorls very 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 shell wall; 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. 4P–Q ).

RADULA. Length intermediate, ca 800 µm long (35% of total shell length), containing about 65 rows of teeth. Central tooth formula (2)3-C-3(2)/1-1, central cusp V shaped, cutting edge slightly concave ( Fig. 5D–F ). 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 ( Fig. 5E ); outer marginal teeth with 12–25 cusps ( Fig. 5F ). Radular data were collected from the following specimens: MNCN 15.05/94760 – Spring Pilar de los Playeros, Prado del Rey, Cádiz, Spain; MNCN 15.05/94767 – Las Negras ravine, Almería, Spain; MNCN 15.05/94768 – Cordovilla Saltings, Albacete, Spain; MNCN 15.05/94776 – Fonte Dame Spring, Salses-le-Château, Aude, France; MNCN 15.05/94777 – Estramar Spring, Salses-le-Château, Aude, France; MNCN 15.05/94778 – pond in La Palme, Aude, France; MNCN 15.05/94791 – La Foux-de-Draguignan Spring, France and 15.05/94804 – Font de Son Sant Joan, Muro, Majorca, Spain.

PIGMENTATION AND ANATOMY. Animal darkly pigmented, although unpigmented specimens were also found ( Fig. 4E ); head and tentacles black, pigmentation lighter on eye lobes, snout and neck; snout about as long as wide, approximately parallel-sided, with medium distal lobation ( Fig. 7F ). Ctenidium occupying almost the total length of the pallial cavity; 22–27 gill filaments; filaments broad, triangular, fused at the base by an epithelium ( Fig. 6E ). Pallial tentacle present. Osphradium elongate, more than 3 times as long as wide (Supp. file 2: Table S3), positioned opposite middle of ctenidium. Stomach almost as long as wide with two chambers almost equal in size; style sac longer than wide (Supp. file 2: Table S3), with the unpigmented intestine surrounding its distal end before continuing on as a straight rectum ( Fig. 6F ).

FEMALE GENITALIA. Glandular oviduct 2.5 times as long as wide; albumen gland longer than capsule gland ( Fig. 6A–D ; Supp. file 2: Table S4); bursa copulatrix pyriform to elongate, ca 3 times as long as wide; bursal duct shorter than bursa copulatrix; renal oviduct unpigmented, highly coiled with three loops; seminal receptacle elongate, with a short duct, positioned at the distal end of the renal oviduct just above the junction with the bursal duct ( Fig. 6A–D ).

MALE GENITALIA. Penis darkly pigmented, gradually tapering, attached to the neck behind the right eye; penial appendix longer ( Fig. 7A–C ) or shorter ( Fig. 7D–F ) than the distal end of the penis, triangular, strongly pigmented at the junction with the penis, pigmentation gradually weakens from the junction to the middle of the penial appendix where it is very weak. Penial appendix base narrow, medially positioned on the inner edge of the penis. Prostate gland bean-shaped, about 2 times as long as wide, connected by the posterior vas deferens to a convoluted seminal vesicle and the testis ( Fig. 7G–H ; Supp. file 2: Table S5).

NERVOUS SYSTEM. Pigmented, elongate (mean RPG ratio = 0.63; Supp. file 2: Table S15); cerebral ganglia approximately equal in size; pleuro-supraoesophageal connective ca 9 times as long as pleuro-suboesophageal one ( Fig. 6G ).

Ecology and distribution

Most of the examined specimens were found in waters with very high conductivities (592–28 900 µS/cm, average 6364 µS/cm). These localities are affected by the Keuper facies, Mesozoic evaporitic deposits that contain high levels of NaCl and CaSO 4, among others, that dissolve into the superficial waters inhabited by the species. Specimens were most often found in the mud among the lower parts of the shoreline vegetation. Co-occurring gastropod species are Melanopsis spp. , Theodoxus spp. , Belgrandia gibba ( Draparnaud, 1805) , Hydrobia acuta ( Draparnaud, 1805) , Pseudamnicola subproductus ( Paladilhe, 1869) , Diegus gasulli (Boeters, 1981) and Potamopyrgus antipodarum (Gray, 1843) .

The species is distributed in springs, streams, small rivers, coastal lakes (étangs) and ditches near the Mediterranean coast of southern France, the Iberian Peninsula and North Africa ( Boulaassafer et al. 2018) and on the island of Majorca ( Fig. 1 ). It has also been reported near the Atlantic coast of the Iberian Peninsula, northern France, Apennine peninsula, Great Britain and various Atlantic islands ( Wollaston 1878; Kerney 1999; Bodon et al. 2005; Kadolsky 2011). We were unable to confirm previous records of the species for Great Britain ( Baker et al. 1999; Abrehart & Forster 2012), the Azores islands ( Wollaston 1878) and North Africa ( Taybi et al. 2017). Some of these citations may have been incorrectly attributed to M. similis instead of M. tachoensis , which is found in, at least, Great Britain (see below).

Remarks

The material here referred to as M. similis from southern France ( Fig. 4I–K, N–O ) closely conforms to the neotype of this species in terms of shell shape, size and colouration (for comparison with the type material, see Boeters & Falkner (2017: fig. 9) or Eschner et al. (2020: fig. 1t )). Based on our morphological and previous phylogenetic results ( Miller et al. 2022), we suggest that several populations previously assigned to other species of Mercuria should now be considered as members of M. similis (see discussion), which increases the known geographic range and intraspecific variation of this species. The species’ moderate shell variation can be observed across its geographic range ( Figs 1 , 4 ). However, the PCA displayed all populations identified as M. similis in proximity, suggesting a low level of intraspecific variation in shell shape. Most of the variation is attributed to differences in colour pattern and shell size. Although some individuals are orangish-brown [e.g., those from the La Cañada Stream (MNCN 15.05/94770), stream feeding Galayo’s Pond (MNCN 15.05/94771), the stream in Peralta de la Sal (MNCN 15.05/94774) and the Arc River near Les Cabanes (MNCN 15.05/94790), Fig. 4B–C, G, N ] the majority of the specimens have a whitish-grey periostracum. Another character that affects the perception of shell colour is the colouration of the epithelium. Most specimens have a darkly pigmented epithelium, though a few have an unpigmented epithelium [e.g., individuals from Barranco del Agua Salada (MNCN 15.05/94772), Fig. 4E ]. Unpigmented individuals were found cohabiting with pigmented ones in MNCN 15.05/94772. Additionally, the species presents moderate variability in shell size both within and among populations (Supp. file 2: Table S2), varying from 3.00– 4.84 mm, although larger specimens (5.4–5.7 mm) were found in the saltings in Riba de Santiuste, Guadalajara (MNCN 15.05/94762). This variability is likely influenced by environmental factors, such as flow rate and turbidity ( Verhaegen et al. 2018), and by the relative age of the animal. Hydrobiids are generally univoltine (i.e., have one generation per year) and semelparous (i.e., breed only once in a lifetime). In the case of the population from Riba de Santiuste, we found animals from a previous generation living together with adults from the current one. The older specimens (i.e., those with a greater number of whorls) collected from this population were indeed the larger-sized adults.

Major anatomical differences are observed in penis features, with three penis morphotypes found in the populations examined: 1-distal end of the penis longer than the penial appendix ( Fig. 7A–B ), 2-distal end of the penis and penial appendix about the same length ( Fig. 7C ), 3-distal end of the penis shorter than the penial appendix ( Fig. 7E–F ). This variation was observed within individual populations and thus does not correspond with any geographic distribution pattern. Holyoak et al. (2017) described the same phenomenon for M. tachoensis . These authors attributed the variation to allometric changes in the sexual maturity of the animals that occur during the reproductive season. Boulaassafer et al. (2018) found high variability of penis features in parasitized specimens of M. tensiftensis . Nevertheless, in our case, none of the specimens of M. similis dissected were parasitized.

Mercuria similis can be distinguished from the phylogenetically closest species M. egarensis sp. nov. and M. carrillorum sp. nov. by its larger, more globose shell ( Fig. 3 ). It can be distinguished from the geographically closest species M. balearica by its larger, more globose shell and also its slightly smaller, often pigmented, penial appendix and from M. tachoensis by its distant geographic distribution ( M. tachoensis lives in Atlantic coastal zones, whereas M. similis inhabits Mediterranean areas), granulated protoconch microsculpture and radula, which present one cusp less on the central and lateral teeth.

Figures

Fig. 4. Intraspecific variation of the shell shape and colour of Mercuria similis (Draparnaud, 1805). A. Salaboreja Spring, Casa de Ves, Albacete, Spain. B. Salado Stream, Casa de Ves, Albacete, Spain. C. Galayo´s Pond, Fuentalbilla, Albacete, Spain. D. Stream in Barranco del Agua Salada, Gelsa, Zaragoza, Spain (pigmented animal). E. Stream in Barranco del Agua Salada, Gelsa, Zaragoza, Spain (unpigmented animal). F. Saltwater gully in Aguinaliu, Huesca, Spain. G. Stream in Peralta de la Sal, Huesca, Spain. H. Sosa River at Peralta de la Sal, Huesca, Spain. I. Fonte Dame, Salses-le- Château, Aude, France. J. Font d´Estramar, Salses-le-Château, Aude, France. K. Pond at La Palme, Aude, France. L. Estany de la Ricarda, El Prat de Llobregat, Barcelona, Spain. M. Ullals de Baltasar, Amposta, Tarragona, Spain. N. Arc River near Les Cabanes, Bouches-du-Rhône, France. O. La Fouxde-Draguignan, France. P–Q. Arc River near Les Cabanes, Bouches-du-Rhône, France. P. Operculum, inner side. Q. Operculum, outer side.

Fig. 5. Shell and radula of Mercuria similis (Draparnaud, 1805) from Étang de Berre, Bouches-du- Rhône, France. A. Apical view of the shell. B. Details of the protoconch. C. Protoconch microsculpture. D. General view of the radular ribbon. E. Central, lateral, inner marginal and outer marginal teeth. F. Detailed view of the inner marginal teeth.

Fig. 6. Anatomy of Mercuria similis (Draparnaud, 1805). A–D. Female genitalia. A. Font Dame Spring, Salses-le-Château, Languedoc-Roussillon, France. B–C. Galayo´s Pond, Fuentalbilla, Albacete, Spain. D. Pond in La Palme, Languedoc-Roussillon, France. E–G. Arc River near Les Cabanes, Bouches-du- Rhône, France. E. Ctenidium and osphradium. F. Stomach. G. Perioesophageal ring.

Fig. 7. Male genitalia of Mercuria similis (Draparnaud, 1805). A–E. Penis. F. Penis and head. G–H. Prostate gland. A. La Cañada Stream. B. Font d´Estramar Spring. C. Fonte Dame Spring. D. Pond in La Palme. E. Barranco de las Negras. F. Stream crossing the town of Peralta de la Sal. G. Saltings of Riba de Santiuste, Guadalajara. H. Font d´Estramar Spring.

Fig. 1. Phylogenetic clustering and geographic location of the studied populations of Mercuria Boeters, 1971 throughout the western Palaearctic region. The tree topology on the left has been modified from Miller et al. (2022) to show the species clades (i.e., coloured clades) of the populations described here. One population (grey dot) represents the distribution of M. maceana (Paladilhe, 1869). Scale bar below topology: expected change per site.

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.