Biserta putealis, Khalloufi & Béjaoui & Delicado, 2020

Khalloufi, Noureddine, Béjaoui, Mustapha & Delicado, Diana, 2020, Two new genera and three new subterranean species of Hydrobiidae (Caenogastropoda: Truncatelloidea) from Tunisia, European Journal of Taxonomy 648 (648), pp. 1-27 : 18-20

Biserta putealis gen. et sp. nov.

urn:lsid:zoobank.org:act:AB67B9A3-8BA6-4AC2-97E3-97C61E6A4C32

Figs 7–8

Diagnosis

Shell 1.6 to 2.0 mm high, elongate-conic, brown-yellowish; central radular tooth formula (5)4–C– 4(5)/1–1; bursa copulatrix pyriform, with a short duct; two seminal receptacles, SR1 more developed and pedunculated, SR2 small, globular, located near loop before the pouch; prostate gland bean shaped, ovate in section, folded; penis gradually tapering, unpigmented, with two sessile lobes closely positioned to one another. Distinguished from other closely related species by>8.0% for COI.

Etymology

The species epithet is from the Latin adjective ‘ putealis ’, meaning ‘from a well’.

Type material

Holotype

TUNISIA • 1 spec. (sex unknown, preserved in ethanol 80%); Bizerte Province, 7 km south of Menzel Bourguiba, Soudene Well ; 37.09046º N, 9.777997º E; 115 m a.s.l.; 15 Mar. 2015; N. Khalloufi leg.; MNCN 15.05/200099H.

Paratypes

TUNISIA • 5 specs (preserved in ethanol 80%); same collection data as for holotype; MNCN 15.05/200099P • 32 specs (preserved in ethanol 80%, 2 ♀♀, 2 ♂♂ dissected and 2 specs processed for DNA sequencing); same collection data as for holotype; UGSB 17664 • 70 specs (preserved in ethanol 95%, ca 40 individuals dissected); same collection data as for holotype; Khalloufi’s collection .

Type locality

TUNISIA: Bizerte Province, 7 km south of Menzel Bourguiba, Soudene Well; 37.09046º N, 9.777997º E; 115 m a.s.l.

Description

MEASUREMENTS. Holotype: SL = 2.00 mm, SW = 1.04 mm, SL/SW = 1.92, AH = 0.98 mm, SL-LBW = 0.70 mm, WBW = 0.97 mm, AL = 0.93 mm, AW = 0.70 mm, WPW = 0.78 mm, WAW = 0.17 mm.

SHELL. Elongate-conic, brown to yellowish, with 4–4.5 whorls ( Fig. 7 A–D; Table 2). Protoconch ( Fig. 7G ) obtuse, near planispiral, about 1.25 whorls, diameter about 300 µm; protoconch microsculpture granulated. Teleoconch whorls convex, separated by deep sutures; body whorl occupying ¾ of total shell length. Aperture about 50% of total shell length, pyriform, slightly angled on the top and narrowly disjunct from parietal wall of body whorl; inner lip thin but thicker than outer lip; peristome margin ( Fig. 7B ) straight. Umbilicus narrow and closed by inner lip.

OPERCULUM. As for genus, thin, flat, whitish (nuclear region slightly yellowish), with ca 2 whorls ( Fig. 7 E–F); attachment scar area oval and located near nucleus.

RADULA. Length intermediate (25% total maximum shell length), having about 80 rows of teeth. Central tooth ( Fig. 7 H–I) formula (5)4–C–4(5)/1–1, cutting edge strongly concave; basal tooth face M-shaped and relatively narrow wings; basal tongue broadly V-shaped, about equal to lateral margins; a single small pair of basal cusps, triangular. Lateral teeth ( Fig. 7H ) formula (4)3–C–5(6); central cusp large, narrow, pointed. Inner marginal teeth having 23–25 sharp cusps. Outer marginal teeth having 22–23 sharp cusps ( Fig. 7J ).

PIGMENTATION AND ANATOMY. Visceral coil brown-yellowish, showing by transparency the gonad; pallial coil with uniform and dense pigmentation on the roof, anteriorly to edge of mantle, foot and area between tentacles ( Fig. 8C ). Black small eyes surrounded by brownish pigment. Snout with medium distal lobation. Tentacles parallel-side, distal end nonexpanded. Ctenidium filaments about 13, small, taller than wide. Osphradium whitish, ellipsoidal, positioned centrally along ctenidium ( Fig. 8A ). Stomach slightly longer than wide with a small gastric (posterior) caecum ( Fig. 8B ); rectum wide, folded and S-shaped.

MALE GENITALIA. Penis gradually tapering ( Fig. 8D ), medium sized, unpigmented, slightly folded; filament short, tapering; basal portion intermediate in width, shorter than distal portion, attached centrally to the head well behind the eyes; penis having two developed lobes, very close to one another on opposite sides of penis; both lobes having distal papilla and showing by transparency tubular glands; ventral lobe large, pyriform, pedunculated; dorsal lobe small, pyriform, sessile. Prostate gland small, close, beanshaped, longer than wide (0.25 mm / 0.05 mm). Posterior vas deferens with several loops, yellowish and developed in its median portion (about 2 mm in length and 0.05 mm in section). Pallial vas deferens straight, narrow, whitish, unciliated, entering the posteroventral portion of gland and exiting from its anterior end.

FEMALE GENITALIA. Ovary simple, with stalked lobes, occupying near 40% of visceral coil. Distal female genitalia occupying near 50% of pallial roof; albumen gland approximately as long as capsule gland ( Fig. 8E ). Bursa copulatrix pyriform, having a shorter duct than bursal length. Renal oviduct unpigmented, coiled, having a spherical pouch at the end of the coiled section. Two seminal receptacles; SR1 medium sized, elongate, pedunculate, joining renal oviduct just above the insertion point with bursal duct; SR2 small, globular, sessile, located on renal oviduct near loop before pouch ( Fig. 8 F–G).

Ecology and distribution

This species was found only in a small well in southern Menzel Bourguiba city, northern Tunisia. The well is 1.5 m in diameter and 4 m deep. Specimens were very abundant on the rock walls and on the rocky and sandy bottom. Water salinity was about 1.5 ppt. Pseudamnicola sp. was the only co-occurring gastropod species.

Remarks

Some individuals of the collected population lack body pigmentation ( Fig. 7C ), which could indicate adaptation to subterranean conditions (Delicado 2018). Other anatomical structures resembled those of the pigmented individuals.

Figures

Fig. 7. Shells, opercula and radulae, Biserta putealis gen. et sp. nov. A–D. Shells. A–B. Holotype, MNCN 15.05/200099H. C–D. Paratypes, MNCN 15.05/200099P. E–F. Operculum (E = inner side; F = outer side). G. Detailed microsculpture of protoconch. H–J. Radulae. H. Portion of radula ribbon. I. Central radular teeth. J. Marginal teeth.

Fig. 8. Anatomy of Biserta putealis gen. et sp. nov. (paratypes, UGSB 17664). A. Ctenidium and osphradium. B. Stomach. C. Head of male and penis. D. Detail of penis and penis lobes. E. Pallial oviduct. F. Bursa copulatrix and seminal receptacles. G. Ditto, observed by transmitted light. Anatomical abbreviations explained in the text.