Pseudamnicola megastomus Delicado, Khalloufi & Hauffe 2025, sp. nov.
Creators: name: Delicado, Diana
name: Boulaassafer, Khadija
name: Khalloufi, Noureddine
name: Hauffe, Torsten
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Littorinimorpha
Hydrobiidae
Pseudamnicola
Pseudamnicola megastomus

description: Pseudamnicola megastomus Delicado, Khalloufi & Hauffe sp. nov.
(Figs 11, 12)
Pseudamnicola sp. 2 — Delicado et al. 2015 [in part] Pseudamnicola sp. 2 — Delicado et al. 2018
Pseudamnicola sp. 2 — Boulaassafer et al. 2020
ZooBank registration: urn:lsid:zoobank.org:act: 0DD397BA-5997-4FF8-8E42-A3A4EB495D83
Etymology
From Greek megastome, referring to the large shell aperture of this species.
Type material
Holotype (MNCN 15.05 /200501H) and ~ 30 paratypes (MNCN 15.05 /200501P) in the MNCN collection. Type locality: Wedi El Garâa Stream, Bizerte, Tunisia.
Material studied
Wedi El Garâa Stream, Bizerte, Tunisia, 37.2426°N, 9.7185°E, leg. N.K. and D.D., May 2009, MNCN 15.05 /200501 (70% ethanol). A well in the Ennkhilet region, north of Ichkeul, Tunisia, 37.2055°N, 9.6677°E, leg. N.K. and D.D., May 2009, MNCN 15.05 /95107 (70% ethanol).
Diagnosis
Shell ovate-conic, with a relatively wide aperture (AW/AL ratio>.75); protoconch microsculpture pitted; central radular tooth formula (4)3-C-3(4)/1-1; bursa copulatrix large, pyriform, with a duct slightly longer than bursal length; SR1 elongate, with a short duct; penis large, gradually tapering, unpigmented, with many folds over the entire surface and a moderately wide base; nervous system darkly pigmented, elongate (mean RPG ratio =.52).
Description
Shell ovate-conic, whorls 4–4.5, height 3–4 mm (Fig. 11A, C, D; Supporting Information, Table S3). Periostracum yellowish. Protoconch ~450 µm wide, whorls 1.5; nucleus ~120 µm wide; protoconch microsculpture pitted (Fig. 11F). Teleoconch whorls moderately convex, with deep sutures; body whorl large, occupying about three-quarters of total shell length. Aperture almost as wide as long, slightly oval; inner lip thicker than outer lip; peristome margin simple, straight (Fig. 11B). Umbilicus narrow, not covered by the inner lip. Holotype: SL = 3.75 mm, SW = 2.75 mm, AL = 2.04 mm, and AW = 1.62 mm.
Operculum oval, brownish, about two and a half whorls; muscle attachment area oval and located near the nucleus (Fig. 11E).
Radular length intermediate, ~750 µm (~25% of total shell length), with ~55 rows of teeth (Fig. 11G). Central tooth formula (4)3-C-3(4)/1-1 (Fig. 11H); basal tongue V-shaped, length about equal to lateral margin. Lateral tooth formula 2-C-2 (rarely with three lateral cusps). Inner marginal teeth having 16–17 tapered cusps, shortening towards the base. Outer marginal teeth with ~22 sharp cusps (Fig. 11I).
Animal black-pigmented except for neck and tentacles (Fig. 12F). Snout as long as wide, with medium distal lobation; foot size intermediate, with dorsal pigmentation. Ctenidium with 16–19 well-developed gill filaments, occupying ~50% of pallial cavity length and posteriorly positioned. Osphradium of intermediate width and opposite middle of ctenidium (Fig. 12A). Stomach as long as wide, with two chambers almost equal in size and a medium-sized posterior caecum; style sac longer than wide, surrounded by an unpigmented intestine (Fig. 12B; Supporting Information, Table S4). Nervous system elongate (mean RPG ratio =.52), darkly pigmented, darker on ganglia than on connectives and commissures; cerebral ganglia approximately equal in size (Fig. 12C).
Female glandular oviduct approximately three times as long as wide. Albumen gland shorter than capsule gland. Bursa copulatrix pyriform, longer than wide. Bursal duct longer than bursal length. Renal oviduct black-pigmented until the insertion of seminal receptacle or the area above, relatively straight. Seminal receptacle elongate, with a short duct, joining renal oviduct at the insertion point with bursal duct (Fig. 12D, E; Supporting Information, Table S5).
Male genitalia with a prostate gland approximately three times as long as wide, bean-shaped; seminal duct entering the middle-posterior region; pallial vas deferens emerging close to its anterior edge (Fig. 12H). Penis longer than head, gradually tapering, unpigmented, with many folds over the entire surface (Fig. 12F, G; Supporting Information, Table S6); base narrower than central area of penis; attached well behind the right eye; penial duct narrow, curved, coursing close to outer edge.
Habitat
Known from two different habitat types in southern Bizerte. The species was found in the muddy bottom of a stream (Wedi El Garâa) near Bizerte and attached to the walls of a well in the Ennkhilet region north of Ichkeul. In the first locality, aquatic plants are sparse, and the water temperature and conductivity are 22°C and 2.6–2.9 mS, respectively. In the second locality, aquatic plants (Ranunculus sp. and Lemna minor Linn.) and filamentous algae (Spirogyra sp.) are dense. The temperature and conductivity of the water are high (24°C and 1.6–2.4 mS, respectively). Snails were found in low abundance at the two localities. Co-occurring mollusc species are Galba truncatula, Physella acuta, Gyraulus parvus (Say, 1817), and Pisidium sp.
Remarks
Pseudamnicola megastomus has an unusually large shell aperture, comparable to that of Pseudamnicola algeriensis Glöer, Bouzid & Boeters, 2010 (Glöer et al. 2010: fig. 14). However, specimens of P. megastomus are slightly smaller and have a narrower last body whorl and a wider aperture than in the latter species. Its shell morphology is similar to that of a paratype of Pseudamnicola ghamizii Glöer, Bouzid & Boeters, 2010 (Glöer et al. 2010: fig. 39), but differs in its higher shell and larger aperture. The species was recorded from north-eastern Tunisia, where another accepted species of Pseudamnicola, P. meluzzii, is distributed. The former can be distinguished easily by having a larger shell, a wider aperture, fewer cusps on the lateral and central radular teeth, and a longer bursa copulatrix. The features of the penis of both species are very similar. The newly discovered species in north-western Tunisia, P. araujoi, differs from P. megastomus in having a smaller and more globose shell, a shorter penis, and a less concentrated nervous system. Pseudamnicola megastomus and P. conovula were depicted as closely related species in previous studies (Delicado et al. 2015, 2018, Boulaassafer et al. 2020) and by all our phylogenetic analyses (Fig. 2; Supporting Information, Figs S4–S 6). However, this relationship has always
Gastropod species delimitation • 23 been poorly supported. A population of P. conovula living at Toute Stream (Bizerte Region) and its conspecific populations differ from P. megastomus according to their different shell features and female reproductive anatomy. The average sequence divergence among these four species was 2.5%–7.4% for COI.
description: Published as part of Delicado, Diana, Boulaassafer, Khadija, Khalloufi, Noureddine & Hauffe, Torsten, 2025, A holistic perspective on species delimitation outperforms all methods based on single data types in freshwater gastropods (Caenogastropoda: Hydrobiidae: Pseudamnicola), pp. 1-31 in Zoological Journal of the Linnean Society 203 (1) on pages 21-23, DOI: 10.1093/zoolinnean/zlae010, http://zenodo.org/record/14774861