Identification of Physidae 1) Right- handed shells of various shapes: ovate, ovate-conical, spherical or quasi-spherical, outline elongate, asymmetrical, apex pointed................................................................................ – (Lymnaeidae). - Left-handed shells, spindle-shaped or ovoid-shaped, smooth and thin, pointed spire, small to medium-sized, 5–17 mm. Shells rather transparent, thin, corneous with a relatively large and long aperture without operculum.... – Physidae (Fig. 1, Tab. 2). Physidae Genus Key 1. Shell narrow, long, smooth, usually very glossy. Body shines through the shell. Mostly found in ephemeral (astatic) water bodies................................................................... – Genus - Aplexa (Fig. 1b, Tab. 1). - Spire of the shell is relatively blunt and short. Rather smooth surface of the shell or with very delicate spiral lines. Snails commonly occur in ponds, rivers and streams................................. – Genus Physa (Fig. 1a, c, d; Tab. 1). Physidae Species Key 1. Shell tall, slender, narrow, usually very glossy, semi-transparent (Fig. 1b), with a high spire (Fig. 1, 2b), height of the aperture about half of overall height of the shell (Fig. 3a). Aperture narrow, its external part sharp with a lip visible under SEM (Fig. 3c). Left-handed, spindle-shape. Body whorl not especially large and narrowed at bottom. The body of the snail usually black and does not overlap outside of shell. Umbilicus completely covered (Fig. 3a). The shell measures up to 13 mm x 6 mm, usually 8–15 x 3–6 mm with up to 7 whorls (usually 5.5–6), regularly increasing. Species occurs in almost all over Europe, often found in ponds, ditches, forest water bodies and other types of lentic habitats that are temporary, dried out, or have a high fluctuation in the water level (Tab. 1, Fig. 4)........................– Moss Bladder Snail – Aplexa hypnorum (Fig. 1; Fig. 2a–c). Reproductive anatomy: Penis has no preputial gland and a one-part glandular sheath. Penial sheath shorter than the preputium, widest in the distal part, tapering gradually to the distal end, which lacks a papilla. At the proximal end, the sheath is not sharply set off from the vas deferens and enlarges gradually (Starobogatov et al. 1989; Taylor 2003). - Shell shorter and more rounded, the height of the aperture at least two thirds of the overall height of the shell. The body of the snail pale brown or greenish. The hell up to 18mm x 11mm, with up to 4 whorls..................................– 2 2. Shell usually fragile, very delicate, thin, wide, glossy and translucent. The hell shape oval in outline (Figs 1c, 5). Spire short or very short, apex of the shell rounded (Fig. 2c). Spire blunted. 3–4 whorls (Fig. 1c, Fig. 5). Aperture high, tapering in adapical direction. Umbilicus covered. Body whorl inflated (Fig. 5). Sutural belts of shell very delicate, visible under SEM (Fig. 5b, c). Shell not larger than 12 mm x 8 mm, usually less than 10 mm, with 4 whorls. Species occurs all over Western and Central Europe in lentic habitats, slow-flowing waters, among detritus, at a wide range of pH (Tab. 1, Fig. 4).................................................................................. – Common Bladder Snail – Physa fontinalis Reproductive anatomy: Penial sheath consists of one glandular part. Bulky penial sac tapers from the wide proximal end to about 1/10 of its length, and enlarges before entering the preputium. Penial sac is longer than preputium. Penis is flagelliform, with a lanceolate stylet. The length of the vas deferens IV accounts for about 1/2 the length of the penial sac and preputium (Taylor 2003; Glöer 2019). - Shell thicker, rather strong, larger, spire pointed and higher, shell surface smooth.................................– 3 3. Shell often thicker, stronger and more opaque than in P. fontinalis, ovate and relatively wide (Fig. 1a). Spire pointed (1/3 shell height adult and less than 1/ 3 in juvenile specimens) (Figs 1a, 2a). Body whorl distinctly inflated. Aperture large, tapered in adapical part. Internal white lip at the aperture margin with characteristic thickening visible under scanning electron microscope (Fig. 6b, c). Umbilicus covered and sometimes a narrow fissure is visible. Shell corneous, with delicate shining. Shell commonly larger than in other Physidae, measuring up to 18 mm x 11 mm (usually 8–16 x 5–10 mm), up to 6 whorls (usually 5–6). Species occur in most parts of Europe (Fig. 4). Usually found in natural water bodies, in lakes, ponds, rivers, streams, ditches, or anthropogenic water bodies; tolerates higher water temperature, high level of pollution; may be present in degraded water environments (sewage, toxic waters, in high pH values e.g., 9.4) (Tab. 1)........ – American Bladder Snail – Physa acuta Reproductive anatomy: Penis with preputial gland and one-part muscular penial sheath, unipartite and not pigmented (Wethington 2004; Piechocki & Wawrzyniak-Wydrowska 2016; Maansi & Wats 2018). - Shell larger than 20 mm, relatively strong, deep horn-coloured and has shallow sutures (Fig. 7a), apex is broader and blunter than in P. acuta (Fig. 2d). Body pigmentation has clusters of large white pigment spots, upper whorls with reddish hue. The number of whorls 3–5; whorls rather convex, with the last whorl predominating (Fig. 1d); aperture accounts for 55–75 % of shell height, with a broad white callus on parietal side (Fig. 1d and Fig. 7b–g, i). Shape and size of aperture variable. Characteristic thickened visible under scanning electron microscopy (Fig. 7e, f, h). Species occurs in standing and slowly flowing waters, inhabiting permanent and temporary ponds, shallow inshore areas and marshes. It occurs on aquatic plants and organic matter, under stones on shallow gravelly foreshores and tolerates organic water pollution and eutrophic or hypertrophic conditions (Tab. 1). The current geographical range of this species is shown in Fig. 4 ..................... – Physa gyrina Reproductive anatomy: Preputial gland has a two-part penial sheath (glandular and muscular). The two sheaths are almost equal in size (Wenthington 2004).

Published as part of Cieplok, Anna, Anderson, Roy, Gawlak, Magdalena, Kałuski, Tomasz & Spyra, Aneta, 2022, Morphological diversification of alien and native aquatic snails of the genus Physa and Aplexa (Gastropoda: Physidae) of Western and Central European range, pp. 101-118 in Zootaxa 5168 (2) on pages 103-104, DOI: 10.11646/zootaxa.5168.2.1, http://zenodo.org/record/6876950