Lindholmiola Hesse, 1931

Subai, Peter & Neubert, Eike, 2014, Revision of the genus Lindholmiola HESSE, 1931 (Gastropoda: Pulmonata: Helicodontidae), Contributions to Natural History 23, pp. 1-94 : 3-5

Lindholmiola Hesse, 1931

1931 Lindholmiola HESSE , Zoologica, 18: 50 [type species by original designation Helix lens A. FéRUSSAC, 1832 ].

Description: shell flat to lentiform (H: 3.1–7.5 mm, D: 7.2–16.5 mm); spire slightly elevated (exception: L. gyria with a concave spire); colour brown to yellowish-brown; teleoconch surface usually with hairs; teleoconch sculpture of fine to coarse radial riblets; whorls regularly increasing, 5¼–7¾ whorls; periphery of last whorl rounded, bluntly shouldered or sharply keeled; last whorl strongly bends downwards before reaching the aperture; umbilicus narrow to moderately wide, cylindrical to perspective, usually only slightly covered by the peristome (exception: L. barbata , where the umbilicus is almost completely covered); aperture narrow, oblique and curved (in lateral view); peristome narrow to broad, reflexed.

Genital organs ( Fig. 1 ) simple; atrium short; penis a club-shaped tube, epiphallus distally strongly contracted (often, this area is covered by a glandular tissue); penial retractor muscle attaching at the central part of epiphallus, which connects to vas deferens without any visible distinction; vagina short (completely reduced in L. reischuetzi ); glandula a single tube with a narrow stem and a broader hose often sculptured by crossing furrows; bursa copulatrix with a narrow pedunculus and a more broadened vesicle (often not clearly visible) (Schileyko 2006: 1919, Fig. 2439).

Interior of the terminal genital organs with a long fold starting at the genital pore and ending at the distal vagina; atrial part of the fold often subdivided by small crossing furrows (an additional semicircular crested fold in the atrium can be found in L. regisborisi ); characters of the penial lumen differ according to the species, usually with 2–3 raised longitudinal pilasters filling at least the distal half of the penial lumen (exception: In L. corcyrensis , the longitudinal pilasters are replaced by v-shaped, obliquely arranged, short folds).

It has to be stressed that the characters of the terminal genital organs as described above can only be seen in sexually mature specimens. In juveniles, the folds are missing or very weak.

Differentiating remarks: The shells of Helicodonta are also depressed but never lentiform and usually concave. In species of this genus, the whorls increase faster in width, particularly the ultimate and the penultimate whorl, which are always broader than those in Lindholmiola . Additionally, they are laterally rounded and only slightly shouldered. The umbilicus of Helicodonta spp. is broader and more perspective if compared to Lindholmiola , and their apertures have often three indentations which are even thickened to form teeth. The peristome is usually broadened to form a lip.

Both genera differ in the morphology of their genital organs: Helicodonta species have a considerably longer penis and vagina and a short tubular organ of unknown function that branches off distally to glandua and bursa copulatrix ( Fig. 2 ) (not present in Lindholmiola ). In the interior of the terminal genital organs, there are elongated narrow pilasters in the vagina (different in Lindholmiola ), and in the middle of the penis, the penial lumen is filled by two thickened pilasters (different in Lindholmiola ). In the distal part of the penis, an additional pilaster covered by small punctiform granules is found (not present in Lindholmiola ). The glandular tissue at the distal end of the epiphallus of Lindholmiola spp. is missing in Helicodonta species.

Figures

Figs. 1–2. Genital organs of Helicodontidae. Fig. 1: Lindholmiola barbata; Greece, Kríti, Nomos Haniá, Bay of Soúda, 100–150 m from the mouth of the river S of the English cemetery. Fig. 2: Helicodonta obvoluta (O. F. MüLLER, 1774); Belgium, valley of the Meuse, 500 m from Annevoie in direction to Dinant, 2a) situs of genital organs, 2b) interior structure of penis. — Abbreviations used for the description of the genital organs: A = atrium, Al = albumen gland, E = Epiphallus, G = distal glandular part of epiphallus, Gl = Glandula, Hd = hermaphroditic duct, Hg = hermaphroditic gland, P = Penis, R = retractor muscle, Sp = Spermoviduct, V = vesicle, Vag = Vagina, Vd = Vas deferens.