Gudeodiscus (Gudeodiscus) longiplica, Pall-Gergely, Barna & Asami, Takahiro, 2016

Pall-Gergely, Barna & Asami, Takahiro, 2016, A new species of Gudeodiscus Pall-Gergely, 2013 from China, with extraordinary conchological and anatomical features (Gastropoda, Pulmonata, Plectopylidae), ZooKeys 564, pp. 1-19 : 2-7

Gudeodiscus (Gudeodiscus) longiplica sp. n. Figures 2 A–E, 3 A–C, 4 A–C, 5, 7 A–B, 8A, 9 A–C, 10B

Material examined.

Guangxi (广西), Tiane Xian (天峨县), Liupai Zhen (六排鎮), Shuiliandong (水帘洞), 354 m, 25°00.623'N, 107°09.994'E, leg. Ishibe, T., Ohara, K., Okubo, K. & Otani, J. U., 21.10.2011, NHMUK 20150375 (holotype = shell + body in ethanol + radula on double-faced adhesive tape), NHMUK 20150376/1 paratype (= shell + body in ethanol), JUO/2 paratypes (= shells), PGB/1 paratype (= shell, ex coll. J.U. Otani); Same locality and collection data, OK/4 (= corroded paratypes; these four shells are paratypes of Gudeodiscus soosi as well).

Description of the shell

(Figs 2-4). The description is based on the holotype and a paratype (NHMUK 20150376) which was opened in order to examine the parietal plicae.

Shell small, dextral, corneous-light brown, translucent, nearly flat, only the protoconch is elevated; whorls 6.75; suture shallow at the protoconch but very deep, even groove-like, near the aperture; protoconch lighter in colour than the rest of the shell, 2 whorls; its surface very finely granulated, matt, and rather regularly ribbed near the suture, ribs becoming weak anteriorly; radial sculpture weakest on the protoconch and becoming stronger towards the end of the protoconch; the umbilical side of the protoconch is not ribbed, but finely granulated, matt; from dorsal view the first three whorls of the teleoconch are irregularly wrinkled, glossy, and lighter coloured than the rest of the shell; this sculpture changes gradually (after approx. 2.5 whorls) to a more strongly ribbed, somewhat darker, less glossy surface which possesses fine periostracal filaments on the ribs; these radial periostracal filaments are most prominent near the suture; the ribbed dorsal surface gradually changes to a smooth, glossy surface at the edge of the body whorl; umbilicus wide, funnel-shaped, shows all whorls; aperture slightly oblique to the shell axis, peristome white, moderately thickened and very much reflexed; parietal callus strong, elevated but rather blunt; it is angled when it joins the apertural fold; apertural fold long, but free from the main plica.

Parietal wall with two lamellae; the anterior is very much elevated, rather straight but oblique to the shell axis; its lower end is situated more anteriorly than the upper end; the posterior lamella is much weaker (lower) than the anterior, it is C-shaped; the two separate lamellae are well distinguishable, but they are connected to each other by a white calcareous layer; main horizontal plica long, it is connected to the upper end of the anterior lamella; the main plica almost reaches the apertural fold, but in both examined specimens the two structures are free from each other; lower plica long, starts from the lower end of the posterior lamella and ends before the ending point of the main plica; lower plica free from the anterior lamella in case of the holotype, but in the paratype there is a weak connection between them; middle plica strong, starts from the lowermost point of the anterior lamella, and ends in the same position as the lower plica. In case of the paratype there are some additional short plicae in contact with the other, above mentioned plicae, namely: one above the anterior end of the main plica, one above the middle plica, and one above the anterior end of the lower plica. Palatal wall with six plicae; the first is long, slender, it is situated near the suture; the second is situated in comparatively large distance from the first; the second plica is even longer than the first, its posterior part is curved downwards; the last (6th) plica is relatively short, with pointed anterior and blunt posterior ends; the middle plicae (3rd to 5th) are complicated, with a shape similar to curly brackets when looking through the semi-transparent shell wall; the anterior leg of the "curly brackets" are longer than the posterior ones; when observing from inside, the middle plicae have a triangular, pointed tip.

Measurements

(in mm). D = 11.7, H = 4.6 (holotype); D = 10.3-12.2, H = 4.3-5.0 (paratypes, n = 5).

Characters of the genital structure

(Figs 5, 7 A–B, 8A). Two specimens were anatomically examined. The right ommatophoral retractor passes between the penis and the vagina. Atrium slender, long; penis moderately long, with slimmer distal part; there are two penial caeca, both of them with their own retractor muscle which merge to a single fascicle after some distance; retractor muscle very long, branched off from the columellar muscle; one of the penial caeca is larger and slimmer than the other; the larger one is approximately half of the length of the penis; epiphallus enters penis laterally (at the meeting point of the penis and the larger penial caecum); penis internally with approximately 16 low, longitudinal folds; just distally from the joint of the epiphallus there is a single, straight, transversal row of small “pockets” which are formed by the longitudinal folds; we have not found calcareous objects in these pockets; larger penial caecum internally with a longitudinal, main row of rounded papillae; this main row consists of 8-9 papillae; there are other, smaller papillae arranged in 2-3 longitudinal rows on the inner wall; there are a few additional papillae adjacent to the ones of the main row; we have found a single calcareous granule with pointed tip and rounded, widened base in one of the papillae; the smaller penial caecum has a single, longitudinal row of papillae with approx. five papillae; the papillae are very well visible throughout the semi-transparent wall of the caeca; epiphallus as long as the longer penial caecum, internally with three longitudinal folds; vas deferens enters epiphallus apically, it is very slender, but gets thicker near the proximal portion of the vagina; vagina extremely long, approximately two times longer than the penis and the penial caecum combined; the distal part is very slender; the proximal portion is slightly thicker than the penis; the inner wall of the vagina is with irregular, low, longitudinal folds, which are the strongest at the proximal end of the vagina (closer to the joining point with the vas deferens); the bursa copulatrix starts a bit distally than the middle point of the proximal portion of the vagina; its base is thickened, but gets slimmer after a short distance; the stalk is slender and very long, the bursa is gradually thickened at the end; diverticulum starts at the end of the vagina, therefore the base of the diverticulum and the base of the bursa copulatrix are situated very far from each other; diverticulum very slender, without thickening at its end; it is approximately as long as the bursa copulatrix; a long, slender, glass-like, fragile spermatophore have been found in the diverticulum; spermoviduct very slender, long.

Characters of the radula

(Fig. 9 A–C). Radula elongated, but not very slender, central tooth present, laterals 7 or 8 (it is difficult to decide whether the 8th row belong to the laterals or the marginals), standing in straight lines (perpendicular to the central column); marginals approximately 11-12; marginals are placed in slightly oblique rows; central tooth wide-based triangular, smaller than the endocone of the first lateral, but approximately as large as the ectocone of the first laterals; laterals bicuspid, ecto cones triangular, endocones have rather parallel margins with triangular, pointed tip; marginals usually tricuspid (= the endocone has two cusps); occasionally the innermost cusp is also divided into two cusps resulting in three cusps of the structure equivalent to the endocone of the laterals; some of the external marginals have both the endocone and the ectocone divided into two cusps; all cusps pointed, the incision between the innermost two cusps (= two cusps of the endocone) is deep.

Differential diagnosis.

Gudeodiscus longiplica sp. n. differs from all other Gudeodiscus species by the morphology of the parietal plicae and lamellae, and the presence of two penial caeca. It differs from the sympatric Gudeodiscus soosi by the presence of two well-developed parietal lamellae and three horizontal plicae (main, lower, and middle), as well as the apertural fold ( longiplica sp. n.: long; soosi : short), the palatal plicae ( longiplica sp. n.: first two long; soosi : first very short, second moderately long), the shell shape ( longiplica sp. n.: dorsal side flat; soosi : dorsal side slightly domed) and the fine sculpture of the dorsal side ( longiplica sp. n.: several radial periostracal folds; soosi : nearly smooth).

The long parietal plicae of Gudeodiscus longiplica sp. n. is similar to those of some, mostly sinistral species of Chersaecia and Plectopylis , which inhabit north-eastern India, Myanmar, northern Thailand, and northern Malaysia. The anatomy of Plectopylis and Chersaecia is insufficiently known, therefore we cannot use the anatomical characters of Gudeodiscus longiplica sp. n. to reject a close relationship with Plectopylis and Chersaecia . Gudeodiscus longiplica sp. n. has a regularly ribbed protoconch, whereas Plectopylis and Chersaecia species have finely tuberculated or smooth embryonic whorls ( Schileyko 1999, Páll-Gergely et al. 2015b). Moreover, the palatal plicae of Chersaecia and Plectopylis are different (see Discussion).

Etymology.

This new species is named for its long plicae on the parietal wall.

Type locality.

Guangxi (广西), Tiane Xian (天峨县), Liupai Zhen (六排鎮), Shuiliandong (水帘洞), 354 m, 25°00.623'N, 107°09.994'E.

Distribution.

Gudeodiscus longiplica sp. n. is known only from the type locality.