Research Article |
Corresponding author: Barna Páll-Gergely ( pallgergely2@gmail.com ) Academic editor: Edmund Gittenberger
© 2016 Barna Páll-Gergely, Takahiro Asami.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Páll-Gergely B, Asami T (2016) A new species of Gudeodiscus Páll-Gergely, 2013 from China, with extraordinary conchological and anatomical features (Gastropoda, Pulmonata, Plectopylidae). ZooKeys 564: 1-19. https://doi.org/10.3897/zookeys.564.6560
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A new species of the Plectopylidae, Gudeodiscus longiplica is described from northern Guangxi Province, southern China. The shell, anatomical and radular characters are figured and described. This new species is characterized by long plicae on its parietal shell wall, which have not been observed in any other Gudeodiscus species. In contrast, the long parietal plicae are characteristic for the genera Plectopylis and Chersaecia, which mainly inhabit Thailand and Myanmar. These two genera are, however, only distantly related to the new species, as other characters (anatomy, protoconch sculpture, parietal plicae) suggest. The male portion of the genital structure of the new species is characterized by two separate penial caeca with different lengths, but similar in outer and inner structure. The relevance of this anatomical character is discussed. Gudeodiscus longiplica sp. n. occurs sympatrically with Gudeodiscus soosi Páll-Gergely, 2013. The anatomy and radula characters of the latter species are also described and figured.
Taxonomy, systematics, anatomy, sympatric species, duplicated organ, plesiomorphic character
The Plectopylidae are composed of flat-shelled terrestrial snail species which are characterized by a complex, internal armature structure. The armature is composed of plicae (horizontal structures) and lamellae (vertical structures) on both the palatal and parietal sides of the body whorl. These barriers are situated ¼ – ½ whorl behind the aperture, thus, usually not visible from the aperture. Instead, the palatal plicae can be seen through the semi-transparent shell wall, whereas small holes must be made in the shell at appropriate sites to examine the parietal plication. The morphology of these plicae and lamellae serve as primary diagnostic characters for species recognition and identification. In addition to these peculiar conchological features, unique traits in the anatomy of Plectopylidae have been reported, i.e. “disposable” calcareous, hook-like granules inside the penis lumen which are probably spent during mating (
The most speciose genus in the Plectopylidae is Gudeodiscus Páll-Gergely, 2013, mainly distributed in the Chinese Guangxi Province and northern Vietnam, but some species have been reported from eastern Yunnan, southern Hunan and southern Guangdong provinces. More than half of the recorded 24 species of Gudeodiscus are known from only empty shells at this time (
Determination of number of shell whorls (precision to 0.25 whorl) follows
JUO Collection Jamen Uiriamu Otani (Koka, Japan)
OK Collection Kenji Ohara, Nishinomiya Shell Museum (Nishinomiya, Japan)
PGB Collection Barna Páll-Gergely (Mosonmagyaróvár, Hungary)
2013 Gudeodiscus Páll-Gergely, In: Páll-Gergely & Hunyadi, Archiv für Molluskenkunde 142(1): 4, 8.
Plectopylis phlyaria Mabille, 1887, by original designation.
2015 Gudeodiscus (Gudeodiscus), — Páll-Gergely, et al., ZooKeys 473: 13.
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,
(Figs
Nomenclature of the parietal plicae and lamellae of Gudeodiscus Páll-Gergely, 2013 (A–C) and Endothyrella Zilch, 1960 (D). A Gudeodiscus longiplica sp. n. B Gudeodiscus emigrans quadrilamellatus Páll-Gergely, 2013 C Gudeodiscus phlyarius (Mabille, 1887) D Endothyrella sp. Abbreviations: af: apertural fold; al: anterior lamella; ip: intermediate plica; lp: lower plica; map: main plica; mp: middle plicae; pd: posterior denticle; pl: posterior lamella; up: upper plica. In order to make the comparison easier, all figures show a dextral specimen (D is reversed). After
Shells of sympatric Chinese Gudeodiscus Páll-Gergely, 2013 species. A–E holotype of Gudeodiscus (Gudeodiscus) longiplica sp. n. F–JGudeodiscus (Gudeodiscus) soosi Páll-Gergely, 2013, shell from the type locality (coll. JUO). Figures C and H were taken after they have been opened in order to observe the inner plicae. Scale bar: 5 mm.
Protoconch (A, D) and teleoconch sculpture (B–C, E–F) of sympatric Chinese Gudeodiscus Páll-Gergely, 2013 species. A–C holotype of Gudeodiscus (Gudeodiscus) longiplica sp. n. D–FGudeodiscus (Gudeodiscus) soosi Páll-Gergely, 2013, shell from the type locality (coll. JUO) B and E shows the last and penultimate whorls opposite of the aperture C and F shows the last and penultimate whorls near the aperture.
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.
(in mm). D = 11.7, H = 4.6 (holotype); D = 10.3–12.2, H = 4.3–5.0 (paratypes, n = 5).
(Figs
Opened penis and larger caecum of Gudeodiscus (Gudeodiscus) longiplica sp. n. (A) and Gudeodiscus (Gudeodiscus) soosi Páll-Gergely, 2013 (B). Abbreviations: C: penial caecum; C1: larger penial caecum; C2: smaller penial caecum; Cp: papilla on the inner wall of the larger penial caecum; E: epiphallus; P: penis; Pp: pockets on the penis wall; Rm: retractor muscle. Note that the most proximal portion of the penis is not shown on the left figure.
(Fig.
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 G. 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 (
This new species is named for its long plicae on the parietal wall.
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.
Gudeodiscus longiplica sp. n. is known only from the type locality.
2013 Gudeodiscus soosi Páll-Gergely, In: Páll-Gergely & Hunyadi, Archiv für Molluskenkunde 142(1): 31–32, figs 42a–b, 66.
(Figs
One of the specimens was aphallic, i.e. the male part of the genitalia was entirely missing. The right ommatophoral retractor passes between the penis and the vagina of the second specimen. Atrium extremely short, slender, long; penis moderately long, spindle shaped; inner wall of the penis with approx. 14 low longitudinal folds which join each other in the direction of the atrium resulting in fewer number of folds posteriorly; on the penial wall of the apical part of the penis there are slit-like “pockets” arranged in a transversal row; no calcareous granules have been found inside these pockets; the penial caecum is situated on the apical portion of the penis, it is approx. one third of the length of the penis; its inner wall is ornamented with several rhomboid papillae with holes in the middle of each papillae; no calcareous granules were found in them; retractor muscle inserts on the apical part of the penial caecum; retractor muscle very long, branched off from the columellar muscle; epiphallus enters penis laterally, at the joint of the penis and the larger penial caecum; its inner wall with three strong longitudinal folds; vagina slightly longer and thicker than the penis; the inner wall of the vagina is with irregular, low, longitudinal folds; the bursa copulatrix starts on the proximal part of the vagina; its base is not thickened; the stalk is slender and very long, the bursa is oval, more thickened than in the other species; diverticulum starts at the end of the vagina, therefore the base of the diverticulum and the base of the bursa copulatrix are very far from each other; diverticulum very slender, without thickening at it end; it is approximately as long as the bursa copulatrix; spermoviduct contained several developing eggs.
(Fig.
See under Gudeodiscus longiplica sp. n.
We cannot rule out the possibility that the aphallic individual was a hybrid (see
Gudeodiscus soosi and Gudeodiscus longiplica sp. n. share an anatomical character that differentiate them from all other anatomically-known species of the Plectopylidae, including Gudeodiscus. The origination sites of the bursa copulatrix and the diverticulum are distantly situated from each other because the bursa copulatrix of both species branches off the vagina at approximately the middle vaginal section. In contrast, in all other members of Plectopylidae the bursa copulatrix and the diverticulum originate very near each other with both attaching at the proximal end of the vagina. This, however, does not warrant a genus-group-level distinction of Gudeodiscus longiplica sp. n. and G. soosi from other plectopylids. The general shell characters and the inner morphology of the penis (presence of a transversal row of slit-like “pockets”) places these two species in the genus Gudeodiscus. Furthermore, the retractor muscle inserts at the end of the penial caecum without additional curtain-like muscle fibres (characteristic for the subgenus Veludiscus Páll-Gergely, 2015) on the apical part of the penis. This trait places Gudeodiscus longiplica sp. n. and G. soosi in the subgenus Gudeodiscus (Gudeodiscus). The morphology of radular teeth also agrees with the other members of the subgenus Gudeodiscus. Namely, the central tooth is as large as the ectocone of the first laterals, the marginals are tricuspid or even quadricuspid with rather pointed inner cusp, and there is a deep incision between the two inner cusps. In contrast, Gudeodiscus (Veludiscus) species are characterized by central teeth smaller than the ectocone of the first laterals, and the inner cusps of the marginals are rather blunt with shallow incision between the two innermost cusps.
Gudeodiscus longiplica sp. n. has two surprising characters that need further discussion. Firstly, the two long, anteriorly-elongated parietal plicae that are in contact with the anterior lamellae, and secondly, its two separate penial caeca, which are similar in inner and outer morphology, but differ in size.
Gudeodiscus, Halongella Páll-Gergely, 2015, Sicradiscus Páll-Gergely, 2013 and Sinicola Gude, 1899 are known as genera lacking long horizontal parietal plicae on the parietal wall. Species belonging to these four genera possess two vertical lamellae (Fig.
Parietal plication of Plectopylidae species (diagrammatic figures). A Plectopylis leucochila Gude, 1898 (after
Both anatomically examined specimens of Gudeodiscus longiplica sp. n. had two separate penial caeca, both having their own fascicle of retractor muscle. The two caeca were different in length but the outer appearance and the inner structure were similar. The same anatomical trait in both specimens suggests that the two caeca are characteristic for the species and do not represent rare teratological event. No other members of the Plectopylidae are known to have two separate penial caeca. Moreover, as our non-exhaustive literature survey shows, the duplication of the penial caecum (or any accessory organ in similar relative positions) is a very rare event in stylommatophoran snails.
Two genera of the Cerastidae (= Pachnodidae; superfamily Enoidea), namely Altenaia Zilch, 1972 and Archeorachis Schileyko, 1998 possess two penial caeca arising from the apical part of the penis. None of these caeca have retractor muscles. One caeca is slender, vermiform, and the other is conic or ovate. Other genera of the Pachnodidae are known to possess only one type of the penial caeca, either vermiform or thick and fleshy (
In the literature we encountered some reports of retractor muscles with two branches, each of them inserting on the two penial caeca, or the penial caecum and the penis itself. Furcopenis darioi Castillejo & Wiktor, 1983, (Agriolimacidae) has a bifurcate “accessory organ” with retractor muscles inserting on both tips of the accessory body (
In most Gudeodiscus species the penis has larger pockets for calcareous hook-like granules than the penial caecum. In some examples the caecum was absent (
We are very grateful to Jamen William Otani and Kenji Ohara for providing us the study material. We are indebted to Bernhard Hausdorf, John Hutchinson, Heike Reise and Anatoly Schileyko for their help in evaluating the relevance of certain anatomical features and to Kurt Auffenberg for his help in correcting the English. We are also grateful for Menno Schilthuizen for his comments on the manuscript. This study was supported by Grants-in-Aid for Scientific Research (KAKENHI) from Japan Society for the Promotion of Science to T. Asami. Barna Páll-Gergely is an International Research Fellow of the Japan Society for the Promotion of Science.