Margarya, NEVILL, 1877

Zhang, Le-Jia, Chen, Shi-Chao, Yang, Li-Te, Jin, Lei & Köhler, Frank, 2015, Systematic revision of the freshwater snail Margarya Nevill, 1877 (Mollusca: Viviparidae) endemic to the ancient lakes of Yunnan, China, with description of new taxa, Zoological Journal of the Linnean Society 174 (4), pp. 760-800 : 765-769

MARGARYA NEVILL, 1877

Type species: Margarya melanioides Nevill, 1877 (original designation).

Taxonomic remarks

The genus Margarya was described by Nevill (1877) based on shells of the type species collected by A. R. Margary from Lake Erhai, the type locality of M. melanioides . Subsequently, further nominal species described from various lakes of surrounding areas on the Yunnan Plateau were attributed to this genus based on their similar shells; however, previous authors delimited species inconsistently. For example, Dautzenberg & Fischer (1905) treated all specific names introduced at the time as varieties of the type species, M. melanioides , whereas Yen (1939) treated them as subspecies. By contrast, Tchang & Tsi (1949) recognized seven distinct species, elevating M. mansuyi ,

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M. monodi , Margarya tropidophora ( Mabille, 1886) , and M. francheti to full species, and describing two new species, M. yangtsunghaiensis and M. elongata . In addition, they recognized two varieties, M. mansuyi var. bicostata and M. elongata var. yini . Based on the study of subfossil shells, Xia (1982) elevated the two varieties Margarya yini and Margarya carinata to full species and described a new subfossil species Margarya tchangsii . Huang (1986) described another fossil species from Well Can-I in Kunming, Margarya nana . Two additional fossil species from the Middle Pleistocene, Margarya spinicostata Li, 1987 and Margarya angulata Li, 1987 , were subsequently described from the Sheshan formation, Lijiang Basin, Western Yunnan. The first molecular phylogeny of Margarya was presented by Huang & Wang (2008) and Huang (2007), who also

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described Margarya melanioides dianchiensi s. The molecular phylogenetic study of Du et al. (2013) found the genus Margarya not to be monophyletic. Tian et al. (2013) described a fossil species, Margarya nanningensis , from the lower Oligocene of Nanning Basin, Guangxi, China, which is the first record of Margarya from outside of Yunnan. Based on conchological characters, He (2013) reviewed 14 species-group taxa of Margarya . Six species were retained as valid, and two subgenera of Margarya were described, viz. Mabillemargarya (for the type species M. francheti ) and Tchangmargarya (for the type species M. yangtsunghaiensis ).

Based on the phylogenetic relationships recovered herein, and in accordance with comparative morphology, we place Mabillemargarya into synonymy with Margarya , as M. melanioides and M. francheti are both members of the same phylogenetic clade and share key characteristics typical for this genus. Species of Margarya can best be differentiated from each other by the structure of the first four whorls of the shell (i.e. the mature juvenile shell period; Fig. 12 ). In addition, we separate Tchangmargarya as a distinct genus from Margarya . Two species previously assigned to Margarya , M. mansuyi and M. bicostata , are placed in the newly introduced genus Anularya gen. nov. (see below).

Description

Shell large, conical, up to 100 mm tall, thick, solid, mostly with seven whorls, including two protoconch whorls, with well-developed subsutural ramp or depression at upper portion of each whorl, except the protoconch; whorls generally with between three and five prominent spiral keels, each supporting a row of nodules, spines, or wave-like protuberances at lower whorls, sometimes only having smooth keels, lower keel always covered by suture, thus nearly invisible on spiral whorls; three or four rather weak spiral ribs extending onto umbilical area; aperture ovate; umbilicus small or absent.

Operculum corneous, ovate, rather thin, reddish or yellowish brown, with subcentral nucleus and concentric growth lines; nucleus large, with grains or veins; opercular scar large, relatively rough, outside smooth, thickened; operculum almost as large as aperture.

Radula with about 100–130 rows of teeth, each row with one central tooth plus one lateral tooth and two marginal teeth on either side of it; outer marginal teeth with between ten and 14 denticles.

Body and mantle colour of living animals white or grey, with fine dense yellow or orange pigment spots ( Fig. 7A–D ). Foot comparatively small, with large opercular lobe, cephalic tentacles about 8–10 mm in length, right tentacle thickened in males, modified into a penis ( Fig. 7G ). Gonochoristic, prostate in males yellow, about 20 mm long, testis pale brown to yellow. Gravid females retaining between two and eight juveniles under different developing period in uterus, size at birth usually exceeding 10 mm.

Comparative remarks

Margarya differs from most other viviparid genera by its larger size, thicker shell, ramp-like shoulder on upper section of whorls, spiral keels on shell, a large opercular scar, and a granulated nucleus of the operculum. It differs from Anularya gen. nov. and Tchangmargarya in its umbilical sculpture, having several weak spiral ribs. Species of Tchangmargarya have two welldeveloped, nodular spiral ribs, whereas Anularya species have no spiral umbilical ribs ( Fig. 6 ). It also differs from these two genera by having a large operculum with granulated nucleus ( Fig. 8 ). In mature individuals, the operculum of Tchangmargarya and Anularya species is generally smaller than that of Margarya species (P <0.0001), whereas Anularya has a larger opercular scar than all other genera (P <0.0001), and Cipangopaludina has the smallest opercular scar ( Fig. 9 ). Acanthotropis partelloi Bartsch, 1909 , an endemic species of Lake Lanao, Mindanao, Philippines, has a similar, large, elongated and solid shell, with a spiral keel supporting a row of tubercles and spines above a suture of lower whorls. It differs, however, by lack of ramplike shoulder and absence of additional spiral ribs and smooth sculpture on early whorls. As for anatomic characters, Margarya closely resembles Cipangopaludina ; however, it differs by a smaller foot, larger opercular lobe, body and mantle colour, shorter cephalic tentacles, and colour and length of prostate.

Figures

Figure 6. Umbilical views of the shells: A, Margarya melanioides; B, Margarya monodi; C, Margarya francheti; D, Margarya oxytropoides; E, Tchangmargarya multilabiata sp. nov.; F, Tchangmargarya yangtsunghaiensis; G, Anularya bicostata; H, Anularya mansuyi. Margarya with several weak spiral ribs; Tchangmargarya with two strong nodular spiral ribs; Anularya gen. nov. without any sculpture.

Figure 7. Skin colour and morpholgy of cephalic tentacles: A, Margarya melanioides; B, Margarya francheti; C, Margarya oxytropoides; D, Margarya monodi; E, Tchangmargarya yangtsunghaiensis (offered by Jin Chen); F, Anularya bicostata; G, head of male Margarya species; H, head of male Tchangmargarya species; I, head of male Anularya species. Abbreviations: ey, eye; lt, left tentacle; pb, proboscis; pn, penis (right tentacle).

Figure 8. Operculum morphology (inner surface): A, Margarya oxytropoides; B, Margarya melanioides; C, Margarya monodi; D, Margarya francheti; E, Tchangmargarya yangtsunghaiensis; F, Tchangmargarya multilabiata sp. nov.; G, Anularya mansuyi; H, Anularya bicostata; I, Cipangopaludina chinensis. J, characters measured for morphological analysis of operculum: HO, height of operculum; HOS, height of opercular scar; WO, width of operculum; WOS, width of opercular scar.

Figure 9. Comparison of the operculum of Cipangopaludina, Margarya, Tchangmargarya, and Anularya with respect to parameters WO–HO (width of operculum × height of of operculum) and rOS (relative operculum scar, width of opercular scar × height of opercular scar/WO–HO).

Figure 12. Mature juvenile shell of Margarya species: A, Margarya melanioides, JH 13, Lake Jianhu; B, Margarya francheti, EHCC 12, Lake Erhai; C, Margarya monodi, IZCAS FG89681, Lake Dianchi; D, Margarya oxytropoides, DCXHJ 44, Lake Dianchi.