Tchangmargarya, HE, 2013

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 : 782-783

TCHANGMARGARYA HE, 2013

Type species: Margarya yangtsunghaiensis Tchang & Tsi, 1949 , by original designation.

Taxonomic remarks

Tchang & Tsi (1949) descibed M. yangtsunghaiensis from Lake Yangzonghai, and they pointed out that it greatly differs from any other Margarya species by having acute apex and extremely prominent regular nodules; however, they still treated it as a speices of Margarya because of its large solid shell with ramp-like shoulder, elevat- ed keels, and distribution limited to Yunnan. All the reasearchers followed their conclusions until Du et al. (2013) pointed out this species formed a monophyletic group and didn′ t cluster with any other Margarya species , doubting its delimitation of genus. Based on the morphological differences described by Tchang & Tsi (1949), He (2013) founded a new subgenus of Margarya , Tchangmargarya , for M. yangtsunghaiensis as the type species. Herein we elevated the subgenus Tchangmargarya to a full genus for phylogeny, and for extensive differences of shell, operculum, and anatomy, compared with Margarya .

Description

Shell large, up to nearly 70 mm in height; very thick and solid; mostly with seven whorls, including two protoconch whorls, well-developed subsutural ramp or depression at upper portion of each whorl, except for the protoconch; whorls generally with between three and five prominent spiral keels, and enormous obvious axial ribs on each whorls, crossing into regular and elevated nodules, nodules small and dense on upper whorls, gradually becoming large and sparse on lower whorls, lower keel always covered by upper suture, and thus nearly invisible on the spiral whorls; two incomplete spiral ribs with elevated nodules extending onto umbilical area; aperture ovate; umbilicus small or absent.

Operculum corneous, ovate, reddish to yellowish brown, with subcentral nucleus and concentric growth lines; nucleus with few grains or veins; opercular scar large, relatively rough, outside smooth, obviously thickened, but the margin of operculum thin; operculum slightly smaller than aperture.

Radula with about 100–140 rows of teeth, each with one central tooth, one lateral tooth, and two marginal teeth on either side of it; outer marginal teeth with between ten and 16 denticles.

Body and mantle colour of living animals transparent white with dense yellow or orange pigment spots above ( Fig. 7E ); foot comparatively small, with large opercular lobe, two cephalic tentacles of equal length, about 4.5–6.0 mm long, right tentacle thickened in males, modified into a penis ( Fig. 7H ). Gonochoristic, prostate in male reddish yellow, about 20 mm long, testis auratus about 25 mm long. Gravid females retaining one or two developing juveniles in uterus, with size at birth mostly exceeding 10 mm.

Comparative remarks

Tchangmargarya differs from Margarya and Anularya gen. nov. by two incomplete spiral ribs with elevated nodules in the umbilical area, an operculum smaller than the aperture, with an almost smooth nucleus, and with few grains or veins only, thickened outside of the opercular scar but with a thin margin. Extant Tulotoma Haldeman, 1840 endemic to Alabama, USA, has nodules similar to Tchangmargarya ; however, its shell is smaller, having no plate area on each whorl or two keels with nodules on the base of the body whorl, and an operculum that is hemicycle in shape. As for anatomical characters, Tchangmargarya resembles Margarya in having a small foot but large opercular lobe and similar colour pattern of body. It differs by its reddish yellow prostate and much shorter cephalic tentacles in males ( Fig. 7H ).

TCHANGMARGARYA YANGTSUNGHAIENSIS

Figures

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).