Chersaecia Gude, 1899

Páll-Gergely, Barna, 2018, Systematic revision of the Plectopylinae (Gastropoda, Pulmonata, Plectopylidae), European Journal of Taxonomy 455, pp. 1-114 : 10-12

Genus Chersaecia Gude, 1899

Chersaecia Gude, 1899d: 148 .

Endoplon Gude, 1899 d: 148. Syn. nov.

Chersaecia – Páll-Gergely et al. 2015 c: 9 .

Type species

Helix (Plectopylis) leiophis Benson, 1860 by original designation.

Included species and subspecies

Chersaecia auffenbergi sp. nov., C. brachyplecta ( Benson, 1863) comb. nov., C. dextrorsa ( Benson, 1860) , C. feddeni ( Blanford, 1865) comb. nov., C. goniobathmos ( Ehrmann, 1922) comb. nov., C. leiophis ( Benson, 1860) , C. leucochila (Gude, 1897) comb. nov., C. magna (Gude, 1897) comb. nov., C. mogokensis sp. nov., C. nagaensis nagaensis (Godwin-Austen, 1875) , C. nagaensis muspratti (Gude, 1897) , C. perarcta perarcta ( Blanford, 1865) , C. perarcta simplex ( Solem, 1966) , C. perrierae (Gude, 1898) , C. refuga ( Gould, 1846) , C. reversalis sp. nov., C. shanensis ( Stoliczka, 1873) , C. shiroiensis shiroiensis (Godwin-Austen, 1875) , C. shiroiensis subnagaensis subsp. nov., C. smithiana (Gude, 1897) comb. nov., C. woodthorpei (Gude, 1899) comb. nov.

Diagnosis

Shell sinistral or dextral, flat, widely umbilicated; in most cases protoconch seemingly ‘smooth’, but never glossy, matt or with tubercles of various size; aperture always with fold; parietal wall with one or two vertical lamellae and usually one or two long horizontal plicae reaching the parietal callus (main and lower plica); all palatal plicae horizontal, sometimes divided in the middle, in some species with several additional denticles posteriorly, in some species three horizontal plicae above and one below the vertical plate formed by the accretion of two plicae (similar to that of Plectopylis ).

Penis long, cylindrical to very short (reduced), internally with irregular longitudinal folds; penial caecum usually absent (rudimentary caecum rarely discernible); epiphallus present or absent; retractor muscle inserts on penis-epiphallus transition (or at the proximal end of penis); vas deferens slender, with thickened proximal part (or entire vas deferens thickened); vagina slender, usually long, with weak fibre muscles; bursa copulatrix long, with slightly or moderately thickened bursa; diverticulum conical to elongated, cylindrical, shorter than bursa (note that in C. perarcta simplex no diverticulum was reported).

Differential diagnosis

Chersaecia differs from Endothyrella , Gudeodiscus , Halongella , Sicradiscus and Sinicola by the usually tuberculated (not regularly ribbed) protoconch and the presence of long palatal plica extending to the parietal callus (the only exception is Gudeodiscus longiplica ). For the delimitation of Chersaecia from Plectopylis , see Remarks.

Distribution

The genus Chersaecia is known from northeastern India, Myanmar and northern Thailand ( Fig. 4 ).

Remarks

Gude (1899 d) diagnosed Chersaecia : “Sinistral or dextral. Umbilicus wide. Palatal folds horizontal or oblique. Sometimes with one or oblique or vertical plate”, whereas the diagnosis of Plectopylis s.s. was given as follows: “Sinistral. Shell flattened. Palatal armature: one vertical plate with three horizontal folds above, one below”. However, the fusion of the fourth and fifth palatal plicae into a vertical plate, which is very characteristic in Plectopylis , is also present in two species ( perrierae , shiroiensis ) assigned to Chersaecia by Gude (1899 d). Therefore this character-state cannot be used as a distinguishing character between the two genera. The peculiarity of Gude’s division is that all species of Plectopylis have two lamellae (sometimes connecting at their upper end), whereas all Chersaecia have only one lamella. These character-states, however, were mentioned by Benson (1860), but not Gude (1899 d). Gude (1914 b) referred to Plectopylis woodthorpei as the transitional form between Plectopylis and Chersaecia , probably because of the small size of the species, which is similar to Chersaecia , but with two lamellae, which is characteristic of Plectopylis sensu Gude (1899d) . Some specimens of Chersaecia perrierae show an intermediate character-state between the one and two lamellae types (see under that species). Moreover, the main difference between typical Chersaecia leiophis and Plectopylis goniobathmos is the absence ( leiophis ) and presence ( goniobathmos ) of an anterior lamella. These data suggest that the distinguishing mark between Plectopylis and Chersaecia cannot be the number of lamellae, because it shows clinal variability between species, or even between different specimens of the same sample ( Fig. 5 ). I therefore retain all species that are characterized by two lamellae fused at their upper ends, forming a structure which resembles the Greek letter lambda, in the genus Plectopylis . All other former species of Plectopylis , which possess two independent lamellae, are henceforth assigned to the genus Chersaecia .

The two species classified in the genus Endoplon Gude, 1899 (type species: Helix (Plectopylis) brachyplecta Benson, 1863 , by original designation) do not differ from some species of Chersaecia (e.g., C. magna ) in any notable shell characters, only by the coiling direction, which is insufficient to maintain the generic distinction. Therefore, Endoplon is moved to the synonymy of Chersaecia .

Gude (1899 d) classified all Vietnamese species in Endoplon. The revision of the Chinese species, however, revealed that the western (Burmese) and eastern (Chinese and Vietnamese) species are only distantly related (see Páll-Gergely & Hunyadi 2013). The genus Gudeodiscus was erected for the Vietnamese and Chinese taxa formerly placed in Endoplon.

Chersaecia is very diverse in terms of anatomical characters, especially the length of the penis and the presence or absence of the epiphallus. So far, the limited information on the genitalia is not in agreement with conchological characters. For example, the epiphallus is absent in C. perrierae , but present in the conchologically similar C. shanensis . In contrast, the conchologically different C. scabra sp. nov. is very similar to C. dextrorsa in the genital anatomy (especially the absence of the epiphallus and the vestigial penis). The species classified in this genus should be placed in at least two different genera based on the presence/absence of the epiphallus. However, I here refrain from describing any new genera, because the anatomy of the type species ( C. leiophis ), and the majority of the other species are unknown.

Table 1 summarizes the key characters of species of Chersaecia . Table 1 (continued on next page). Key characters, most similar species and distribution of species of Chersaecia Gude, 1899 , Hunyadiscus Páll-Gergely, 2016 and Naggsia Páll-Gergely & Muratov, 2016 .

Figures

Fig. 4. Distribution of the genera Chersaecia Gude, 1899 (ruled area), Hunyadiscus Páll-Gergely, 2016 (white area), Naggsia Páll-Gergely & Muratov, 2016 (black circles) and Plectopylis Benson, 1860 (grey shaded area).

Fig. 5. Photos (A, C, E) and schematic drawings (B, D, F) of parietal plicae and lamellae of Plectopylinae Möllendorff, 1898. A–B. Chersaecia shanensis (Stoliczka, 1873), loc. 20091018C (PGB, ex coll. Ohara). C–D. Chersaecia perrierae (Gude, 1898), loc. 20091019A (PGB). E–F. Chersaecia magna (Gude, 1897) comb. nov., holotype (NHMUK 1922.8.29.37). Posterior lamella indicated with red colour, anterior lamella and homologous structures indicated with blue. Not to scale. Photos: B. Páll-Gergely (A, C) and H. Taylor (E).