Sheldonia wolkbergensis, Herbert, 2016

Herbert, David G., 2016, New narrow-range endemic land snails from the sky islands of northern South Africa (Gastropoda: Streptaxidae and Urocyclidae), European Journal of Taxonomy 236, pp. 1-29 : 21-26

Sheldonia wolkbergensis sp. nov.

urn:lsid:zoobank.org:act:C7607188-AF52-4258-BF6A-4956282B6671

Figs 8 , 13–16

Etymology

Named after the Wolkberg massif, to which the species is endemic.

Material examined

Holotype

SOUTH AFRICA: Limpopo, Wolkberg, Baccarat Forest , 23.88680° S, 30.01633° E, 1485 m, northern mist-belt forest, in leaf-litter, D. Herbert, L. Davis & M. Cole, stn 14-09, 26 Nov. 2014, diameter 7.7 mm, height 5.2 mm ( NMSA P0156 /T4074, body in ethanol).

Paratypes (listed north to south)

SOUTH AFRICA: Limpopo, Wolkberg, Grootbosch Forest, 23.76551° S, 30.00253° E, 1600 m, Afromontane forest, living in leaf-litter, J. Swaye, stn L109, Dec. 2001 ( NMSA W2263/T4108, three dry specimens); Wolkberg, Swartbos Forest, 23.88189° S, 29.99411° E, 1425 m, Afromontane forest, in leaflitter, J. Swaye, stn L133, Dec. 2001 ( NMSA W2084/T3166, two specimens, bodies in ethanol); same data as holotype ( NMSA P0351/T4075, four specimens, bodies of two in ethanol); Wolkberg, Baccarat Forest, 23.88680° S, 30.01633° E, 1485 m, Afromontane forest, in leaf-litter, J. Swaye, stn L103, Dec. 2001 ( NMSA W2260/T3167, one dry specimen); Wolkberg, New Agatha Forest, 23.98298° S, 30.07696° E, 1620 m, Afromontane forest, in leaf-litter, J. Swaye, stns L121, L125, Dec. 2001 ( NMSA W2258/T3168, two specimens, body of one in ethanol).

Type locality

SOUTH AFRICA: Limpopo, Wolkberg, Baccarat Forest, 23.88680° S, 30.01633° E, 1485 m.

Identification

A small species characterised by its glossy, uniformly yellowish-brown shell, smooth protoconch and rimate columella lip. Distal genitalia with an atrial diverticulum, a large gametolytic sac with a very short duct, and a curved epiphallic caecum situated much closer to insertion of vas deferens than to penis retractor.

Description

SHELL ( Fig. 13 ). Small, globose-lenticular to subglobose; largest specimen with diameter 9.4 mm, height 6.5 mm; H:D 0.65–0.75; periphery close to or just below mid-whorl, evenly rounded; suture shallowly but distinctly indented, inserting well above periphery; very thin and delicate. Protoconch diameter 1.40–1.53 mm; junction with teleoconch indistinct; smooth except for indistinct microscopic scratchlike spiral lines. Teleoconch of up to 2.5 whorls; whorls expanding moderately rapidly, with irregular and mostly weak growth-lines; spiral sculpture obsolete. Columella concave, its adapical region reflected over umbilical region and fused to adjacent part of base, forming a narrow flattened umbilical channel; aperture roundly lunate. Translucent, more or less uniformly yellowish-brown; apical and basal surfaces both glossy.

EXTERNAL FEATURES ( Fig. 14 ). Head and neck dark grey dorsally, pale yellowish-buff ventrally, grey pigmentation associated with skin granules and thus appearing as dense spotting; tentacles brownish grey; posterior of foot more uniformly darker grey, particularly caudal appendage, but also with minute white pigment granules scattered between skin grooves; pulmonary region strongly pigmented. Mantle edge with well-developed right and left body lobes bearing some grey pigmentation; right and left shell lobes elongate-trigonal when extended over shell, pale and translucent, with scattered minute cream pigment granules. Pulmonary lining behind mantle edge bordered with cream and black blotches in a variable pattern; additional dark blotches and bands posterior to this with a very prominent and welldefined black band overlying primary ureter, to right of pale tissues of kidney; a further well-defined line of cream pigment to right of (i.e., dorsal to) black band. Spire viscera brown with occasional cream blotches and sparse, irregularly branching cream venation, but little or no black pigmentation. The caudal pit and appendage well developed.

RADULA ( Fig. 15 ). Formula R+8+(1–2)+(40–50); rachidian tricuspid, laterals essentially bicuspid with a mesocone and strong basal ectocone, but also with a minute endocone on side of mesocone; laterals followed by 1–2 intermediary teeth and then a long series of marginals; marginals curved, bearing a large terminal cusp with a smaller subterminal cusp, followed by a series of finer serrations on concave outer margin, these proportionately stronger on smaller teeth toward edge of radula.

DISTAL GENITALIA ( Fig. 16 ). Penis of moderate length, tapering somewhat toward apex, enclosed in a thin sheath, upper portion with a single coil; retractor muscle attached above this at penis apex; interior of penis with a verge at about one-third to half length from base ( Fig. 16B ); verge comprising a smooth trigonal flap encircling a central pore; penis lumen below verge (preputial region) with numerous, close-set papillae; lumen above verge with slender longitudinal folds. Epiphallus with a short, recurved caecum arising one-quarter of its length from insertion of vas deferens; proximal portion of epiphallus between vas deferens and caecum swollen, its lumen contents opaque white; distal portion more slender and resembling penis. Flagellum divided into F1 and F2; F1 short, swollen and with 6–7 transverse internal diverticulae; F2 somewhat longer, with 1–2 tight coils, with a simple tube-like internal core. Vas deferens simple and slender, tracking course of penis and vagina in life. Genital atrium large, with a conspicuous diverticulum arising on its antero-medial side; in life diverticulum lies beneath buccal mass; interior of diverticulum with anastomosing ridges and a large fleshy fold (stimulator), itself with superficial ridges ( Fig. 16C ). Vagina short, somewhat swollen; gametolytic sac large and thin-walled, globose but narrowing apically; gametolytic duct very short; base of free oviduct swollen, off-white; spermoviduct divided into distinct prostatic and oviductal portions. In one specimen the male distal genitalia were partially everted ( Fig. 16D ) with both the penis and the atrial diverticulum occupying a position in the genital atrium. The diverticulum was completely evaginated, with the fleshy stimulator at its tip. Spermatophore unknown.

Distribution ( Fig. 8 )

A narrow-range endemic, known only from the Wolkberg region of the northern Drakensberg Escarpment in Limpopo, South Africa; at altitudes between 1425 and 1620 m above sea level.

Habitat

Northern mist-belt forest ( Mucina & Rutherford 2006); all material collected to date was found in leaflitter.

Remarks

Sheldonia wolkbergensis sp. nov. is superficially similar to S. monsmaripi sp. nov. from forests on the neighbouring escarpment to the south, and both are unusual in possessing an atrial diverticulum. However, as discussed above, the similarities may be convergent. In terms of shell morphology, the two are easily distinguished on the basis of the columella lip morphology. In S. monsmaripi sp. nov., the columella is not reflected to form a rimate umbilical channel and an umbilicus is completely absent. There are additional differences in the distal genitalia that are detailed in the remarks relating to S. monsmaripi sp. nov. The pigmentation of the viscera is similar in both species, but in S. monsmaripi sp. nov. the spire viscera are darker and there is more cream pigmentation. S. wolkbergensis sp. nov. is evidently a small species, with individuals of 6.5 mm shell diameter possessing well-developed distal genitalia.

The morphology of the distal genitalia of this species resembles that of species of Angustivestis Pilsbry, 1919 from central Africa ( Van Mol 1970), but the duct of the gametolytic sac is much shorter in S. wolkbergensis sp. nov. and the whorls of the shell do not expand so rapidly.

Figures

Fig. 8. Map showing the distribution of new urocyclid species in relation to centres of plant endemism (Van Wyk & Smith 2001). Green circles = Ptilototheca soutpansbergensis gen. et sp. nov.; blue triangles = Sheldonia wolkbergensis sp. nov.; maroon squares = Sheldonia monsmaripi sp. nov.; pale blue = Soutpansberg Centre; pale orange = Wolkberg Centre (Serala Subcentre); pale green = Wolkberg Centre (Blyde Subcentre). Contours at 1000 and 2000 m.

Fig. 13. Sheldonia wolkbergensis sp. nov., holotype, diameter 7.7 mm, height 5.2 mm (NMSA P0156/ T4074).

Fig. 14. Sheldonia wolkbergensis sp. nov., holotype, shell diameter 7.7 mm (NMSA P0156/T4074).

Fig. 15. Sheldonia wolkbergensis sp. nov., radula, holotype (NMSA P0156/T4074). A. Rachidian and lateral teeth. B. Rachidian and innermost lateral teeth. C. Inner marginal teeth. D. Outer marginal teeth. Scale bars: A–C = 50 µm; D = 25 µm.

Fig. 16. Sheldonia wolkbergensis sp. nov., genitalia. A. Entire reproductive tract. B. Basal portion of penis opened to show penial verge. C. Atrial diverticulum dissected to show atrial stimulator. D. Partially everted distal genitalia with penis and stimulator protruding into genital atrium. A–C. Holotype (NMSA P0156/T4074). D. Paratype (NMSA W2258/T3168).