Microkerkus sibaya, Herbert, 2017

Herbert, David G., 2017, A new genus and eight new species of tail-wagger snails from eastern South Africa, with a key to genera within Sheldonia s. l. (Gastropoda: Urocyclidae), European Journal of Taxonomy 309, pp. 1-50 : 28-32

Microkerkus sibaya sp. nov.

urn:lsid:zoobank.org:act:F4AD8FEE-EF1A-498A-B16A-CD7B60073056

Figs 6 , 20–22

Diagnosis

Shell globose-lenticular, lustreless, pale corneous brown, with irregular axial bands of short oblique white lines; protoconch non-punctate, but with distinct microspiral sculpture; columella straight, umbilicus present. Epiphallus long with a small, globular caecum just distal to mid-point; flagellum not bifid, with a long, loosely coiled f2.

Etymology

Name derived from the type locality, Lake Sibaya, in Maputaland, northern KwaZulu-Natal.

Material examined

Holotype

SOUTH AFRICA: KwaZulu-Natal, Lake Sibaya area , E of lake, approx. 27.35° S, 32.68° E, dune forest, B.H. Lamoral leg., Jul. 1967 ( NMSA V6958/T4169 , dry shell with body in ethanol).

Paratypes

SOUTH AFRICA: same data as holotype ( NMSA P0658/T4170, three dry shells with bodies in ethanol).

Description

SHELL ( Fig. 20 ). Globose-lenticular, spire relatively low; periphery at or close to mid-whorl, evenly rounded; H:D 0.77–0.78 (N=3); suture rather distinctly indented, inserting above periphery; thin, translucent pale corneous brown, with short oblique white lines, often arranged in irregular axial bands; surface satin-like, peri-umbilical region somewhat more glossy. Protoconch diameter 1.8–1.9 mm (N=2); junction with teleoconch poorly defined; sculptured with very fine, close-set, microscopic spiral lirae. Teleoconch of up to 2.25 whorls; sculpture similar to that on protoconch, but finer, producing satin-like shell surface; no axial component evident in microsculpture; growth-lines few on spire whorls, but more frequent on body whorl. Columella relatively straight, upper portion reflected, creating a distinct umbilical channel. Aperture somewhat D-shaped, indented by penultimate whorl in parietal region. Diameter up to 10.9 mm; holotype, diameter 10.0 mm, height 7.7 mm.

LIVING ANIMAL. Only the original specimens in 75% ethanol are available. Most of the colour in these has been lost and the head-foot and pulmonary cavity are now largely milky-white; the spire viscera apical to the pulmonary cavity are mid-brown with frequent sub-circular cream blotches in the superficial tissue.

RADULA ( Fig. 21 ). Formula R+9+(2–3)+(30–40); rachidian tricuspid, mesocone slender; anterior margin of shaft base not indented in mid-line; laterals essentially bicuspid with a mesocone and strong basal ectocone, but also with a minute endocone on side of mesocone; laterals followed by 2–3 teeth of intermediate shape; marginals relatively few in number, curved with a large terminal cusp and a weak subterminal one on outer (concave) margin; shaft lacking serrations; marginals progressively decreasing in size toward edge of radula, but otherwise morphologically similar.

DISTAL GENITALIA ( Fig. 22 ). Penis elongate and cylindrical, looped upon itself in mid-region and surrounded by a thin sheath; retractor muscle attached to penis apex; penis thin-walled, basal half slightly broader; lumen lining not well preserved, but with evidence of longitudinal folds; no evidence of a penial verge. Epiphallus relatively long, with a small globose caecum just distal to mid-point. Flagellum well developed, basal portion (f1) broader and with distinct transverse internal structure; distal portion (f2) more slender, with 1–2 loose coils; proximal part of epiphallus, close to insertion of vas deferens, with opaque white contents; vas deferens simple and slender, running beside vagina and free oviduct to join spermoviduct. Genital atrium small, lacking stimulator. Vagina of moderate length; gametolytic sac elongate-ovate, thin-walled, its duct relatively short; free oviduct not conspicuously enlarged; spermoviduct divided into distinct prostatic and oviductal portions.

SPERMATOPHORE. Unknown.

Distribution ( Fig. 6 )

Known only from the type locality.

Habitat

Northern Coastal Forest ( Mucina & Rutherford 2006).

Remarks

The genital morphology of this species is typical of Microkerkus and I have little hesitation in referring it therein. The form of the flagellum with a long f2 resembles that of M. maseruensis and M. symmetricus , and is quite distinct from the bifid flagellum found in M. burnupi , M. leucospira and M. pondoensis . In terms of shell morphology, perhaps the most similar species is M. chrysoprasinus (Melvill & Ponsonby, 1892) , but in that species the shell is more globose and the f2 portion of the flagellum is much shorter.

The occurrence of a species of Microkerkus close to the coast of northern Maputaland is somewhat surprising. The majority of Microkerkus species occur at high altitude (800 m to over 3000 m). The only other species occurring below this are M. leucospira and M. pondoensis , which favour open grassland

and marsh habitats along the coast and coastal scarp of central and southern KwaZulu-Natal and northeastern E Cape.

The irregular axial bands of short oblique white lines on the shell of this species are an unusual feature. I have not observed similar markings on the shells of any other southern African urocyclids. Although these are present in the shells of all four specimens available and may perhaps be distinctive of M. sibaya sp. nov., there is a possibility that they are in fact a preservation artefact. The intact specimens were preserved in ethanol for more than 40 years prior to the bodies being removed from the shells and the latter were then stored dry. There has undoubtedly been some deterioration in the substance of the shell, including partial decalcification close to the growing margin. These unusual lines may be a further manifestation of preservation-related damage rather than a species-specific character.

Conservation

Little can be said regarding the conservation of Microkerkus sibaya sp. nov. It is clearly a data deficient species for which targeted field work is needed. The type locality falls within the iSimangaliso Wetland Park World Heritage Site and is thus afforded a high level of protection.

Figures

Fig. 6. Distribution of Kerkophorus piperatus sp. nov. (triangles), Kerkophorus vittarubra sp. nov. (squares), and Microkerkus sibaya sp. nov. (cross). The population at Nkandla marked ‘?’ is a potentially hybrid population with shell characters resembling K. piperatus sp. nov., but with genitalia resembling K. vittarubra sp. nov. Contours at 1000 and 1500 m.

Fig. 20. Microkerkus sibaya sp. nov., holotype, diameter 10.0 mm (NMSA V6958/T4169), four views of shell and detail of pattern of white lines on body whorl, scale bar = 2.0 mm.

Fig. 21. Microkerkus sibaya sp. nov., radula (holotype, NMSA V6958/T4169). A. Rachidian and left lateral teeth. B. Rachidian and innermost lateral teeth. C. Inner left marginal teeth. D. Outer left marginal teeth. Scale bars = 50 μm.

Fig. 22. Microkerkus sibaya sp. nov., distal genitalia (paratype, NMSA P0658/T4170).