Chilonopsis lanceoloideus, Gerlach & Griffiths & Hume & Louchart & Sorrel & Cairns-Wicks, 2025

Gerlach, Justin, Griffiths, Owen, Hume, Julian P., Louchart, Antoine, Sorrel, Philippe & Cairns-Wicks, Rebecca, 2025, Diversity of the extinct land snail genus Chilonopsis of St Helena (Mollusca: Gastropoda: Achatinidae), European Journal of Taxonomy 1007, pp. 176-210 : 196-197

Chilonopsis lanceoloideus sp. nov.

urn:lsid:zoobank.org:act:15C89CAB-ED18-4EFC-9B26-805DFB4FF0BB

Figs 4d , 7e–f , 9d–f

Diagnosis

A moderately elongate Chilonopsis with an evenly lanceoloid shape. Adults with fewer whorls than other Chilonopsis (4.5–5.25 mm compared to 5.0–9.0 mm). Teleoconch sculpture with distinctively wavy radial striae, not as prominent as the scalloped radials of C. helena . The only non-elongate Chilonopsis with a columellar ridge.

Etymology

Named due to its lanceoloid shape, which is unique in the St Helena terrestrial mollusc fauna.

Type material

Holotype SAINT HELENA • adult shell; Sandy Bay PG 1 valley toward Potato Gut, surface finds; 15°59′54.3″ S, 5°42′42.7″ W; Aug.–Sep. 2022; “AtlantAves” leg.; NHMUK 20240171 .

Paratypes SAINT HELENA • 1 subadult, 4 juvenile shells; same data as for holotype; NHMUK 20240172 .

Other material examined

SAINT HELENA • 6 shells (3 adults, 2 subadult, 1 broken); Castle Rock Plain (GB 882 SH); 1995; P. and M. Ashmole leg.; MSH (1 used in SEM – Fig. 7e ) .

Description

Relatively small (height 15.9–21.3 mm; Table 1 ). Ovately conical to lanceoloid. Thin. Apex obtuse. 4.5– 5.25 moderately convex whorls; no trace of shouldering. Body whorl ovate, widest below mid-point from apex to base of aperture. Sutures shallowly impressed, very slight bossing apparent ( Fig. 7e ). Protoconch of 1.25–1.75 whorls ornamented with 7–12 fine spiral striae ( Fig. 7e ). Teleoconch ornamented with 6 indistinct spiral striae, largely obscured by fine wavy radial striae and coarse radial growth lines. The overlapping of the radial and spiral striae creates a fine scalloped pattern ( Fig. 7e ). Aperture ovate, rounded at base (angled in subadult). Lip very narrowly and evenly expanded, not thickened, reflected onto umbilicus. Margins joined by a thin, shiny parietal callus. Columella oblique, thickened at insertion and forming a low ridge with a concavity on its surface ( Fig. 9f ); slightly pressed over umbilicus. Umbilicus open, narrow.

All shells bleached but white zig-zag markings are visible on the spire, fading but still detectable onto the body whorl.

Distribution

Known only from the south of St Helena ( Fig. 11 ): Sandy Bay and Castle Rock Plain.

Remarks

Closely resembles C. blofeldi ; both species lacking apertural thickenings and being superficially similar in shape, but the present species is smaller and wider (maximum length 21.3 mm compared to 25.9 mm for the smallest C. blofeldi and height/diameter 1.51–1.76 compared to 1.68–2.04), and is more evenly lanceoloid in shape. The presence of a slightly expanded lip and parietal callus demonstrates that C. lanceoloideus sp. nov. are not merely immature C. blofeldi . The present taxon differs from C. blofeldi in size; having a rounded apex; having less convex whorls, the widest part of the shell below the mid-point from apex to base of aperture; shallower sutures and a rounded base to the aperture; a slightly expanded lip; angled columella with a low vertical ridge and slight depression.

Figures

Fig. 4. Species of Chilonopsis. a. C. aurisvulpina (Holten, 1802) (NHMD-172594). b. C. helena (Quoy & Gaimard, 1832) (NHMUK 20240185). c. C. blofeldi (Forbes, 1852) (NHMUK). d. C. lanceoloideus sp. nov., holotype (NHMUK 20240171). e. C. exulatus (Reeve, 1849) (UMZC I.105095). f. C. subtruncatus (E.A. Smith, 1892) (NHMUK 92.2.24.224-8). g. C. turtoni (E.A. Smith, 1892) (NHMUK 1892.2.24.209-218). h. C. subplicatus (G.B. Sowerby I, 1844) (MSH). i. C. melanioides (Wollaston, 1878) (ANSP 97326). Scale bar = 25 mm.

Fig. 7. Sculpture of species of Chilonopsis. a–b. Chilonopsis aurisvulpina (Holten, 1802) (Prosperous Bay Plain, P. & M. Ashmole, 1995), protoconch (a) and spire (b). c–d. Chilonopsis helena (Quoy & Gaimard, 1832) (Turks Cap summit, “AtlantAves”, Aug. 2022) scanning electron micrographs of protoconch (c) and body whorl (d). e. Chilonopsis lanceoloideus sp. nov. (Castle Rock Plain, P. & M.Ashmole, 1995) scanning electron micrograph of protoconch and spire. Scale bars = 500 μm.

Fig. 9. a–c. Chilonopsis blofeldi (Forbes, 1852). d–f. C. lanceoloideus sp. nov. a. Bulimus Blofeldi Forbes, 1852 figure (Forbes 1852). b. Specimen NHMUK un-numbered (ex Melliss). c. Aperture. d, f. Holotype (NHMUK 20240171). e. Paratype NHMUK 20240172. f. Aperture. Scale bar = 25 mm.

Fig. 11. Distributions of species of Chilonopsis Fischer von Waldheim, 1848.