Chilonopsis helena ( Quoy & Gaimard, 1832 )

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 : 191-194

Chilonopsis helena ( Quoy & Gaimard, 1832)

Figs 4b , 8a–e , 7c–d

Helix helena Quoy & Gaimard, 1832: 111 .

Bulimus fossilis G.E. Sowerby I, 1844: 156 .

Bulimus digitale Reeve, 1849 : pl. 47 fig. 308.

Bulimus sealeianus Forbes, 1852: 4 , pl. 5 fig. 3.

Bulimus helena – Pfeiffer 1848: 198; 1859: 77; 1868: 121. — Melliss 1875: 122. — Wollaston 1878: 542. — Smith 1892: 266.

Bulimus fossilis – Forbes 1852: 4. — Jeffreys 1872: 264. — Melliss 1875: 122. — Wollaston 1878: 545.

Bulimus (Naesiotus) helena – Pfeiffer 1856: 698.

Bulimus sealeianus – Melliss 1875: 122.

Bulimus Seleianus [sic] – Wollaston 1878: 546.

Bulimus Helenae [sic] – Ancey 1887: 39 (for n. gen. Nesobia ). Helenopachnodus helena – Germain 1931: 169.

Chilonopsis helena – Crowley & Pain 1977: 560.

? Nesobia helena – Schileyko 1998: 182.

Diagnosis

A distinctly shaped ovate Chilonopsis in having very high shouldered whorls and being the only ovate species with a distinctly produced apex; sculpture more prominently scalloped than in other species.

Type material

Syntypes of Helix helena

SAINT HELENA • 2 shells; St Helena; M. Seel [= Seale]; MNHN-IM-2000-4649 ( Fig. 8a ) .

Syntypes of Bulimus fossilis

SAINT HELENA • 2 shells; NHMUK PI G 25270 to NHMUK PI G25272 ( Fig. 8b ). Originally in the Museum of Practical Geology ( Sowerby 1844) .

Syntypes of Bulimus digitale

SAINT HELENA • 2 shells; “ H. Helena … = B. digitale Reeve f 208”; NHMUK 20240185 ( Fig. 8c ). Exact matches for Reeve’s (1849) figure and description of specimens of unknown origin in the Cuming collection .

Syntypes of Bulimus sealeianus

SAINT HELENA • 2 shells; Sugar Loaf; E. Alexander leg.; NHMUK 1857.10 .16.33 ( Fig. 8d ) • 2 shells; Sugar Loaf; E. Alexander leg.; NHMUK P G25276-7. The latter transferred from the Museum of Practical Geology .

Other material examined

Typical form

SAINT HELENA • 1 shell; FMNH 48075 • 2 shells; FMNH 48250 • 3 shells; S foot of Sugarloaf Pt , gully; 9 Jun. 1961; M. and A. Loveridge; FMNH 173187 • 24 shells; The Barn ; A. Loveridge leg.; MCZ 203249 • 1 shell; Summit of the Barn; Spence and Layard collection; MM • 1 shell; Sugar Loaf 1, 0–30 m; “AtlantAves”; Aug.–Sep. 2022; MSH • 1 shell; Trechmann collection; NHMUK 2176 • 1 shell; The Barn ; E. Alexander leg.; NMHUK 1857.10.16.25 • 4 shells; Melliss leg.; Fulton collection; NHMUK 1873.11.19.44 • 4 shells; Melliss leg.; NHMUK 1873.11.19.112 • 1 shell; Side Path ; W.H. Turton leg.; NHMUK 1892.2 .24.229 • 4 shells; The Barn ; W.H. Turton leg.; NHMUK 1892.2.24.235-8 • 3 shells; Turks Cap Summit surface finds; Aug.–Sep. 2022; “AtlantAves” leg.; NHMUK 20240173 (1 used in SEM – Fig. 7c–d ) • 5 shells; Sugar Loaf 1; Aug.–Sep. 2022; “AtlantAves” leg.; NHMUK 20240175 • 3 shells; Sugar Loaf 2 SE, 0–30 cm: Aug.–Sep. 2022; “AtlantAves” leg.; NHMUK 20240176 • 1 shell; McAndrew collection ex Fulton; NHMUK • 2 shells; valley east of Bank’s ; C. Lewis leg.; NHMUK • 1 shell; Tomlin collection; NMW • 1 shell; Géret 1919; P. Dupuis collection; RBINS: IG:8907-HIST.3 • 1 shell; RMNH. MOL.251844 • 1 shell; Sugarloaf Ridge ; UF 564271 • 11 shells; USNM 126265 • 1 shell; USNM 197823 • 1 shell; USNM 703395 • 1 shell; ZMA.MOLL.379088 .

“sealeianus form”

SAINT HELENA • 3 shells; Sugar Loaf Hill ; 600 ft; 12 Feb. 1949; Mrs A. Loveridge leg.; MCZ 203243 • 2 shells; Sugarloaf ; W.H. Turton leg.; NHMUK 1892.2.24.18.2-5 • 5 shells; Sugarloaf; W.H. Turton leg.; NHMUK 1892.2.24.134-9 • 3 shells; Sugar Loaf 1,0– 30 cm; Aug.–Sep. 2022; “AtlantAves” leg.; NHMUK 20240177 • 55 shells; same data as for preceding; NHMUK 20240178 • 20 shells; Sugar Loaf 2 SE, 0–30 cm; Aug.–Sep. 2022; “AtlantAves” leg.; NHMUK 20240179 • 5 shells; Sugar Loaf 2 SE; Aug.–Sep. 2022; “AtlantAves” leg.; NHMUK 20240180 • 5 shells; Sugar Loaf 3; Aug.–Sep. 2022; “AtlantAves” leg.; NHMUK 20240181 • 1 shell; Trechmann collection; NHMUK • 1 shell; J.J. McAndrew collection ex Fulton; NHMUK • 1 shell; NMW. 1955.158.27974 • 3 shells; USNM 126266 .

Description

Relatively small (height 15.1–22.3 mm; Table 1 ). Ovately conical, very rarely elongate. Thick, slightly shiny in fresh specimens. Apex rounded, projecting distinctly. 5–7 convex whorls, usually high-shouldered, body whorl rounded. Sutures very deeply impressed and whorls strongly shouldered near suture. Protoconch of 1.5–2 whorls ornamented with 8–10 fine spiral striae ( Fig. 7c ). Teleoconch with 8–10 strong spiral ridges and fine, raised radial ridges. Radials bent where they cross the spirals, giving a scalloped effect ( Fig. 7d ). Aperture ovate, distinctly angled at base. Lip narrowly expanded; margins united by a thick callus. Callus runs onto the scalloped sculpture, giving an irregularly serrated appearance. Columella straight. Umbilicus open, surrounded by a slight ridge.

Protoconch reddish, rest of shell yellowish or pinkish to light brown with irregular zig-zag patterns of white streaks in well preserved specimens. The freshest specimens have a dark brown periostracum (NHMUK 92.2.24.18.25, 73.11.10.44). Aperture white.

Distribution

Restricted to the north and east of the island ( Fig. 11 ); The Barn over 600 m above sea level to the summit ( Melliss 1875; Wollaston 1878; Smith 1892); Side Path ( Melliss 1875 as B. fossilis ); Sugarloaf

Ridge, Quarry and summit ( Wollaston 1878 as B. fossilis ; Smith 1892; Forbes 1898 as B. fossilis ; Lewis, 2008); Turks Cap (new); Dry Gut (DG07 – Cairns-Wicks & Lambdon 2013).

The sealeianus form has only been found on the Sugar Loaf area.

Extinct: “although the shells are now dead, they appear of more recent date than the former species [most Chilonopsis ]” ( Melliss 1875: 122). Only dead shells were found by Wollaston, but not all were buried: “occurs rather abundantly on the extreme summit of the Barn, and in that immediate neighbourhood, lying loosely on the surface soil, beneath the shrubs of Salsola, &c., – where it has much the appearance of having lived at a comparatively recent period. At all events many of the examples have their colour and outer cuticle completely preserved, – though it is equally true that the majority of them are decomposed, decorticated, and colourless.” ( Wollaston 1878: 544). Smith thought it probably extinct in 1892 although he thought some may have been surviving at the time ( Smith 1892). Two specimens collected by Turton in the 1880s (NHMUK 57.10.16.25) are in perfect condition with, intact periostracal layers and appear to have been fresh when collected.

Remarks

Bulimus fossilis was considered a ‘somewhat unimportant modification’ of C. helena by Wollaston (1878) and synonymised with this species by Smith (1892), along with B. sealeianus . Crowley & Pain (1977) also included as synonyms B. digitatus Reeve, 1849 and B. relegatus W.H. Benson, 1851 , which are regarded here as synonyms of C. aurisvulpina . Bulimus sealeianus is a recognisable form, partially separated in the principal component analysis ( Fig. 3 ) but intergrades with typical C. helena , it differs in being straight-sided, not shouldered; narrower; an aperture forming 55–60% of shell height, rather than less than 55%; and a more evenly rounded base to the aperture. Crowley & Pain (1977) suspected NMW.1955.158.27974 to be a distinct species but the range of specimens examined here shows it to fall withing the range of variation of the present species.

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. 8. Chilonopsis helena (Quoy & Gaimard, 1832). a. Helix helena Quoy & Gaimard 1832, syntype MNHN-IM-2000-4649. b. Bulimus fossilis G.E. Sowerby I, 1844 (NHMUK PI G 25270-2). c. Bulimus digitale Reeve, 1849, syntype (NHMUK 20240185). d–e. Bulimus sealeianus Forbes, 1852, syntype (NHMUK 1857.10.16.33). e. Elongate specimen (NMW.1955.158.27974). Scale bar = 25 mm. Photos: a = D. Brabant, MNHN; c–d = NHMUK; e = H. Wood, NMW.

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

Fig. 3. Distribution of specimens across the first two principal components (Table 3). The main forms (species and recognisable varieties) are shown, with ellipses grouping the specimens of species recognised here.