Knightella irregularis ( Longstaff, 1933 )

Ketwetsuriya, Chatchalerm, Karapunar, Baran, Charoentitirat, Thasinee & Nützel, Al- Exander, 2020, Middle Permian (Roadian) gastropods from the Khao Khad Formation, Central Thailand: Implications for palaeogeography of the Indochina Terrane, Zootaxa 4766 (1), pp. 1-47 : 38

Knightella irregularis ( Longstaff, 1933)

( Fig. 25 B–E)

Knightia irregularis Longstaff, 1933: 118 , pl. 12, figs 4–5; Knight, 1941: 164, pl. 49, fig. 6a–b.

Material. Two specimens: ESKU-19- LP 41, 84.

Dimensions (mm): ESKU-19- LP 41: height = c. 16.6; width = 6.1. ESKU-19- LP 84: height = 8.9; width = 4.0; apical angle = 42 º.

Description. Shell high-spired, slender; largest specimen consisting of 10 whorls; protoconch smooth, seemingly about two orthostrophic whorls; whorls low, gently increasing; whorls smooth; whorl face evenly convex or somewhat pendent with periphery at mid-whorl or somewhat below; sutures moderately deep, distinct; base evenly convex, rounded; anomphalous; aperture unknown.

Remarks. The present specimens closely resemble the type species, Knightella irregularis ( Longstaff, 1933) from the Carboniferous, Scotland as re-described and illustrated by Knight (1941, p.165, pl. 49, fig. 6a–b), although the present specimens are much larger. The general features of this species (i.e., high spire, sharply rounded and somewhat pendent whorl profile, a body whorl which is two-fifths of the total height, rounded base, anomphalous shell and slightly protruding protoconch) are obviously identical with the present specimens. Other similar species are K. hydrobiformis Nützel, 2012 and Knightella sp. from the Middle Permian Akasaka Limestone of Japan (Nützel & Nakazawa, 2012) and also several Knightella species which have been reported by Nützel (1998) from the Pennsylvanian of the USA. However, these species are smaller and have less convex whorls. Loxonema karabolkensis Licharev, 1975 (p. 78, pl. 13, figs 5–8) from the Pennsylvanian of Russia is similar but it differs in having a dense spiral ornament on the whorls. The present specimens are also similar to Protostylus ; however, this genus has flatter whorls. This is the first known member of the genus Knightella in Thailand which extends the range of this species and genus to the Middle Permian and expands its distribution to the eastern Palaeo-Tethys.

Figures

FIGURE 25. A, Donaldospira sp., ESKU-19-LP 85. B–E, Knightella irregularis (Longstaff, 1933), B–C, ESKU-19-LP 41. D–E, ESKU-19-LP 84. F–H, Protostylus sp., F, ESKU-19-LP 39. G–H, ESKU-19-LP 64. I–N, Trypanocochlea lopburiensis sp. nov. I, M, ESKU-19-LP 210, holotype; oblique view of early whorls to show protoconch. J, ESKU-19-LP 201, paratype. K, ESKU-19-LP 203, paratype. L, ESKU-19-LP 206, paratype; lateral view of early whorls to show protoconch. N, ESKU-19-LP 221, paratype. O–R, Streptacis? khaokhadensis sp. nov., O–P, ESKU-19-LP 214, holotype. Q–R, ESKU-19-LP 213, paratype. Scale bars represent: 2 mm (A–H); 200 μm (I–R).