Biarmeaspira mazaevi, Ketwetsuriya & Karapunar & Charoentitirat & Nützel, 2020

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 : 13-14

Biarmeaspira mazaevi sp. nov.

( Fig. 10 )

Etymology. After Alexey Mazaev for his work on the Late Palaeozoic gastropods and establishment of this genus. Holotype. One specimen: ESKU-19-LP 1 .

Dimensions (mm): ESKU-19-LP 1: height = 11.0; width = c. 9.5; apical angle = 100º.

Type locality and stratigraphical range. Erawan Hill, Chong Sarika sub-district, Phatthana Nikhom district, located about 13 km east of Lopburi Province, Central Thailand ( Fig. 1 ), Khao Khad Formation, Saraburi Group, Middle Permian, Roadian.

Description. Shell moderately high-spired, turbiniform, earliest whorls missing, 4 whorls preserved; early teleoconch whorls convex, ornamented by up to four spiral lirae; later spire whorls with sharp angulation at mid whorl face; upper whorl face above angulation develops a concave subsutural ramp; ramp ornamented with several spiral threads; selenizone narrow, angulated, situated at middle angulation, ornamented with obscure lunulae, bordered by two distinct spiral cords; lower whorl face flat to concave, subvertical inclined about 10 degrees from axis, ornamented with up to eight widely spaced fine spiral lirae; lower whorl face twice as wide as upper whorl face; suture shallow and indistinct; lower part of the lower whorl face ornamented by two strongest spiral cords, representing periphery, interspace between the two cords markedly concave, wide and ornamented with additional 2 fine spiral lirae, lowest cord represents the basal edge; profile near basal edge swollen; base convex, ornamented by numerous widely spaced fine spiral cords that are stronger and more widely spaced than those on ramp and lower whorl face; aperture unknown.

Remarks. This single specimen is placed in the genus Biarmeaspira due to the presence of an angular selenizone and a strong spiral ornament. The early teleoconch is absent and the growth lines and the aperture are poorly preserved so that this generic assignment is not entirely beyond doubt. Another genus having a prominent spiral ornament, a swollen basal edge and an angular selenizone is the Triassic genus Sisenna . Sisenna has a lower spire compared to Biarmeaspira and it possesses an angulation on the early whorl face which later turns into selenizone during ontogeny, a characteristic that is absent in Biarmeaspira .

Biarmeaspira mazaevi sp. nov. can be differentiated from other Biarmeaspira species by its ornamentation and by having a swollen basal edge. B.? loatienensis ( Mansuy, 1914) from the Carboniferous of Loatien, Yunnan is very similar in shape, but is ornamented with more prominent spiral ribs on the upper and lateral whorl face. B.? choueitangensis ( Mansuy, 1912, pl. 18, fig. 12) shows a similar whorl morphology and might be closely related.

Figures

FIGURE 10. Biarmeaspira mazaevi sp. nov. ESKU-19-LP 1, holotype. All scale bars represent 2 mm.

FIGURE 1. Geological map of the study location at Erawan Hill, Chong Sarika sub-district, Phatthana Nikhom district, located about 13 km east of Lopburi Province, Central Thailand.