Trypanocochlea lopburiensis, 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 : 40

Trypanocochlea lopburiensis sp. nov.

( Fig. 25 I–N)

Etymology. After the Lopburi Province in which the studied gastropod material was found.

Holotype. ESKU-19-LP 210

Paratypes. ESKU-19- LP 201, 203, 204, 206, 211, 218, 221.

Dimensions (mm): ESKU-19- LP 201: height = c. 1.1; width = 0.6. ESKU-19- LP 203: height = c. 1.1; width = 0.5. ESKU-19- LP 204: height = c. 1.0; width = 0.5. ESKU-19- LP 206: height = c. 1.9; width = 0.8. ESKU-19- LP 210: height = 1.5; width = 0.6. ESKU-19- LP 211: height = c. 1.1; width = 0.6. ESKU-19- LP 218: height = 1.3; width = 0.5. ESKU-19- LP 221: height = c. 0.7; width = c. 0.4.

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 very small, high-spired, turritelliform, slightly cyrtoconoid comprising about six whorls; earliest two whorls (probably protoconch) convex, without visible ornament, somewhat mammilated; suture distinct; whorls low with evenly increasing whorl expansion after early first whorl, angulated at about mid-whorl with concave subsutural ramp; lower whorl below angulation concave; strong spiral cord located at mid-whorl at angulation forming periphery, with numerous small nodules (crenulated); additional weak spiral threads situated at subsutural position and second spiral thread located emerging from lower suture; whorl face on ramp and lower whorl smooth without visible ornament; base flatly convex without ornament; shallowly minutely phaneromphalous or anomphalous; aperture not well-preserved, seemingly circular with short slit.

Remarks. These tiny shells are assigned to the genus Trypanocochlea due to their high spire and the nodular spiral keel which is situated at the mid-whorl. However, due to preservation it is unclear whether a selenizone is present on the keel in the present specimens. Trypanocochlea parva Nützel, 2012 from the Akasaka Limestone, Japan is the only other Permian nominate species; it has much larger nodes on the keel, the keel is more pronounced, it is not cyrtoconoid but conical. Both species share a mammilate protoconch probably representing a larval shell of the caenogastropod type. The genus Donaldospira holds similar species but this genus lack nodes on the median keel. Donaldospira taosensis Kues & Batten (2001 , fig. 9.30) from the Middle Pennsylvanian of New Mexico is similar but has higher whorls and several spiral threads above and below the carina (that lacks crenulation), which are not present in the present specimens. D. carinata Bandel, 2002 b from the East Mount Shale, Pennsylvanian of Texas, USA has a much more protruding peripheral carina. The present specimens are much smaller than the other Permian Donaldospira species and the spiral cord at mid-whorl is weaker in the other species and the carina is not crenulated. Trypanocochlea lopburiensis is established as a new species that yields approximately 10 specimens in the present collection.

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).

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.