Altotomaria reticulata, 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 : 20-21

Altotomaria reticulata sp. nov.

( Fig. 15 )

Etymology. From Latin reticulata, meaning net-like, referring the reticulated ornament.

Holotype. Only specimen: ESKU-19-LP 83 .

Dimensions (mm): Height = c. 5.8; width = 4.4.

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 relatively high-spired, consisting of about 5 preserved whorls, whorls convex with periphery low on the whorl face; periphery in late teleoconch whorl with strong spiral cord angulating whorl face, first whorl(s) missing; first preserved whorl seemingly smooth (corroded), rounded; second whorl ornamented with spiral threads; whorl face above selenizone convex, narrow, ornamented with nearly orthocline regular axial threads and 2 spiral ribs, lower one bordering selenizone; selenizone situated above mid-whorl, flush with whorl face, ornamented regular with distinct lunulae and a median thread; selenizone bordered by two spiral cords; slit depth about 1/6 of last whorl; lower whorl face twice as wide as the upper whorl face; lower whorl face convex, ornamented with regularly spaced axial threads and 3 prominent, broad spiral cords, uppermost cord bordering selenizone; middle spiral cord strongest, representing periphery, interspace between spiral cords concave; suture slightly impressed, situated just below the lowermost spiral band; base convex, anomphalous, ornamented with axial threads and evenly spaced spiral cords of about same strength as those on upper whorl face; aperture unknown.

Remarks. The general whorl profile of Altotomaria reticulata sp. nov. is similar to that of species and genera of the subfamily Neilsoniinae but in Altotomaria , the lower edge of the selenizone does not represent the periphery and the selenizone is not raised above rest of the shell surface and as prominent as in neilsoniins. Median thread on selenizone has never been reported in Neilsoniinae . The reticulate ornament with stronger spiral cords, the relatively wide selenizone that is flush with the whorl face and bordered by two cords, the widely spaced regular lunulae that are in the same strength with the spiral ornaments, the presence of median thread on the selenizone suggest its affinity to the Triassic genera Euryalox Cossmann, 1897 and Eymerella Cossmann, 1897, therefore we tentatively place the new genus Altotomaria to Phymatopleuridae . The difference of the new genus from the latter two genera is the higher position of the selenizone. The position of the selenizone was regarded as informative for taxonomy and phylogeny (e.g., Knight et al. 1960). However, the position of the selenizone can differ among the species of the same genus (e.g., Kokenella , Stuorella ) and may also change during ontogeny (e.g. Pleurotomaria , Eirlysia ). A. reticulata sp. nov. resembles the neilsoniin species Apachella exaggerata Batten, 1989 (pl. 6, figs 3–10) from the Permian southwestern USA. Apart from the above discussed features that distinguish Altotomaria from the neilsoniin genera, A. exaggerata has less prominent spiral ornaments, sharper axial ornaments and differs in selenizone position.

Figures

FIGURE 15. Altotomaria reticulata sp. nov. A–E, ESKU-19-LP 83, holotype. All scale bars represent 1 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.