The St. Cassian Formation, Italy, has yielded the most diverse marine invertebrate fauna known from the Triassic. A quarter of all described Triassic gastropod species has been reported from this formation. Most of the gastropod species from the St. Cassian Formation were erected in the 19th century and many of them are known only from their original figures and descriptions. The failure to study type specimens resulted in many erroneous identifications by subsequent authors. Here, we revise the slit band gastropods (Pleurotomariida) from the St. Cassian Formation—one of the major groups present in this formation. A total of 77 nominate Pleurotomariida species belonging to 29 genera and 11 families are present in the St. Cassian Formation which comprises approximately 14 % of the total nominate gastropod species of that formation. In addition, we revise several taxa that had been wrongly assigned to Pleurotomariida. As other gastropod clades, Pleurotomariida experienced a major extinction at the end-Permian mass extinction event. As in the Late Palaeozoic, their relative abundance in gastropod faunas continued to be 30 % in some Anisian faunas but decreased to 5–10 % afterwards. Their diversification at generic level became interrupted by an extinction event within the Carnian, probably by the Carnian Pluvial Event. As a result of their sluggish recovery compared to the other gastropod groups, their species diversity decreased from 26 % during the Permian to 18 % during the Triassic. Type specimens of the following genera are studied: Proteomphalus, Rhaphistomella, Temnotropis, Kittlidiscus, Stuorella, Schizogonium, Wortheniella, Bandelium, Lancedellia, Rinaldoella, Pseudowortheniella, Paleunema, Ampezzalina, Bandelastraea, Cheilotomona, Pseudoscalites, Delphinulopsis, and Cochlearia. Nine new pleurotomariidan genera are erected: Amplitomaria, Pseudoananias, Lineacingulum, Pressulasphaera, Cancellotomaria, Acutitomaria, Lineaetomaria, Nodocingulum, and Striacingulum. Eight new species are described: Schizogonium undae, Acutitomaria kustatscherae, Wortheniella klipsteini, Wortheniella paolofedelei, Rinaldoella tornata, Nodocingulum ernstkittli, Nodocingulum? turris, and Laubella subsulcata. Eoworthenia frydai is a new replacement name for Worthenia rarissima Barrande.

Pleurotomariida have the longest fossil record among living gastropods and are diverse and abundant in the middle and upper Palaeozoic. Its traditional classification is based on adult shell characters. The early shell morphology has been largely unknown. We describe exceptionally well‐preserved Pleurotomariida from the Pennsylvanian marine shales of Texas, Oklahoma, Kansas and Ohio. In total, 38 species representing 19 genera are described, including 10 new species, one new genus and one new subgenus:Eirlysella buckhornensisgen. et sp. nov.,Shansiella(Oklahomaella)globilineatasubgen. et sp. nov.,Phymatopleura girtyi,Phymatopleura conica,Worthenia(Yochelsonospira)kuesi,Dictyotomaria turrisbabel,Paragoniozona yanceyi,Spiroscala shwedagoniformis,Peruvispira oklahomaensis,Baylea tenera. Replacement names areParagoniozona ornatanom. nov. (forPleurotomaria asperaGirty),Spiroscala quasipulchranom. nov. (forEuconospira pulchraBatten). The early ontogenetic shells including protoconchs and early teleoconchs are reported in detail for the first time for most taxa. Most species have a protoconch of one whorl as that of living Vetigastropoda. Planktotrophic protoconchs (multi‐whorled larval shells with sinusigera) are reported forPlatyzonaandPeruvispira; they are therefore placed in the family Goniasmatidae (Caenogastropoda). Repaired shell scars were found in juvenile Pleurotomariida specimens (c. 1 mm), suggesting exposure to predation from an early stage of ontogeny. Pleurotomariida are strongly dominant in surface samples of the Finis Shale (Texas) but in bulk samples using fine mesh‐sizes, dominance is much less pronounced, indicating a change in clade proportion depending on sampling method. The taxonomic richness and abundance of Pleurotomariida seen in these Carboniferous shales have not been reported from post‐Triassic formations.

Permian gastropods from Thailand have been extensively studied over the last few years. The earliest known fossil collection was recovered in 1967 but has never been figured or described. Here, we document this historically important gastropod assemblage excavated from the upper-Lower to Middle Permian Ratburi Group of Khao Mang Lat in the Ban Kao District of Kanchanaburi Province, Central Thailand. The material comprises approximately 200 specimens, almost all of which represent a new species, Peruvispira kanchanaburiensis sp. nov. (Goniasmatidae), together with a single individual of Orthonychia sp. (Orthonychiidae = Platyceratidae). This exceptionally low-diversity community is unusual in comparison to Permian gastropod faunas reported from elsewhere, and could reflect either a low temperature palaeoenvironmental setting or priority effects resulting from early establishment of planktotrophic larvae within the local habitat. Baran Karapunar [karapunar@snsb.de], SNSB-Bayerische Staatssammlung für Paläontologie und Geologie, Richard-Wagner-Str. 10, 80333 München, Germany, and Department of Earth and Environmental Sciences, Paleontology & Geobiology, Ludwig-Maximilians-Universität München, Richard-Wagner-Str. 10, 80333 München, Germany; Alexander Nützel [nuetzel@snsb.de], SNSB-Bayerische Staatssammlung für Paläontologie und Geologie, Richard-Wagner-Str. 10, 80333 München, Germany, and Department of Earth and Environmental Sciences, Paleontology & Geobiology, Ludwig-Maximilians-Universität München, Richard-Wagner-Str. 10, 80333 München, Germany, and GeoBio-Center, Ludwig-Maximilians-Universität München, Richard-Wagner-Str. 10, 80333 München, Germany; Chatchalerm Ketwetsuriya [ketwetsuriya.c@gmail.com], Department of Earth Sciences, Faculty of Science, Kasetsart University, 10900 Bangkok, Thailand.

A new Permian gastropod assemblage from the Roadian (Middle Permian) Khao Khad Formation, Saraburi Group (Lopburi Province, Central Thailand) which is part of the Indochina Terrane, has yielded one of the most diverse Permian gastropod faunas known from Thailand. A total of 44 gastropod species belonging to 30 genera are described herein, including thirteen new species and one new genus. The new genus is Altotomaria. The new species are Bellerophon erawanensis, Biarmeaspira mazaevi, Apachella thailandensis, Gosseletina microstriata, Worthenia humiligrada, Altotomaria reticulata, Yunnania inflata, Trachydomia suwanneeae, Trachyspira eleganta, Heterosubulites longusapertura, Platyzona gradata, Trypanocochlea lopburiensis and Streptacis? khaokhadensis. Most of the species in the studied assemblage represent vetigastropods (35.6%) and caenogastropods (26.7%) and most of the species belong to Late Palaeozoic cosmopolitan genera. The studied faunas come from shallow water carbonates that are rich in fusulinids, followed by gastropods, ostracods, bivalves and brachiopods. The gastropod assemblage from the Khao Khad Formation shares no species with the gastropod assemblages from other Permian formations in Thailand, the Tak Fa Limestone and the Ratburi Limestone. However, it is similar to the Late Permian gastropod faunas from South China of the Palaeo-Tethys, therefore it suggests that the Indochina Terrane was not located far from South China.

Mid‐ to higher‐latitude shallow marine environments are suggested to serve as refugia for organisms during intervals of rapid environmental change associated with hyperthermals. To understand the role of these environments during hyperthermals, we herein investigate the Permian–Triassic environmental crisis, which led to the most severe mass extinction event in the Phanerozoic. Our analysis of siliciclastic deposits from the Boreal Ocean from Lusitaniadalen, Svalbard, reveals a distinct increase of the lipid biomarkers C ₃₃ ‐ n ‐alkylcyclohexane (C ₃₃ ‐ n ‐ACH) and phytanyl toluene following the extinction event. This increase does not appear to reflect facies changes. Rather, it coincides with the extinction horizon, and persists into the lowermost Triassic (Griesbachian). Our findings suggest that neither C ₃₃ ‐ n ‐ACH nor phytanyl toluene are linked to short periods of photic zone euxinia recorded at Lusitaniadalen, but rather are derived from a specific group of phytoplankton. This indicates that higher‐latitude ecosystems may have supported regional blooms of unknown primary producers after the Permian–Triassic mass extinction, thus explaining the selective survival of some marine organisms. We also identify (albeit in lower abundance) C ₃₃ ‐ n ‐ACH and its pseudohomologs in northern Italy, which is the first report of n ‐ACHs in the tropical Tethys region across the Permian–Triassic transition outside of South China, highlighting the wide paleogeographic distribution of this biomarker. Phytanyl toluene, however, is found exclusively in deposits recording higher‐latitude ecosystems, and is likely linked to organisms occupying a similar ecological niche as the source organism of C ₃₃ ‐ n ‐ACH in these settings.