Cheilotomoninae, Nützel & Karapunar, 2023

Nützel, Alexander & Karapunar, Baran, 2023, On Triassic Murchisonia-like gastropods-surviving the end-Permian extinction to become extinct in the Late Triassic, Acta Palaeontologica Polonica 68 (3), pp. 539-559 : 544-545

Subfamily Cheilotomoninae nov.

Zoobank LCID: urn:lsid:zoobank.org:act:D1C49498-95D9-45A5-AF

D-12762FA25B99

Included genera: Cheilotomona Strand, 1928 , Trypanocochlea Tomlin, 1931 , Vistilia Koken, 1896 .

Type genus: Cheilotomona Strand, 1928 .

Diagnosis.—High-spired shells with slit band and a median whorl angulation; early teleoconch whorls have three spiral cords, which in later whorls become subsutural cord, whorl angulation and basal cord; nodes on whorl angulation before development of selenizone; selenizone develops late in ontogeny (4 th –7 th whorl); the lower border of selenizone or the selenizone itself situated at whorl angulation.

Remarks.—We place the subfamily Cheilotomoninae in Goniasmatidae due to their high-spired shell with a median selenizone. Species with a multi-whorled protoconch of the planktotrophic type with sinusigera or a paucispiral protoconch with sinusigera (characteristic of goniasmatids) have not been documented in the members of Cheilotomoninae . Cheilotomona has smooth early whorls with fluent transition to the teleoconch and a large initial indicating non-planktotrophic early ontogeny ( Karapunar and Nützel 2021, and see below).

Cheilotomona , Trypanocochlea , and Vistilia were previously placed in Murchisoniidae but Murchisonia lacks a prominent whorl crest on which the selenizone is situated, and this brings these genera close to Goniasma and thus they are placed in Gonismatidae. The protoconch of Trypanocochlea cerithioides is unknown and therefore, the possibility that Trypanocochlea belongs to Pleurotomariida and not to the caenogastropod family Goniasmatidae cannot be excluded. On the other hand, general whorl morphology, surface ornament (subsutural cord and strong axial ribs), and early ontogenetic shell development (nodular periphery, subsutural cord) supports its close association to Cheilotomona . Nützel and Nakazawa (2012) showed that a Permian Trypanocochlea s pecies from Japan has a mammilated protoconch of the caenogastropod type supporting a placement in Goniasmatidae .

Genus Cheilotomona Strand, 1928

Type species: Pleurotoma blumi Wissmann in Münster, 1841, Carnian (Upper Triassic), St. Cassian Formation, South Tyrol, Italy; subsequent designation by Diener (1926).

Remarks.—Replacement name for Cheilotoma Koken, 1889 , a junior homonym (see also Karapunar and Nützel 2021).

Stratigraphic and geographic range.—Anisian (Middle Triassic)–Carnian (Upper Triassic), Italy, Austria, Romania, Poland, Hungary, China.

Cheilotomona blumi (Wissmann in Münster, 1841) Fig. 4 .

1841 Pleurotoma blumi Wissmann n. sp., Wissmann in Münster: 123,

pl. 13: 47a–c

For exhaustive synonymy an chresonymy see Karapunar and Nützel (2021)

Remarks.—A detailed description of this abundant and variable species and other three Cheilotomona species from the St. Cassian Formation was given by Karapunar and Nützel (2021). Cheilotomona blumi has about two smooth initial whorls with an indistinct transition to the teleoconch and a diameter of the first whorl of about 0.3 mm indicating an early ontogeny without planktotrophic larval development. The selenizone develops very late. Mature whorls have an angulated periphery at which the selenizone is situated.

Bandel (2006: 92) stated that “if Cheilotomona blumi was found in Paleozoic deposits, it could be placed with the genus Goniasma ” and that “ Cheilotomona represents the last known member of the Orthonematidae ” (he considered Goniasmatidae and Orthonematidae to be synonymous, but see Nützel and Pan 2005 for a different opinion). Goniasma might be related to but is certainly not synonymous with Cheilotomona which has a strong axial ornament on early teleoconch whorls that is absent in Goniasma . Karapunar and Nützel (2021) placed Cheilotomona in the family Goniasmatidae Nützel and Bandel, 2000 (superfamily Orthonematoidea Nützel and Bandel, 2000 ).

Stratigraphic and geographic range.—Only known from the St. Cassian Formation, Carnian (Upper Triassic), N Italy.

Figures

Fig. 4. Goniasmatid caenogastropod Cheilotomona blumi (Wissmann in Münster, 1841), Carnian, St. Cassian Formation, Italy. A. MB.Ga.4307.2, in lateral view (A1), early whorls in lateral view (A2), detail of whorl face with selenizone (slit-band) on crest in lateral view (A3). B. MB.Ga.4304.1, in lateral view (B1), early whorls including smooth protoconch in lateral view (B2), early whorls including smooth protoconch in oblique lateral view (B3).