Jeanclaudella, Monari & Conti, 2025

Genus Jeanclaudella nom. nov.

Zoobank LSID: urn:lsid:zoobank.org:act:

pro Aaleniella Conti & Fischer, 1981 View in CoL non Plumhoff, 1963

Type species. Aaleniella umbriensis Conti & Fischer, 1981 . Umbria ( Central Apennine , Italy), lower Bajocian, Stephanoceras humpriesianum Zone .

Derivation of name. Dedicated to Jean-Claude Fischer (1930–2009), late palaeontologist of the Muséum National d’Histoire Naturelle (Paris, France) who greatly contributed to the knowledge of the Jurassic palaeontology, early tutor of one of the present authors (MAC) and co-author of the genus Aaleniella View in CoL .

Original diagnosis ( Conti & Fischer 1981, p. 141). Shell trochiform. Spire elevated. Whorls flat or slightly concave. Last whorl occupying 2/3 of the total height, subcarinated at the periphery. Ornament of collabral costellae, possibly increased by spiral arrangements. Aperture suborbicular, holostomatous; outer lip moderately prosocline; columellar lip unthickened, scarcely curved. Umbilicus very narrow, without margin.

Emended diagnosis. Shell trochiform, few millimetres high, with conoidal to distinctly cyrtoconoidal outline. Early whorls well-rounded. Surface of adult whorls concave. Last whorl representing about 70% of shell height. Periphery angulated and carinate, placed just above suture. Base slightly convex, to moderately inflated and with narrow umbilicus. Aperture rounded-quadrangular. Peristome with thin parietal inductura. Columellar lip slightly arched and simple. Early whorls bearing evenly distributed, prosocline and opisthocyrt collabral riblets. Adult whorls ornamented by prosocline ribs/riblets forming nodes along subsutural band and on peripheral keel. Collabral ornament attenuating or vanishing on median part of whorl surface during growth. Base with spiral threads/cords.

Remarks. The genus was assigned to the subfamily Margaritinae Thiele, 1924 by Conti & Fischer (1984), a taxon currently considered of family rank within the superfamily Trochoidea Rafinesque, 1815 ( Bouchet et al. 2017). However, the rounded earliest teleoconch whorls sculptured by a regular pattern of collabral ribs indicate that Jeanclaudella nom. nov. belongs to the superfamily Eucycloidea Koken, 1896 . Members of the family Eucyclidae Koken, 1896 are charaterized by the appearance of a single spiral keel on the abapical part of the whorls on the earliest teleoconch whorls (in addition to axial ribs), which commonly changes into an angulate and carinate periphery on the subsequent whorls ( Gründel 2007; Szabó et al. 2019). Another spiral element, less prominent than the peripheral keel, can appear near the adapical suture. The appearance of this spiral ornament in Jeanclaudella , though late during the early ontogeny, suggests that this genus belongs to Eucyclidae . Moreover, in Jeanclaudella the peristome is discontinuous and provided only with a thin inductura on the parietal lip. According to Bandel (2010), the discontinuity of the peristome is another distinctive aspect of this family.

Within the Eucyclidae , Jeanclaudella shows the closest similarity to Mistelgauia Schulbert & Nützel, 2013 , especially in the pattern and ontogeny of the main elements of the ornament. A small umbilicus is also present in those species previously ascribed to Tylotrochus Koken, 1896 by Gründel (1999) and Gründel et al. (2011) and subsequently moved to Mistelgauia by Schulbert & Nützel (2013). Jeanclaudella differs from Mistelgauia in having a trochiform shell. The shell of Mistelgauia is more globose, with a much higher and distinctly inflated base. Moreover, the base has a reticulate ornament of spiral cords and regularly spaced collabral threads. This ornament pattern is quite frequent in the eucycloideans and is considered as a diagnostic character of Mistelgauia by Schulbert & Nützel (2013), but it is absent in Jeanclaudella .

The protoconch of Jeanclaudella , is preserved only in Jeanclaudella variata ( Conti & Fischer, 1981) (see below), which is not the type species. In J. variata , the protoconch is much more prominent than in Mistelgauia and makes the apex submamillate. The characters of the peristome of the type species of Mistelgauia are unknown, but M. raresculptata shows an aperture which is much wider and rounded than in Jeanclaudella . Based on the outline of the last whorl and the inflated base, a similar shape of the aperture is most probably shared also by the type species. Furthermore, in M. raresculptata the inner lip is thickened and bears a narrow crescent-shaped furrow, whereas in Jeanclaudella it is thin and simple.

All the three species of Jeanclaudella show concave adult whorls. In the type species of Mistelgauia , Mistelgauia monarii Schulbert & Nützel, 2013 (p. 734, figs 9A–I cum syn.), and in the other species assigned to this genus by Schulbert & Nützel (2013), namely Mistelgauia raresculptata ( Gründel, 1999) (p. 632, pl. 2, figs 2–7), the surface of the adult whorls is flat to slightly convex. However, in Calliotropis ( Riselloidea) faustiankensis Ferrari & Kaim, 2018 (p. 7, figs 3K–N, 5A–L), a species clearly belonging to Mistelgauia , the adult whorls are concave.

The close similarity between Mistelgauia and Jeanclaudella could also suggest subgeneric relationships. In this case, the differences could reflect the different stratigraphical distribution and the paleobiogeographical disjunction of these taxa. Indeed, the species of Mistelgauia come from deposits of the European epicontinental shelf: the type species from the Toarcian/Aalenian transition of Franconia (southern Germany), M. rarescuptata from the upper Pliensbachian of Grimmen (northern Germany) and M. faustiankensis from the middle Bathonian of Poland. In contrast, the species of Jeanclaudella are known until now only from the Bajocian pelagic sediments of the central part of western Tethys.

Jeanclaudella shares with Riselloidea Cossmann, 1909 View in CoL , Biarmatoidella Gründel, 2003 and Paleunema Kittl, 1891 View in CoL the trochiform shape of the shell, the concave adult whorls, the presence of a peripheral angulation running just above the suture, and the adult ornament pattern of collabral ribs forming a row of nodes or granulations just below the suture and at the intersection with the peripheral carina.

Kaim (2004) considered Riselloidea View in CoL as junior synonym of Calliotropis Seguenza, 1902 View in CoL . Ferrari et al. (2014) and Ferrari & Kaim (2018) argued that there are no compelling reasons to keep them separate as well. However, they preferred to treat Riselloidea View in CoL as an arbitrary temporal subgenus of Calliotropis View in CoL due to its markedly different stratigraphic distribution. These authors interpreted Calliotropis View in CoL in a very extensive way and assigned numerous Jurassic and Cretaceous species to Calliotropis ( Riselloidea) , including those previously ascribed to Biarmatoidella and, possibly, to the Late Triassic genus Trochonodus Nützel et al., 2003 View in CoL . In contrast, the cladistic analysis performed by Pérez et al. (2022) demonstrates that both Riselloidea View in CoL and Trochonodus View in CoL represent clades distinct from Calliotropis View in CoL . Based on the type species of Riselloidea View in CoL , namely Risellopsis subdisjuncta Cossmann, 1907 (p.59, pl. 2, figs 10–12; Cossmann 1916, p. 127, pl. 4, 14–15; see also the online catalogue of the Muséum National d’Histoire Naturelle, Paris, France, https://science.mnhn.fr, accessed May, 2025), Riselloidea View in CoL differs from Jeanclaudella in the anomphalous and flat base and in the presence of a smooth callus which strengthens the columellar lip and extends towards the axial region of the base ( Cossmann 1907, 1916).

As far as Biarmatoidella is concerned, the results of the cladistic analysis by Pérez et al. (2022) are ambiguous. They show that the type species, Biarmatoidella biarmata (Münster in Goldfuss, 1844) (p. 55, pl. 180, fig. 2; Ferrari & Kaim 2018, p. 5, figs 3A–J cum syn.) and Riselloidea vierowiensis Gründel, 2000 (p. 230, pl. 6 figs 16–17; Gründel 2003b, p. 153, pl. 5, figs 6–7) form the sister-group of R. subdisjuncta . According to these authors, this indicates that Biarmatoidella belongs to the Riselloidea clade and is a junior synonym of Riselloidea , as was also suggested by Kaim (2004), Bandel (2010), Ferrari et al. (2014), and Ferrari & Kaim (2018). However, as remarked also by Pérez et al. (2022), R. vierowiensis could be alternatively considered a species of Biarmatoidella and the possible inclusion into the analysis of other species, such as Biarmatoidella lorioli ( Greppin, 1898) (p. 48, pl. 5, figs 5–7; Gründel 2003a, p. 65, pl. 6, figs 9, 10) could reveal that this genus is monophyletic and sister-group of Riselloidea . Whatever the taxonomic status of Biarmatoidella is, its type species is not congeneric with the species of Jeanclaudella . It differs in the absence of an umbilicus and in the stout columellar lip provided with a wide and excavated crescent-shaped callus.

Paleunema View in CoL , a genus recently revised by Karapunar & Nützel (2021, p. 123, fig. 77), is anomphalous and ornamented by distinctly sinuous collabral ribs which form prominent, scaly and hollow nodes on the peripheral keel. Furthermore, a weak spiral cord runs in the upper half of the whorl surface. The collabral ribs make nodes at intersection with this cord where they become bifurcated. The same characters making Jeanclaudella similar to the genera mentioned above are present also in Eunemopsis Kittl, 1891 , type genus of the eucycloidean family Eunemopsidae Bandel, 2010 View in CoL . However, the lamellar spiral ridge on the columellar lip which characterizes the members of this family ( Bandel 2010) is absent in Jeanclaudella .