Itieroptygmatis cylindrata, Gründel & Keupp & Lang & Nützel, 2022

Gruendel, Joachim, Keupp, Helmut, Lang, Fritz & Nuetzel, Alexander, 2022, Late Jurassic (Upper Kimmeridgian) Heterobranchia (Gastropoda) of the coral-facies of Saal near Kelheim and the viciniy of Nattheim (Germany), Zitteliana 96, pp. 179-221 : 179

Itieroptygmatis cylindrata sp. nov.

Plate 18: figs 1-14

?1882 - Itieria austriaca Zitt. - Schlosser: 84, pl. 12, figs 8, 9.

2017 - Nerineoidea Nr. 9a, b - Gründel: 33, pl. 15B-C.

Derivatio nominis.

Latin cylindratus - cylindrical; according to the approximately cylindrical shell shape of the late teleoconch of this species.

Holotype.

SNSB-BSPG 2021 XV 80, collection Lang.

Locus typicus.

Saal Quarry near Kelheim.

Stratum typicum.

Upper Kimmeridgian.

Paratypes.

45 specimens from Saal (43 specimens collection Lang, BSPG (SNSB-BSPG 2021 XV 81-84, 86, 109-146); one specimen collection Keupp, SNSB-BSPG 2021 XV 87, one specimen collection Schäfer, BSPG SNSB-BSPG 2021 XV 85; additional specimens on block with Cassianopsis quenstedti SNSB-BSPG 2015 VII 58.

Material.

A total of 56 specimens from Saal, 46 types (see above) and 10 specimens without type status from private collections: 6 specimens collection Lang, 4 specimens collection Schäfer.

Diagnosis.

The adapical part of the shell is slender with many whorls lacking a ramp. Later whorls are broad in relation to their height and have a ramp which becomes broader from whorl to whorl in most specimens. Below the ramp, a weak concavity (lateral view) is developed; rarely, the ramp remains narrow and the concavity is lacking. The last whorls of large specimens increase only slowly in width and this part of the shell is more or less cylindrical. The transition from whorl face to base is evenly rounded without edge or spiral cord. Aperture with two columellar and palatal plaits and one parietal plait.

This species is present in two morphotypes and specimens that are intermediate:

Morphotype 1: Plate 18 : figs 1-10;

Transition from morphotype 1 to morphotype 2: Plate 18 : fig. 11;

Morphotype 2: Plate 18 : figs 12-14.

Description.

A large specimen (early whorl missing) is 33 mm high. The early shell is very slender consisting of at least eight smooth whorls having a weakly convex whorl face and somewhat impressed sutures. The following 2-3 whorls increase rapidly in width and are very wide in relation to their height. As a result, the spire is coeloconoid. In the mentioned 2-3 whorls following the slender spire whorls, a broad, distinctly concave, funnel-shaped ramp is formed. From now on, the ontogenetic evolution of the shell follows different pathways leading to two varieties (morphotype 1 and 2 as well as to intermediate forms).

In morphotype 1 (much more abundant than morphotype 2), the wide ramp continues and becomes wider. It is delimited from whorl face by a broad concavity with indistinct borders. Initially, the whorls continue to rapidly increase in width. In large, more or less fully grown specimens, the increase in width decelerates, the last whorls are high and almost cylindrical in shape. The edge of the ramp is projecting abaxially and forms the whorl periphery.

In the other extreme form, morphotype 2, the rapid increase of the width of the whorls and the formation of a broad ramp is confined to 2-3 whorls. Afterwards, the whorls become wider and increase in width only slowly, but considerably increase in height. The ramp forms only a narrow band. The whorl face is straight and lacks a concavity below the ramp so that this part of the shell is almost cylindrical. As mentioned, there are transitional forms between varieties 1 and 2 (Plate 18 : fig. 11).

All individuals have a continuous, rounded transition from whorl face to the strongly convex base. Base and whorl face are smooth. The base has a distinct umbilicus. The growth lines run straight and somewhat opisthocline on the whorl face and curve strongly backward below the ramp. The aperture is very narrow, adapically acute and has a weakly developed siphonal canal. The inner lip is broadened and detached in the columellar area; it partly covers the umbilicus. The inner lip bears a strong parietal and two columellar plaits. The adapical columellar plait is weaker than the abapical one. The aperture has two palatal plaits which are, however, rarely recognizable.

Remarks.

Itieria austriaca Zittel as described by Schlosser (1882) closely resembles morphotype 2 of Itieroptygmatis cylindrata sp. nov. However, it has a distinctly lower last whorl in relation to its spire height. The real Itieria austriaca Zittel, 1873 differs distinctly from Itieroptygmatis cylindrata sp. nov. by lacking a ramp and by having a subsutural row of knobs.

Relationships.

Itieria (Campichia) pellati Cossmann and Itieria (Campichia) truncata Pictet and Campiche, both sensu Cossmann (1916), resemble morphotype 1 of Itieroptygmatis cylindrata sp. nov. However, their spire is lower and has not as many whorls, the last whorl is much broader than the spire (having wide ramp only on a single whorl). Itieria obtusiceps Zittel, 1873 resembles morphotype 2 of Itieroptygmatis cylindrata. However, I. obtusiceps has a less distinct ramp, the spire is blunter, and the shell outline is more oval-shaped. Phaneroptyxis nogreti Guir. and Ogérien sensu Cossmann (1898) differs from morphotype 1 of Itieroptygmatis cylindrata sp. nov. by having a lower last whorl (in relation to spire height) in large specimens, lacking a wide ramp, and not having a cylindrical shape of the last whorl.

Figures

Plate 18. (1 - 10) Itieroptygmatis cylindrata sp. nov., morphotype 1. (1 - 2) Holotype, SNSB-BSPG 2021 XV 80, Saal (collection Lang); (1) lateral view, height 15 mm; (2) oblique view, width 5.5 mm (Gruendel 2017, fig. 15 B). (3 - 4) Paratype, SNSB-BSPG 2021 XV 81, Saal (collection Lang), apical and lateral views, width 14 mm. (5 - 6) Paratype, SNSB-BSPG 2021 XV 82, Saal (collection Lang), apical and lateral views, width 16 mm (original Gruendel 2017, fig. 15 C). (7 - 8) Paratype, SNSB-BSPG 2021 XV 83, Saal (collection Lang), basal and lateral views, width 15 mm. (9 - 10) Paratype, SNSB-BSPG 2021 XV 84, Saal (collection Lang); (9) columellar section, height 16 mm; (10) detail of (9), height 7.5 mm. (11) Itieroptygmatis cylindrata sp. nov., transition from morphotype 1 to morphotype 2, paratype, SNSB-BSPG 2021 XV 85, Saal (collection Schaefer), lateral view, height 33 mm. (12 - 14) Itieroptygmatis cylindrata sp. nov., morphotype 2, paratype, SNSB-BSPG 2021 XV 86, Saal (collection Lang), (12) lateral view, height 27 mm; (13) apex in lateral view, height 12 mm; (14) apical, width 13 mm. (15 - 16) Itieroptygmatis sp. 1. (15) SNSB-BSPG 2021 XV 88, Saal (collection Lang), lateral view, height 47 mm. (16) SNSB-BSPG 2021 XV 89, Saal (collection Lang), base, width 21 mm.