Tianzhushanella tolli, Kouchinsky & Bengtson & Landing & Steiner & Vendrasco & Ziegler, 2017

Kouchinsky, Artem, Bengtson, Stefan, Landing, Ed, Steiner, Michael, Vendrasco, Michael & Ziegler, Karen, 2017, Terreneuvian stratigraphy and faunas from the Anabar Uplift, Siberia, Acta Palaeontologica Polonica 62 (2), pp. 311-440 : 386

publication ID	https://doi.org/ 10.4202/app.00289.2016
persistent identifier	https://treatment.plazi.org/id/03AD87A8-FFD0-6D6C-FCB9-FF2965A58570
treatment provided by	Felipe
scientific name	Tianzhushanella tolli
status	sp. nov.

Treatment

Tianzhushanella tolli sp. nov.

Fig. 49 View Fig .

Etymology: Named for Siberian Arctic explorer Eduard Gustav von Toll (1858–1902).

Type material: Holotype: SMNH X5839 View Materials ( Fig. 49A View Fig ) and paratype: SMNH X5840 View Materials ( Fig. 49B View Fig ), collected by Vladimir V. Missarzhevsky.

Type locality: 70°42’34’’ N, 112°47’58’’ E, locality M314 (Rozanov et al. 1969; Fig. 1) on the right bank of the Fomich River , ca. 6 km upstream from the Afanas’ev Lakes, northwestern flank of the Anabar Uplift GoogleMaps .

Type horizon: Medvezhya Formation, variegated limestones with glauconite, 7 m above the top of the Nemakit-Daldyn Formation, sample M314/7 (see Rozanov et al. 1969: 44, fig. 9). Correlated herein with the Fortunian‒Cambrian Stage 2 transitional beds.

Material.—The species is known at present only from the type series.

Diagnosis. —Species of Tianzhushanella characterized by shells with a median septum that subdivides the apex into two broad halves that face each other.

Description.—Bilaterally symmetrical shell with broad, oval, nearly circular aperture and with apex which overhangs subapical margin. Subapical margin of the aperture gently concave, broadly and slightly arched (as replicated on the internal moulds). Inner surface of the mould of the apical area is subdivided into two bilaterally symmetrical lobes separated by a broad, median depression that arises at the subapical side ( Fig. 49A View Fig 3, B 2), crosses the umbo ( Fig. 49A View Fig 1, B 1) and becomes obsolescent on the supra-apical side. Two lateral shallow linear depressions on the mould originate at the subapical margin of the aperture, diverge at ca. 30° to cross lateral parts of the mould, and become obsolescent before reaching the supra-apical margin of the aperture. The apical part and median zone of the mould are covered with an aciculate texture ( Fig. 49A View Fig 1).

Remarks.—The new species differs from other forms of Tianzhushanella and Lathamella in having the apex subdivided into two broad halves by a longer and narrower, median, linear septum (furrow on internal moulds). Other named species of the two genera have smaller umbonal cavities with a relatively broader median depression.

Stratigraphic and geographic range.— Type locality and horizon only.