Eotebenna viviannae Peel, 1991a

Peel, John S. & Berg-Madsen, Vivianne, 2023, Muscle attachment scars in helcionelloids from Denmark cast light on mollusc evolution in the Cambrian, Acta Palaeontologica Polonica 68 (4), pp. 625-638 : 627-629

Eotebenna viviannae Peel, 1991a

Figs. 2 , 3 .

1985 rostroconch sp. I; Berg-Madsen 1985: fig. 5D.

1991 Eotebenna viviannae sp. nov.; Peel 1991a: 173, fig. 19.

1991 Eotebenna viviannae ; Peel 1991b: fig. 31.

1997 Eotebenna cf. viviannae ; Hinz-Schallreuter 1997: pl. 2: 4.

2004 Eotebenna viviannae ; Gubanov et al. 2004: 10, fig. 8.

2004 Eotebenna viviannae ; Peel 2004: fig. 1C.

2006 Eotebenna viviannae ; Peel 2006: text-fig. 2H.

2021 Eotebenna viviannae ; Peel 2021c: fig. 1H.

Type material: Holotype MGUH 19564 , well preserved shell internal mould ( Fig. 2 ) . Paratypes: MGUH 19565 and three additional internal moulds ( MGUH 19566–19568 ), that were described by Peel (1991a: fig. 19H–N) but are not figured herein. All from type locality and horizon. Type locality: The rivulet Øleå, Bornholm, Denmark .

Type horizon: Andrarum Limestone, Guzhangian, Miaolingian, middle Cambrian.

Material.— MGUH 34273–34276 , internal moulds from type locality and horizon .

Description.—Apical attachment scars and fibrous shell microstructure are added to the description of Peel (1991a).

Remarks.— Eotebenna viviannae was described by Peel (1991a) on the basis of exfoliated specimens and internal moulds without details of external ornamentation from the Andrarum Limestone of Bornholm, Denmark. The shell is characteristically elongate and laterally compressed ( Figs. 2 , 3 ). Its overall shape is similar to that of the Ordovician rostroconch Pinnocaris lapworthi Etheridge, 1878 , but the growth vectors are dissimilar ( Peel 2004). A well preserved specimen clearly showing the comarginal growth lines on the elongate shell was illustrated by Hinz-Schallreuter (1997) and similar ornamentation is retained in a partially exfoliated specimen (MGUH 34273) illustrated here ( Fig. 3B ). In addition to material from Bornholm, ten silicified specimens of Eotebenna viviannae were described by Gubanov et al. (2004) from the Kuonamka Formation (Drumian, Miaolingian) of northern Siberia, Russia.

In terms of its elongate shape, Eotebenna viviannae is similar to the type species Eotebenna pontifex Runnegar and Jell, 1976 , from the Currant Bush Limestone (Miaolingian) of Queensland, Australia but the latter is distinguished by its massive, circular snorkel at the sub-apical margin when compared to the inverted teardrop-shaped sub-apical opening in Eotebenna viviannae ( Fig. 2A 4 ).

Stratigraphic and geographic range.—Drumian of Siberia, Russia and Guzhangian of Denmark (both middle Cambrian).

Figures

Fig. 2. Helcionelloid mollusc Eotebenna viviannae Peel, 1991a, MGUH 19564, holotype, internal mould, Andrarum Limestone, Bornholm, Denmark, Guzhangian, Miaolingian, middle Cambrian.A1. Oblique lateral view showing margin of shell (arrow) along the narrow slit joining the sub-apical and supra-apical apertures.A2. Oblique apico-lateral view.A3. Lateral view.A4. Oblique view showing inverted teardrop-shaped sub-apical aperture and irregular area (arrow) of possible muscle scar.A5. Lateral view of apex.A6. Oblique lateral view of apex showing radial fibrous structure beneath smooth outer layer.

Fig.3. Helcionelloid mollusc Eotebenna viviannae Peel, 1991a, internal moulds,Andrarum Limestone, Bornholm,Denmark,Guzhangian, Miaolingian, middle Cambrian. A. MGUH 19565, paratype, lateral view (A1) with detail of apex (A2). B. MGUH 34273, lateral (B1) and apico-lateral views showing impression of comarginal ornamentation and cylindrical form of median sub-apical area (B2). C. Specimen lost, lateral view (C1) with detail of apex (C2), arrow locates detail of shell structure (C3). D. MGUH 34274, lateral view with detail of radial fibrous structure and overlying imbricated lamellae (D2), and patch of ornamented outer shell (D1, arrow). E. MGUH 34275, lateral view with detail of apex (E2) with muscle scars; arrows locate possible muscle scar. F. MGUH 34276, lateral view (F1) with detail of possible muscle scar (F2) located by arrows.

Fig. 4. Helcionelloid mollusc Eotebenna danica sp. nov., internal moulds, Andrarum Limestone, Bornholm, Denmark, Guzhangian, Miaolingian, middle Cambrian. A. MGUH 34277, lateral view (A1) with rectangles indicating location of Fig. 5B1, B2, and B3. Muscle scars at apex illustrated in different orientations (A2–A6), with arrow in A2 indicating slight diagenetic compression or deformation along edge of muscle field.Arrow in A3 indicating imbricated lamellar structure shown in detail in A4. B. MGUH 34278, apex in lateral view. C. MGUH 34279, lateral view. D. MGUH 34280, holotype, lateral (D1) and apico-lateral (D2) views, the latter showing the laterally compressed shell form, with detail of apical muscle scars (D3). E. MGUH 34281, lateral view. F. MGUH 34282, apex in lateral view. pontifex Runnegar and Jell, 1976, from the Currant Bush southern Freuchen Land, North Greenland is more strongly Limestone (Miaolingian) of Queensland, Australia, is also coiled than Eotebenna danica, with a convex supra-apical much more elongate than Eotebenna danica but the massive surface, in lateral view, and the apex strongly overhanging snorkel is circular in cross-section compared to the inverted the sub-apical surface (Peel 1989, 1991b). teardrop-shape in the two Bornholm species. Eotebenna arctica Peel, 1989, from the Henson Gletscher Stratigraphic and geographic range.—Drumian of Sweden Formation (uppermost Series 2, Stage 4, lower Cambrian) of and Guzhangian of Denmark (both middle Cambrian).