Altaspiratella bearnensis ( Curry, 1982 )

Cotton, Laura J., Janssen, Arie W., Pearson, Paul N. & Driel, Rens van, 2017, Pteropoda (Mollusca, Gastropoda, Thecosomata) from the Eocene / Oligocene boundary interval of three cored boreholes in southern coastal Tanzania and their response to the global cooling event, Palaeontologia Electronica 20 (3), pp. 1-21 : 4-5

Altaspiratella bearnensis ( Curry, 1982)

Figure 2.1-2

* v 1982 Plotophysops bearnensis Curry , p. 40, pl. 1, figure 9a-c.

v. (1986) Spiratella tutelina Curr. – Merle, p. 43 (non Curry).

v. 1990 b Altaspiratella bearnensis (Curry 1981) – Janssen, p. 68.

? 1992 Altaspiratella bearnensis (Curry) – Hodgkinson et al., p. 13, pl. 1, figures 1-2.

. (1996) Altaspiratella bearnensis (Curry, 1981) – Kunz, p. 164, pl. 30, figures 1-3.

v. 2010 Altaspiratella bearnensis ( Curry, 1982) – Cahuzac and Janssen, p. 24, pl. 2, figures 1-4, pl. 3, figure 1.

v. 2013 Altaspiratella bearnensis – King et al., p. 192, 193.

Material examined. TDP 12.28.1, 66-76 cm, depth 90.91-91.01 m below surface, composite depth 148.91-149.01 m; RGM 777374 (1 specimen, Figure 2.1-2 , H = 1.36, W = 0.80 mm) .

Description. Only available specimen with high conical shell, 1.7 times higher than wide, and apical angle of c. 40°. Four and a half slightly convex and comparatively high whorls, regularly increasing in diameter and separated by incised, oblique suture. Whorls attach below periphery of preceding whorl. Specimen incomplete, last whorl missing, in shell preservation, but filled with pyrite.

Discussion. Two closely resembling Altaspiratella species are currently known. Altaspiratella elongatoidea ( Aldrich, 1887) occurred during the earliest Eocene (Ypresian, nannoplankton Zones NP 9 and 10) of the USA ( Hodgkinson et al., 1992; Janssen et al., 2016); A. bearnensis ( Curry, 1982) , introduced from the Ypresian (zone NP 12/13) of SW France, is also known from the USA (with some doubt) in rocks of middle Eocene, Lutetian age (Zone NP 15). These two species differ only very slightly in the proportions of their early whorls. Of A. elongatoidea no specimens preserving apertural structures are known, so there might be differences in that respect as well.

In the single available specimen from Tanzania apertural structures are missing, and its apical whorls take a position in between the two known species mentioned above. This could be an indication that these two taxa represent a single, longranging species. However, as long as apertural structures cannot be compared it seems better to keep them apart and the one available Tanzanian specimen is here considered, for the time being, to be the youngest representative of the A. elongatoidea - A. bearnensis lineage. The specimen extends the vertical range to the Priabonian (Zones P 16-17, NP 19-20; Nicholas et al., 2006, figure 16).

Figures

FIGURE 2. Altaspiratella bearnensis (Curry, 1982); RGM 777374; 1: apical view, 2: apertural view. Bar equals 100 μm.