Provanna alexi, Amano & Little, 2014
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publication ID |
https://doi.org/ 10.4202/app.2012.0002 |
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persistent identifier |
https://treatment.plazi.org/id/7216697D-FFE1-030B-FCC1-96A4B8F94C93 |
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treatment provided by |
Felipe |
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scientific name |
Provanna alexi |
| status |
sp. nov. |
Provanna alexi View in CoL sp. nov.
Fig. 3 View Fig .
2005 Provanna sp. ; Amano and Little 2005: figs. 5H–K.
Etymology: Named for the second author’s son Alex.
Type material: Holotype, JUE 15904 ( Fig. 3A View Fig ); Paratypes, JUE 15905- 1 ( Fig. 3B View Fig ), JUE 15905-2 ( Fig. 3C View Fig ), JUE 15905-3 ( Fig. 3D View Fig ).
Type locality: 5.5 km upstream of Shosanbetsu Village on the Setakinai River in northwestern Hokkaido, Japan (see Amano and Little 2005); whale-fall site .
Type horizon: Fossil whale-fall deposits of the Chikubetsu Formation, lower Middle Miocene .
Dimensions.—See Table 3.
Diagnosis.—Small-sized Provanna with strong, tabulated shoulder, 8–16 spiral cords and 22–26 axial ribs on body whorl.
Description. —Shell small, up to 6.5 mm high, with ovate fusiform shape; teleoconch with three whorls; protoconch not preserved. Sutures weakly impressed. Apical whorls sculptured by strong spiral cords, three to six in number on penultimate whorl, and strong, straight axial ribs, six to twenty-one in number on penultimate whorl. Very distinct angular shoulder formed by strong spiral cord with strong nodes at intersection with axial ribs. Narrow sutural ramp adapically of shoulder. Whorl sides ranging in shape from nearly straight to weakly curved. Stronger spiral cords causing distinct angulations in body whorl sides of some specimens. Body whorl large, comprising roughly 60–70% of shell height. Ornamentation on body whorl weaker than on apical whorls, with eight to sixteen spiral cords, best developed near shoul- der and whorl base, and twenty-two to twenty-six axial ribs.
2
3
Shoulder also weaker on body whorl and sutural ramp having greater slope angle. Aperture ovate with suggestion of weak apertural notch. Shells formed of two distinct microstructural elements: inner crossed lamellar layer (up to 120 μm thick) and outer simple prismatic layer (up to 20 μm thick).
Remarks. —In having a tabulate shoulder, Provanna alexi is similar to P. antiqua from Eocene wood-falls and Eocene to Oligocene seep deposits in Washington State, USA and P. marshalli from Miocene seeps of New Zealand. However, P. antiqua differs from P. alexi by having less numerous spiral cords on the body whorl (2–7 in P. antiqua ; 8–16 in P. alexi ). The number of spiral cords in P. marshalli (0–11) is generally less than in P. alexi , but there is some overlap. In addition, axial ribs are always present in P. alexi , whereas this character is lacking in some specimens of both P. antiqua and P. marshalli .
Stratigraphic and geographic range. —From the type locality only.
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