Paskentana, Kiel, K. A. Campbell, C. Elder & C. Little, 2008
|
publication ID |
https://doi.org/ 10.4202/app.2008.0412 |
|
persistent identifier |
https://treatment.plazi.org/id/03DC9B54-FFEC-3371-FC85-47D57CD7CBBF |
|
treatment provided by |
Felipe |
|
scientific name |
Paskentana |
| status |
|
Genus Paskentana View in CoL nov.
Etymology: After the type locality near Paskenta in California, USA.
Type species: Turbo paskentaensis Stanton, 1895 ; Upper Jurassic to Lower Cretaceous, Paskenta, California, USA .
Diagnosis.—Adult shell littoriniform, of moderate size, very thin−shelled, whorls convex or shouldered, bearing mainly spiral sculpture with minor axial elements on whorl’s shoul− der; spirals smooth, tuberculate, or spinose; juvenile whorls with mostly smooth spiral sculpture only; aperture oval, apical side somewhat pointed; inner lip smooth and may have callus; growth lines mostly straight but may be somewhat sinuous on shoulder.
Discussion.—At the Bear Creek site (site 4) we found a fragment of a single isolated larval shell ( Fig. 6E View Fig ) consisting of one whorl that is 350 µm wide and is sculptured by collabral ribs and spiral cords. Larval shells of this size and sculpture are known from provannids, abyssochrysids and the recently established hokkaidoconchids ( Warén and Bouchet 1993; Kaim et al. 2008). Paskentana paskentaensis occurs in rockforming masses at the Bear Creek site (see Fig. 3A View Fig ) and thus we find it most likely that this isolated larval shell belongs to this gastropod species. Kaim et al. (2008) considered the “decollate” protoconch of provannids as the distinguishing feature to hokkaidoconchids: juvenile provannids apparently seal the base of their protoconch with a plug of calcium carbonate, above which the shell typically is not preserved ( Kaim et al. 2008). Thus our isolated larval shell is insufficient to distinguish between the two groups. Hokkaidoconchids and abyssochrysids both have very elongate, high−spired shells ( Houbrick 1979; Kaim et al. 2008), whereas certain provannids have rather globular shells, namely the genera Alviniconcha Okutani and Ohta, 1988 and Ifremeria ( Okutani and Ohta 1988; Bouchet and Warén 1991). In addition, provannids have similar sculpture on the early whorls. Among the provannid genera, Provanna and Desbruyeresia Warén and Bouchet, 1993 differ from Paskentana by having fewer spiral cords per whorl, and by being not as strongly shouldered as some of the Paskentana specimens. Alviniconcha Okutani and Ohta, 1988 is quite close to Paskentana regarding shell shape; the sculpture on the first whorls of Alviniconcha tends to be more tuberculate than in the juvenile shell of Paskentana paskentaensis ; the suture is less distinct in Alviniconcha and the whorl is also not shouldered, as are whorls of some specimens of Paskentana . Adult Ifremeria develop a notch in the adapical part of the aperture that results in a scaly subsutural ridge on the whorls, which is not seen in Paskentana . Early whorls of Ifremeria are more angular and have stronger spirals with stronger tubercles ( Warén and Bouchet 1986; Warén and Ponder 1991; Warén and Bouchet 1993). In sum, we place Paskentana in the superfamily Abyssochrysoidea . Better preserved material is needed to clarify its position at the family level.
One genus and species that is potentially related to Paskentana is Elmira cornuartietis Cooke, 1919 from a presumably Oligocene seep deposit in Cuba ( Cooke 1919; Kiel and Peckmann 2007). It resembles Paskentana in its general shell shape but is more lower spired than even the globular Paskentana globosa sp. nov., and has coarse, undulating spiral sculpture which we have not seen in any of our Paskentana species.
Several gastropod groups build adult shells similar to those of Paskentana , for example certain Purpurinidae or Eucyclidae . Juvenile eucyclids have a very broad apical angle and evenly convex whorls that are sculptured by distinct axial ribs (see Kiel and Bandel 2001; Kaim 2004). Thus, they are quite unlike the juvenile shell of Paskentana , which has an angulation in the lower half of the whorl and shows spiral ornament only. Juveniles of Purpurina have strongly angulate whorls with the angulation in the upper half of the whorl, and strong axial sculpture with only minor spirals (Kaim 2004). Therefore the juvenile shell of Purpurina also is very different from that of Paskentana . In addition to this, the missing tip of the Paskentana paskentaensis specimen shown on Fig. 5F View Fig is 600 µm wide. This would be wide enough to accommodate a eucyclid (or vetigastropod) protoconch, which usually does not exceed 400 µm in width ( Bandel 1982). Purpurinid larval shells, however, are 1000 to 1500 µm in diameter (Kaim 2004) and thus too wide to fit onto the missing tip, although lecithotrophic protoconchs might have been smaller. Similar shells are also known from members of the intertidal caenogastropod families Planaxidae Gray, 1850 , and Littorinidae Gray, 1840 , and from the deep−water family Provannidae Warén and Ponder, 1991 . Planaxids and littorinids have ornamentation on the early teleoconch that is very similar to that seen in P. paskentaensis , and their protoconchs do not exceed 300 µm in width and would thus fit onto the missing tip of P. paskentaensis ( Houbrick 1987; Reid 1996; Reid 2004).
Stratigraphic and geographic range.—Tithonian (Upper Jurassic) to Hauterivian (Lower Cretaceous), Great Valley Group and Franciscan Accretionary Complex, California, USA.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.