Neritodryas Martens, 1869,

Symonds, Malcolm Francis & Pacaud, Jean-Michel, 2010, New species of Neritidae (Neritimorpha) from the Ypresian and Bartonian of the Paris and Basse-Loire Basins, France, Zootaxa 2606, pp. 55-68: 60-62

publication ID 10.5281/zenodo.197721

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Neritodryas Martens, 1869


Genus Neritodryas Martens, 1869 

Type species. By subsequent designation, Baker (1923: 153): Nerita cornea Linné 1758  . Recent, freshwater, Indopacific.

Diagnosis. Moderately large, up to 40 mm in height, spire blunt, labial area smooth, a blunt tooth below, often with small teeth on septum edge, operculum ribbed. (Amended after Keen 1960).

Remarks. Martens (1869), when erecting Neritodryas  , placed within it the two Recent species N. cornea ( Linné, 1758)  and N. dubia ( Gmelin, 1791)  . Subsequently ( Martens 1879) he covered Neritodryas  in greater detail and included two additional species N. chimmoi ( Reeve, 1856)  and N. subsulcata ( Sowerby, 1836)  . He described the columellar edge of Neritodryas  as being without teeth but specimens of all four of these species commonly have small columellar teeth (pers. obs.). Accordingly Marten’s diagnosis is incorrect in this respect and we have amended the above diagnosis to include a reference to small teeth on the septum edge. All the Recent species have spiral ridges on the teleoconch except for N. dubia  , which is smooth, apart from fine collabral growth lines. The genus is unusual within Neritidae  in that the Recent species live mainly on trees and bushes beside freshwater and in mangrove swamps ( Cowie & Smith 2000). The ontogeny of Neritodryas  is not fully known. Kano (2006) considered that the considerable intraspecific variation in the size of the opercular nucleus  might suggest nonplanktotrophic development. Holthuis (1995) took the view that Neritodryas  species have short-lived, possibly non-feeding (lecithotrophic) pelagic larvae as, firstly, the protoconch size is intermediate between planktotrophic veligers of Neritina  and Clithon  and those of benthic Fluvinerita  and, secondly, their geographic distribution is extensive enough to imply pelagic larvae even though more limited than ranges of typical Neritina  and Clithon  .

Neritodryas guillioui  sp. nov. ( Figs 4–5View FIGURES 1 – 4. 1View FIGURES 5 – 8. 5)

Type material. Holotype MNHN A 31490View Materials (Faullummel coll., Fig. 4View FIGURES 1 – 4. 1 a –c); one paratype MNHN A 31491View Materials (Pacaud leg., Fig. 5View FIGURES 5 – 8. 5 a –c), 4 paratypes MNHN A 32900View Materials (Pacaud leg.) 5 paratypes MNHN A 31492View Materials (Faullummel coll.). All from type locality.

Stratum typicum. Early Eocene, Ypresian (Sparnacian), “Sands of Pourcy”.

Locus typicus. Pourcy, Marne, France. 49 ˚09ˏ 33 ˝ N 3 ˚ 54 ˏ 33 ˝ E.

Derivatio nominis. Named after Maurice Guilliou of Étoges, Marne, France, who has studied the fossils of the Paris Basin for many years and who first brought this taxon to the attention of the senior author.

Diagnosis. A rather small, globose Neritodryas  with 14 to 18 low, spiral ridges; septum edentate or with poorly defined teeth.

Description. Protoconch, worn in all known specimens, appears ovate, about 0.4 mm wide. Teleoconch consisting of about 2.5 whorls, globose with rather low but well-defined spire, large, rounded last whorl. Whorls convex, shouldered with short concavity immediately below impressed suture. On last whorl 14 to 18 low, flat or slightly rounded, spiral ridges with spaces between them approximately equal to width of ridges; ridges wider apart and broader at periphery. Fine, distinct, sinuous, collabral growth lines, opisthocyrt below suture. Aperture broad, septum smooth or with few slight curved ridges oblique to columellar edge; edge with slight, rounded swelling approximately one third of distance from adapical end, otherwise edentate or occasionally with up to 3 poorly defined teeth below it. Gutter between adapical end of the septum and outer lip. Outer lip thin, smooth within. Prominent ridge, slightly curved, below abapical end of septum. Holotype, though well preserved, without colour pattern, but yellowish grey colour apparent between ribs. Paratype illustrated in Figure 5View FIGURES 5 – 8. 5 has colour pattern of pale chevrons on dark brown background arranged in spiral lines, pointing in direction of growth.

Size. Holotype: height 15 mm, width 16 mm.

Remarks. Neritodryas guillioui  is very similar to Neritodryas globosa  (J. de C. Sowerby, 1823) ( Fig. 6View FIGURES 5 – 8. 5 a – c), assigned here to Neritodryas  rather than Nerita  , from the Bartonian of the Hampshire Basin, England, however Ns. globosa  has a larger number [ 25 in the neotype designated by Symonds (2002)] of more prominent and more closely spaced ribs than Ns. guillioui  . Symonds (2002) noted the similarity of Ns. globosa  to Neritodryas  but, with only the neotype available for study, did not move it to that genus. It is now clear, in view of the great similarity to Ns. guillioui  , that Ns. globosa  should be assigned to Neritodryas  . Neritodryas guillioui  is also very similar to Ns. dutemplei ( Deshayes, 1864)  ( Fig. 7View FIGURES 5 – 8. 5 a –c), again assigned here to Neritodryas  rather than Nerita  , which occurs with it in the Ypresian deposits at Pourcy. Neritodryas dutemplei  can be distinguished from Ns. guillioui  by the absence of conspicuous ribs in the former.

The operculum of Neritodryas  has longitudinal ribbing on one of the apophyses, which forms an important characteristic of this genus but, unfortunately, no operculum has yet been found for any of the three fossil species referred to above.

Range and distribution. Only known from type locality and one other site in the Ypresian (Sparnacian) at Pourcy, Marne, France.


Museum National d'Histoire Naturelle