Danilia pterostomus (Bronn, 1861)

Sacchetti, Claudia, Landau, Bernard & Ávila, Sérgio P., 2023, The Lower Pliocene marine gastropods of Santa Maria Island, Azores: Taxonomy and palaeobiogeographic implications, Zootaxa 5295 (1), pp. 1-150 : 23-24

Danilia pterostomus (Bronn, 1861)

Fig. 1 A

* Trochus pterostomus Bronn in Hartung 1861: 119, pl. 19, fig. 2.

Trochus pterostomus Br. in Hartg.—Bronn in Reiss 1862: 32.

Craspedotus pterostomus Bronn — Mayer 1864: 62, pl. 6, fig. 40 (43 in text, lapsus).

Type material. Single specimen height 5.0 mm, width 4.0 mm, Forno do Cré, Santa Maria Island , Azores; whereabouts unknown ( Beu 2017: 165) .

Original description. “ Eine ganze Schale, doch mit der Hinterseite fest im Gesteine sitzend, und die Nabelgegend undeutlich. Sie ist flach-kugelig, kaum 5 Mm. hoch und etwas breiter (a), mit 3–4 rund-geŵlbten Umgängen und scharf eingedŗckter Naht. Gr̂sse und Habitus sind wie bei den kleinen Clanculus -Arten ( Trochus Couturi, Tr. Vieilloti Payr. ), und wie bei diesen ist die ganze Oberfläche des letzten Umgangs (c, d) mit 13–14 dicht gedrängten runden gekerbten Spiral Reifen und fein querstreifigen Zwischenfurchen versehen, wodurch dieselbe ein sehr fein gegittertes Ansehen erhält. Der vorletzte fast halb-cylindrische Umgang zeigt noch etwa 6—7 derselben auf seiner freien Oberfläche. Was inzwischen diese Art besonders auszeichnet, das ist ein sehr ḑnner blattartiger radial nach aussen umgeschlagener Saum des rundlichen Mundes, wie bei den meisten Cyclostoma -Arten. Ueber die Beschaffenheit des Nabels und die Anwesenheit von Zähnen auf dem inner-unteren Mundrande war keine Gewissheit zu erlangen; doch scheint es, als ob diese fehlten und hinter dem Mundsaume nur ein Nabelspalt herabẑge. Die runde M̧ndung entspricht zwar der Sippe Turbo besser als Trochus ; aber ich rechne zu Turbo nur Arten mit kalkigem Deckel. [Shell complete, dorsal side covered with matrix, umbilical area indistinct. Flat-spherical, about 5mm in height and a little wider (a), with 3-4 rounded whorls separated by deep suture. Size and shape are like the small Clanculus species ( Trochus Couturi, Tr. Vieilloti Payr. ), and as with these, the surface of the last whorl (c, d) is covered by 13-14 narrow, rounded densely notched spiral cords crossed by fine axial growth lines, giving finely reticulated appearance. The penultimate, almost half cylindrical whorl bears still about 6-7 of the same on its free surface. What distinguishes this species in particular is a very thin leaf-like rounded apertural rim turned radially outwards, as in most Cyclostoma species. Nothing certain can be said about the nature of the umbilicus and the presence or absence of teeth on the inner-lower apertural margin; but it seems as if these were missing and behind the rim of the mouth only an umbilical fissure. The round mouth corresponds to the Turbo group better than Trochus ; but I only count species with a calcareous operculum as Turbo.]” (Bronn in Hartung 1861: 119).

Latin description. “ Testa parva , conoidea, imperforata ; anfractibus 5, convexis, sutura canaliculata separatis, cingulis elevatis sex, in ultimo autem decem, lineisque elevatis obliquis, aequidistantibus elegantissime clathratis; apertura fere orbiculari; labro intus sulcato, extus varice crasso, supra quem cingula excurrunt, marginato; labio fovea et dente basali instructo ” ( Mayer 1864: 62).

Discussion. We agree with Mayer (1864) who placed this species in the genus Craspedotus Philippi, 1847 which is considered a synonym of Danilia Brusinia, 1865 ( Craspedotus Philippi, 1847 is a junior homonym of Craspedotus Schoenherr, 1844 [ Coleoptera ]). No further specimens are available from Santa Maria Island. The teleoconch sculpture is closely similar to that of D. otaviana ( Cantraine, 1835) from the Pliocene and Pleistocene Mediterranean (see Landau et al. 2003: pl. 17, fig. 2), but differs in being far smaller. The first two whorls of Danilia pterostomus (Bronn, 1861) seems to be unsculptured. In the absence of further material or an illustration of the apertural side, it is difficult to comment further. We note some confusion in the descriptions, as the original description said the “ Hinterseite ” [back side] is stuck fast to the matrix. The back side is usually the dorsum which was illustrated by Bronn in Hartung (1861: pl. 19, fig. 3). If it is the venter that is obscured by matrix, it is strange that Mayer gave a description of the aperture, unless Bronn or Mayer removed the matrix sometime after the original description.

Distribution. Lower Pliocene: Atlantic, Santa Maria Island, Azores (Bronn in Hartung 1861; Bronn in Reiss 1862; Mayer 1864).

Figures

FIGURE 1. Location map of the Azores Archipelago with information about the bathymetry and regional tectonic settings. NA—North American plate; EU—Eurasian plate; Nu—Nubian (African) plate; MAR—Mid‐Atlantic Ridge; TR—Terceira Rift; EAFZ—East Azores Fracture Zone; GF—Gloria Fault (adapted from Hyžný et al. 2021).