Pyrgopolon (Turbinia?) gaiae 1808

Sanfilippo, Rossana, Rosso, Antonietta, Reitano, Agatino & Insacco, Gianni, 2017, First record of sabellid and serpulid polychaetes from the Permian of Sicily, Acta Palaeontologica Polonica 62 (1), pp. 25-38 : 32-33

Pyrgopolon (Turbinia?) gaiae sp. nov.

Fig. 7 .

Etymology: Named after Gaia, the daughter of RS.

Holotype: One opercular cup ( MSNC4530 ), with exposed upper surface, the remaining parts hidden by embedding lithified calcilutite.

Type locality: Sosio Valley, western Sicily ( Italy).

Type horizon: “Pietra di Salomone” Limestone, Wordian to upper Permian.

Diagnosis.—Cup conical, upper side concave with numerous (34), straight radial ridges. Radial ridges relatively low, inversely U-shaped in cross-section, not reaching the centre of the cup. Outer margin of the cup forming a characteristic thick band, sculptured by numerous, regularly spaced teeth that give it the aspect of a cogwheel.

Description.—The cup is conical, 2.3 mm in diameter. The upper side is sculptured by 34 relatively low and straight radial ridges, occupying about 3/4 of the cup radius, around a smooth central depression. They are of similar length, a few ones being shorter, starting from about mid length. Ridges are inversely U-shaped in cross-section becoming thicker and more prominent towards the edge. Edge of the cup thick, sculptured like a cogwheel, with regularly spaced (0.15 mm) conical teeth each corresponding to a ridge’s termination, forming a nearly continuous ring with their bases.

Remarks.—Serpulid opercula are modified radioles of the branchial crown very variable in shape and structure, thus extensively used as taxonomic characters, both at generic and specific level. Only some serpulids possess a calcified operculum, the mineralization being normally restricted to the terminal plate. In other serpulids the terminal plate remains chitinous. In a few genera, as in Pyrgopolon , the operculum is entirely calcareous ( Hove 1973; Hove and Nishi 1996; Vinn and ten Hove 2011) and thus its fossil record is diagnostically important for systematics of fossil serpulids.

The operculum described as P. (T.) gaiae has been found disconnected from its tube. It has a diameter larger than the lumina of any serpulid known from the investigated association. Nevertheless, the concave upper side of the cup and the strait radial ridges are typical of the opercula known for species of the genus Pyrgopolon de Montfort, 1808 and are sufficient to establish a separate species. In addition, the thick denticulate band on the margin of the cup and the inversely U-shaped radial ridges allow to include the new operculum in Turbinia Michelin, 1845 which Jäger (1993) considers to be a subgenus of Pyrgopolon . Particularly, the new species is similar to P. ( Turbinia ?) cunialense Gatto and Radwańska, 2000, but differs for its larger size (diameter 2.3 mm instead of 0.7–1.36 mm), more concave shape and the lower number of radial ridges (34 instead of 36–46) ( Gatto and Radwańska 2000: 350–351, pls. 7, 8).

The strong similarity between the new Permian species and those described by Gatto and Radwańska (2000) from the upper Eocene on NE Italy, was unexpected and points to a certain persistence of such morphological features during very long geological time. Furthermore, the new species P. (T.) gaiae largely predates the first appearance of Pyrgopolon , hitherto known from the Barremian, Early Cretaceous ( Jäger 2011). This finding thus highlights a wide geographic and temporal hiatus with previous known occurrences.

Stratigraphic and geographic range.—Wordian to upper Permian of Italy.

Figures

Fig. 7. Operculum of serpulid Pyrgopolon (Turbinia?) gaiae sp. nov. from the Sosio Valley, western Sicily (Italy), Wordian to upper Permian, MSNC 4530, holotype. Frontal (A) and lateral (B) views of the cup. C. Detail of upper side of the cup showing radial ridges endings with cone-shaped teeth regularly spaced (0.15 mm). D. SEM image of the upper side of the cup, the denticulated outer edge forming a nearly continuous ring is obvious.