Pyrgopolon, DE MONTFORT, 1808

Kočí, Tomáš & Jäger, Manfred, 2015, Sabellid And Serpulid Worms (Polychaeta, Canalipalpata, Sabellida, Sabellidae, Serpulidae) From The Rocky Coast Facies (Late Cenomanian) At Předboj Near Prague, Acta Musei Nationalis Pragae Series B 71 (1 - 2), pp. 31-50 : 40

Pyrgopolon subgen. et sp. indet.

Pl. 2, Fig. 11–12

2012c Pyrgopolon (Septenaria) ? Pyrgopolon (Pyrgopolon) subsp. [sic!] indet. – Kočí, p. 126–127, fig. 1O–Q.

M a t e r i a l: Two large tubes.

S u b s t r a t e: The tubes had previously been attached to an unknown substrate.

D e s c r i p t i o n. Tube large, 5.5–7.4 mm wide (measured at the base) and 5.8–6.0 mm high at the aperture respectively at the anterior cross-section; length reaching more than 25 mm in the longest preserved fragment. Attached posterior portion slightly twisted to strongly curved, free anterior portion unknown if at all existing. The attached portion in some specimens bears three keels or rounded edges, in other specimens five, most of them are inconspicuous except for the very broad flat median keel which shows a distinct chevron-like or V-like pattern of strongly protruding incremental lines. Cross-section rounded triangular posteriorly but tunnel-shaped or rounded trapezoid anteriorly. Lumen circular. Tube wall thick, with a thin innermost tube layer which is slightly separated from the main tube layer.

R e m a r k s a n d r e l a t i o n s h i p s. In the Late Cretaceous of Europe the vast majority of Pyrgopolon specimens belong to one of two subgenera, P. ( Pyrgopolon ) and P. (Septenaria), which may look more or less similar in outer aspect but are usually well distinguishable by several features of the tube structure: usually P. ( Pyrgopolon ) has a moderate to thin tube wall and well-developed chambered tubulae in the lateral areas of the attached tube base, and often its inner tube layer is more or less separated from the outer tube layer during diagenesis. In contrast, P. (Septenaria) has a moderate to thick tube wall, which in the lower half of the attached portion may show “ Favosites structure” which is a cellular structure resembling that of the Paleozoic coral genus, and some specimens may show a honeycomb-like ornamentation on the surface of the tube.

The problem with the present species is that it combines features of both previously mentioned subgenera, and plus the low number of available specimens mean it is therefore impossible to affiliate it to any subgenus at the present state of knowledge. Features pointing to P. ( Pyrgopolon ) are a thin innermost tube layer which is slightly separated from the main tube layer and the nondevelopment of a “ Favosites structure” ( Jäger 1983, Jäger and Breton 2002) and honeycomb-like ornamentation. Features pointing to P. (Septenaria) are the thick tube wall and the absence of tubulae.

In its relatively large size and thick tube wall, the present species resembles Pyrgopolon (Septenaria) sp. B ( Kočí 2010) which, however, has a thicker external tube layer and developed cellular layers.