Serpulidae, Rafinesque, 1815

Serpulidae View in CoL sp. 3

Fig. 13B View Fig .

Material.—Ten specimens attached to belemnite rostra from the middle Bathonian (Middle Jurassic) of Gnaszyn Dolny, Polish Jura (see Table 1); GIUS 8-3730.

Description.—Tubes medium-sized(ca. 20mm long), straight to slightly curved or slightly serpentine, nearly constant in diameter (up to 1 mm). The tubes with three very widely spaced keels; the two relatively weakly developed lateral keels located very close to the tube base. The prominent and thick median keel is occasionally slightly undulating. Small transverse ribs are most often well-visible, especially in the anterior tube part; they are densely and regularly spaced and curved forward, towards the three keels. Tubes most often attached to the substrate for their entire length with rare exceptions, where a part of the tube rises slightly above the substrate. The characteristic distribution of keels resulting in wide furrows in between them and thus triangular, subtriangular or otherwise angular cross-section.

Remarks.—Most of the tubes have been found on a single belemnite rostrum; they form a dense aggregation of closely spaced tubes. The specimens somewhat resemble species of several genera, but do not fully match any of those, so that we decided not to assign them to a definite genus. They resemble species of Propomatoceros and Placostegus in their triangular cross-section with a prominent median keel, and of Placostegus in the small and only slowly increasing tube diameter and small transverse ribs. However, they differ from these genera by possessing two lateral keels. Moreover, they slightly resemble Metavermilia ? sp. described above; however, their longitudinal ornamentation is less pronounced; the median keel forms a simple upper edge to the tube (“Kante” sensu Jäger 1983: 14, fig. 4a), and the lateral crests are only very delicate, placed at the very bottom lateral parts of the tubes.