Placostegus rigidus ( REGENHARDT , 1961)

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 : 37

Placostegus rigidus ( REGENHARDT, 1961)

Pl. 1, Fig. 9, 10; Pl. 3, Fig. 4

1961 Eoplacostegus (Eoplacostegus) rigidus n. sp. – Regenhardt, p. 61, pl. 5, fig. 4.

1983 Eoplacostegus rigidus REGENHARDT, 1961 – Jäger, p. 98–99, pl. 12, fig. 1–3.

2005 Placosteugs rigidus ( REGENHARDT, 1961) – Jäger, p. 170.

2012b Placostegus sp. – Kočí, p. 123, fig. 1I–K.

M a t e r i a l: Six specimens in which at least parts of the attached posterior tube portion as well as the free rising anterior tube portion are preserved, one coil, and 21 specimens of which only the free anterior tube portion is preserved.

S u b s t r a t e: One specimen is attached to an oyster valve Ostrea sp. , another specimen is attached to a bryozoan stem. Vice versa, three Placostegus tubes are used as substrates, each of them by a Dorsoserpula bipartita tube.

D e s c r i p t i o n. The posterior tube portion attached to the substrate is straight or coiled to form a loop, the anterior free tube portion is long and rises steeply. One sharp, sometimes undulating keel is present in the posterior tube portion, three sharp keels in the free tube portion, forming three spines surrounding the aperture of the free tube portion. Between the keels a narrow longitudinal furrow may be present. Apart from the keels and furrows, the surface of the tube appears to be smooth at first sight, but under the microscope very fine distinct transverse corrugations are visible. Cross-section of the tube triangular, subtriangular or, less typical, square.

R e m a r k s a n d r e l a t i o n s h i p s. The tube of Placostegus velimensis JÄGER et KOČÍ, 2007 is similar in shape, but the present species has a narrower tube diameter, less developed transverse ornamentation, and most tubes are triangular to subtriangular instead of square in cross-section. The tube of Placostegus aduncus ( REGENHARDT, 1961) is similar, too, but it differs by its often very well developed transverse ribs. Also Placostegus zbyslavus differs from the present species by its transverse ornamentation and its possibly more often planispirally coiled attached posterior tube portion.