Plagioecia rugosa (d’Orbigny, 1853)

Hara, Urszula & Taylor, Paul D., 2009, Cyclostome bryozoans from the Kimmeridgian (Upper Jurassic) of Poland, Geodiversitas 31 (3), pp. 555-575 : 569

? Plagioecia rugosa (d’Orbigny, 1853) ( Fig. 9 )

Berenicea rugosa d’Orbigny, 1853: 861 .

Plagioecia rugosa – Hara & Taylor 1996: 97, figs 21, 22.

MATERIAL. — Deltoideum Beds, Wierzbica Quarry : NHM BZ 5512(2). — Małogoszcz Quarry: NHM BZ 5524, BZ 5525.

MEASUREMENTS. — Longitudinalaperturaldiameter = 0.09-0.12 mm; transverseaperturaldiameter = 0.08- 0.11 mm; frontal wall length = 0.51-0.66 mm; frontal wall width = 0.15-0.18 mm.

OCCURRENCE. — Lower Kimmeridgian, Wierzbica and Małogoszcz quarries, Holy Cross Mts, Poland. Originally described from the Kimmeridgian of Angoulins, France (d’Orbigny, 1853).

DESCRIPTION

Colony multiserial, unilamellar or multilamellar, moderately thick, circular to subcircular in outline, occasionally developing marginal or frontal subcolonies that overgrow the parent colony. Growing edge exposing several generations of zooidal buds with stout mural tubercles covering surfaces of interior walls. Colony surface crossed by prominent transverse ridges, semi-regularly spaced (0.06-0.08 mm apart), low in profile and occasionally indistinct, curved in direction of colony growth.

Autozooids immersed proximally, slightly convex distally, moderately large. Apertures relatively small, closely-spaced, arranged in quincunx, slightly longitudinally elongate; preserved peristomes low, thick. Terminal diaphragms present, frequent. Pseudopores roughly circular in shape.

Gonozooids not observed in the Polish Lower Kimmeridgian material.

REMARKS

Three bereniciform colonies among the material studied are notable for havingsurfaces ornamented bytransverse ridges.Th isfeature characterises several species from the Jurassic (see Hara & Taylor 1996), includingtwo that inviteparticular comparison with the Polish Lower Kimmeridgian material: Hyporosopora baltovensis Hara & Taylor, 1996 fromthe Middle Upper Oxfordian of Baltow in Poland, and Plagioecia rugosa from the Lower Kimmeridgian of Charente-Maritime in France. Whereas the gonozooid in H. baltovensis is rounded subtriangular and lacks penetrating autozooids ( Hara & Taylor 1996: fig. 11), that of P. rugosa is broader and has a few autozooids piercing the roof ( Hara & Taylor 1996: fig. 22). Autozooid size is very similar in the two species but the transverse ridges appear to be more prominent in P. rugosa than in H. baltovensis . Unfortunately, available material from the Polish Lower Kimmeridgian (Wierzbica and Małogoszcz quarries) is infertile, making its identification difficult. Nevertheless, we favourtentative assignment to P.rugosa because of thewell-developed transverse ridges, especially in a colony from Małogoszcz Quarry ( Fig. 9E ), andalso the presence of marginal subcolonies ( Fig. 9A ). Th e latterhave beenobserved in material of P. rugosa (e.g., NHM BZ3105) from the type region near La Rochelle but have not been seen in H. baltovensis .

Figures

FIG. 9. –?Plagioecia rugosa (d’Orbigny,1853), Lower Kimmeridgian,Holy Cross Mts, Poland: A-C, NHM BZ5512(2), Deltoideum beds, Wierzbica Quarry; A, edge of colony with damaged marginal subcolony (top); B, frontal subcolony; C, autozooids and transverse ridges; D-F, NHM BZ 5524, Małogoszcz Quarry; D, worn colony edge; E, detail of autozooidal apertures and broad, flat-topped transverse ridges; F, new buds at abraded growing edge showing prominent mural tubercles. Scale bars: A, 1 mm; B-D, 500 μm; E, 200 μm; F, 100 μm.