Oncousoecia sp.

Hara, Urszula & Taylor, Paul D., 2009, Cyclostome bryozoans from the Kimmeridgian (Upper Jurassic) of Poland, Geodiversitas 31 (3), pp. 555-575 : 563

Oncousoecia sp. ( Fig. 5 )

MATERIAL EXAMINED. — Małogoszcz Quarry: NHM BZ 5519(1). — Wierzbica Quarry: NHM BZ 5513, BZ 5514.

MEASUREMENTS. —Width of branches = 0.4-1.2 mm; longitudinalaperturaldiameter = 0.05-0.07 mm; trans-

verse apertural diameter = 0.04-0.06 mm; longitudinal peristomediameter = 0.08-0.11 mm; transverseperistome diameter = 0.06-0.08 mm; frontal wall length = 0.22- 0.35 mm; frontal wall width = 0.09-0.12 mm; gonozooid length = 0.40 mm; gonozooid width = 0.40 mm; ooeciopore length = 0.04 mm; ooeciopore width = 0.08 mm.

OCCURRENCE. — Lower Kimmeridgian, Wierzbica and Małogoszcz quarries, Holy Cross Mts, Poland.

DESCRIPTION

Colony encrusting, with ribbon-like, oligoserial branches, usually between three and eight zooids wide, forming lobate expansions, relatively flat, seldom bifurcating ( Fig. 5B ), occasionally anastomosing, uniserial in early astogeny.

Autozooids very small, rather short, visible throughout their lengths, with transversely wrinkled frontal walls. Apertures nearly subcircular or slightly transversely elliptical, bordered by a narrow peristome tapering distally. Pseudopores drop-shaped, about 10 µm wide.

Gonozooids low in profile, as wide as long, more or less inverted pear-shaped, bulbous in the distal part. Ooecioporesubterminal, transversely elongate.

REMARKS

Specimens of Oncousoecia described from the Lower Kimmeridgian of Poland occur as small and delicate encrusting colonies with ribbon-like oligoserial branches ( Fig. 5 A-C). Transverse and longitudinal apertural measurements and frontal wall length and width, as well as the morphology of the frontal wall, are almost the same as in Oncousoecia parvula (Canu & Bassler, 1926) , as redescribed by Pitt & Taylor (1990) from the Aptian Faringdon Sponge Gravel. Th e main difference lies in the morphology of the gonozooid which in the Polish Lower Kimmeridgian material is triangular or inverted pear-shaped, as well as the ooeciopore which is subterminal ( Fig. 5F ) rather than terminal.

Oncousoecia elengatula (d’Orbigny, 1850) , ranging from Upper Aalenian to Upper Bajocian according to Walter (1970: 25), has a similar frontal wall width to the Polish Kimmeridgian specimens, and thisfeature is one of the more usefulmorphometric characters for distinguishing Jurassic cyclostome species. Th e sole species of Oncousoecia sp. from the Middle Upper Oxfordian of Baltow (Holy Cross Mts, Poland) (see Hara & Taylor 1996) is somewhat similar to the Lower Kimmeridgian species. However, the width of the frontal wall in the Lower Kimmeridgian material is smaller and the gonozooid has a different shape, being inverted pear-shaped rather than pyriform as in the Baltow specimen. In view of the sparse and indifferently preserved material available from the Polish Lower Kimmeridgian, species determination is deferred.

Figures

FIG. 5. — Oncousoecia sp.,Lower Kimmeridgian,Holy Cross Mts,Poland:A-E, NHM BZ 5519(1),Małogoszcz Quarry;A, lobate branches; B, oligoserial branch; C, branches growing over shell substrate grazed by echinoids; D, autozooids; E, autozooidal pseudopores; F, NHM BZ 5513, Wierzbica Quarry, gonozooid with ooeciopore arrowed. Scale bars: A-C, 1 mm; D, F, 200 μm; E, 100 μm.