Idmonea sp.

Zatoń, Michał & Taylor, Paul D., 2009, Middle Jurassic cyclostome bryozoans from the Polish Jura, Acta Palaeontologica Polonica 54 (2), pp. 267-288 : 280-281

Idmonea sp.

Fig. 10 .

Material.—GIUS 8−3509−19, Gnaszyn Dolny, Middle Bathonian, comprising six branch fragments, partially coated by siderite, retrieved from a sample interpreted as a regurgitate by Zatoń and Salamon (2008).

Measurements.—FWL, 400–507 µm; FWW, 147–187µm; LAM, 80–107 µm; TAM, 67–107 µm; LPM, 120–133 µm; TPM, 93–133 µm; PW, 8 µm.

Description.—Colony erect comprising bifurcating branches about 820 µm in diameter, ovoidal in cross−section.

Autozooid frontal walls flat to slightly convex, a distinct convex boundary wall present. Apertures transversely elliptical or circular, some closed by terminal diaphragms, variable in size with those located at the midline of the branches being largest ( Fig. 10A ). Peristomes short, upright. Pseudopores small and dense, teardrop−shaped, about as long as wide, pointed distally ( Fig. 10B ).

Gonozooids not observed.

Remarks.—Historically, the tubuliporine genus Idmonea has been interpreted in different ways, either as an encruster with branches of a subtriangular shape in cross−section, or as an erect genus with branches of similar cross−sectional shape. As was noted by Pitt and Taylor (1990), the Jurassic type species, I. triquetra Lamouroux, 1821 , has encrusting branches. However, from the encrusting base, erect branches may arise with ovoidal cross−sections and autozooids opening around the entire circumference ( Walter 1970). These contrast with branches of erect species historically assigned to Idmonea , signifying a taxonomic difference. The erect branches described here from the Polish Jurassic do, however, possess an ovoidal cross−section, although the morphology of the encrusting base is unknown. The branches were found in the sample interpreted as regurgitate by Zatoń and Salamon (2008). Therefore, they may have been swallowed by a durophagous marine vertebrate, either incidentally or as part of its normal diet.

Stratigraphic and geographic range.—Middle Bathonian of Gnaszyn Dolny, Polish Jura.

Figures

Fig. 10. Multisparsid cyclostome bryozoan Idmonea sp. from the Middle Jurassic ore−bearing clays of the Polish Jura, GIUS 8−3509−19. A. Autozooids. B. Pseudopores.Middle Bathonian (Morrisiceras morrisi Zone), Gnaszyn Dolny.Scale bars: 200 µm (A), 20 µm (B). BSE SEM images of uncoated specimens.