Ostrovskia

Zágoršek, Kamil & Gordon, Dennis P., 2013, Late Tortonian bryozoans from Mut Basin, Central Anatolian Plateau, southern Turkey, Acta Palaeontologica Polonica 58 (3), pp. 595-607 : 602-604

Genus Ostrovskia nov.

Type species: Ostrovskia triforamina sp. nov., see below.

Etymology: For Dr Andrei N. Ostrovsky, in recognition of his illuminating studies on cheilostome reproductive structures.

Diagnosis.—Colony erect, rigid, narrowly bilamellar, branches circular to oval in cross section. Frontal shield evenly pseudoporous with indistinguishable areolar pores. Primary orifice concealed within peristomial shaft; anter semicircular, poster a little wider, small condyles, proximal rim straight or gently convex, no sinus. Peristomial (secondary) orifice circular, surrounded entirely by broad rim, in the inner proximal margin of which is tiny opening of heterozooecium that originates internally from a pair of areolar septula. No frontal avicularia. Ovicell concealed, opening into peristome above primary orifice; entooecium perforated by relatively large pores.

Remarks.—The family and even the superfamily are uncertain. The most distinctive feature of the genus is a triangular heterozooecium that lies against the proximal wall of the deep peristomial shaft. The apex of the heterozooecium is a tiny opening that, in the best−preserved specimens, appears as a small circular foramen, but it is often damaged and, in frontal view, the broken edge can appear as a denticulate structure. Internally, the chamber of the heterozooecium broadens to form a flattened triangular shape, with its tubular proximal corners originating from a pair of areolar septular pores. In this regard, the topology of the structure is reminiscent of the median suboral or intraoral avicularium of a smittinid; however, the ovicell is deeply concealed by cryptocystal secondary calcification, which is atypical of smittinids.

As Zágoršek (2010b: 155) has remarked when describing this species as Phoceana tubulifera ( Reuss, 1847) , the type species of Ostrovskia resembles Smittina cervicornis ( Pallas, 1766) in general appearance, but only when the peristome is not produced. In specimens in which a peristome is present, a general similarity to Phoceana Jullien in Jullien and Calvet, 1903 has led to previous inclusion in that genus, beginning with David and Pouyet (1974). It is doubtful if this connection is valid, however. In the type species of Phoceana , P. columnaris Jullien , in Jullien and Calvet, 1903, the frontal shield is non−pseudoporous. Very little is known about P. columnaris , however, and neither avicularia nor ovicells

http://dx.doi.org/10.4202/app.2011.0100

were described. Phoceana acadiana Lagaaij, 1963 , however, appears to be conspecific with P. columnaris ( Lagaaij [1963] was able to examine a specimen of P. columnaris from the Mediterranean) and it has a primarily non−pseudoporous frontal shield “with irregular patches of white tremocyst”; this description suggests that the frontal pores in this species may be derived from lateral areolar pores in secondary calcification. It also has ovicells “lodged in the acute angle between the peristome and the outer wall of the zoarial branch” but Lagaaij (1963) did not illustrate these. Largely on the basis of the frontal shield, we conclude that P. tubulifera does not belong to Phoceana .

One of the specimens illustrated by Zágoršek (2010b: pl. 114: 1) has an ovicell. This is in a zooecium near the distal end of a neanic branch in which secondary calcification is not so thick. Hence it is likely that newly formed zooids have a relatively long peristome and ovicells are still visible as a bulge in the wall, but, as secondary calcification increases, it rises to the level of the peristomial opening and the ovicells becomes deeply concealed. The neanic ovicell is nevertheless covered by a cryptocystal layer that resembles the pseudoporous frontal shield, hence it is “schizoporelloid” rather than “smittinoid”. For this reason, assigning Ostrovskia to a particular family is difficult. Overall, we conclude that the superfamily is Schizoporelloidea sensu lato, but cannot suggest a family.