Ostrovskia triforamina, Zágoršek & Gordon, 2013

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 : 604-606

Ostrovskia triforamina sp. nov.

Figs. 4 , 5 .

?1847 Eschara tubulifera Reuss, 1847: 67 , pl. 8: 19.

2010b Phoceana tubulifera ( Reuss, 1847) ; Zágoršek 2010b: 155, pl. 114: 1–5.

Etymology: Alluding to the three hollow apices of the triangular heterozooecium that lies against the proximal wall of the deep peristomial shaft. The frontal apex is the opening of the heterozooecium; the two basolateral apices connect with an areolar septular pore either side of the primary orifice.

Type material: Holotype: PM2 − T 1245 ( Fig. 4A ), sample BAS 4 . Paratypes: PM2 − T 1246 and T 1247 ( Figs. 4 , 5 ) , two specimens, samples BAS 4 .

Type locality: Başyayla section, Turkey .

Type horizon: Upper Tortonian , Miocene .

Referred material.— Eight specimens, five of which having ovicells ( PM2 − T 1134 , PM2 − T 1155 to PM2 − T 1158 ) .

Diagnosis.—As for the genus.

Description.—Colony erect, rigid, narrowly bilamellar with up to 10 longitudinal autozooecial series, circular to oval in cross section. Frontal shield evenly pseudoporous; marginal areolar pores of same diameter as pseudopores. Primary orifice at bottom of deep peristomial shaft; no sinus, the broad poster a little wide than the anter and one third its length, with a pair of condyles marking the boundary between them; proximal apertural rim straight or gently convex. Secondary orifice circular, surrounded entirely by broad, peristomial rim that is not markedly projecting, in the inner proximal margin of which is the tiny opening of a heterozooecium; chamber of heterozooecium triangular, with its apex at the peristomial rim and broadening as it descends so that at the level of the primary aperture it occupies the full internal width of the zooecium, its basolateral corners tubular, originating from an areolar septulum on each side. No frontal avicularia. Ovicell deeply concealed, opening into peristome above primary aperture; endooecium perforated by relatively large pores.

Measurements.—Given in µm, average value in brackets:

– width of colony branch: up to 1920

– width of autozooecium (external): 311–666 (469)

– length of autozooecium (external): 931–1380 (1029)

– width of autozooecium (internal): 284–407 (335)

– length of autozooecium (internal): 767–1160 (952)

– maximal width of heterozooecium (measured from internal side): 122–246 (171)

– minimal width of heterozooecium (measured from external side): 45–71 (57)

– diameter of orifice (external): 185–244 (215)

– diameter of orifice (internal): 156–318 (217)

– diameter of frontal pores (external): 20–37 (26)

– diameter of frontal pores (internal): 6–14 (9)

– diameter of peristome in section: 195–216 (208)

– width of ovicell (internal): 191–266 (232)

– diameter of ovicell pores (internal): 23–43 (29)

– diameter of areolar pores (measured from internal side): 18–27 (23)

– thickness of frontal wall in section: 208–356 (258)

Remarks.—In external view, our colonies show all of the features seen in the specimens attributed by Zágoršek (2010b) to Reuss’s (1847) species Eschara tubulifera , including the characteristic median convexity inside the apertures. Reuss’s (1847) type material differs, however, in having much longer peristomes and ovicells appear to be lacking. Study of the shield interior in the type material has not been possible owing to its type status and the Moravian material is too fragile because of its state of preservation. Accordingly, the attribution to E. tubulifera Reuss, 1847 is uncertain.

The intra−peristomial heteromorphic zooid is a striking feature, and the question arises as to its possible function. Its location suggests two possibilities—an avicularium, a glandular chamber, or both. The frontally visible apex of the heteromorph is a small intra−oral (not suboral) foramen. In this regard it is reminiscent of the suboral (sometimes intra−oral) avicularia that are seen in smittinids. These typically have a cross−bar, which has not been seen in our material of O. triforamina (the heteromorph appears damaged in our specimens). In smittinids, however, regardless of the position of the aperture of the suboral avicularium, its chamber is also suboral and rests upon the frontal shield. In Smittin a and Smittoidea it is median in position and originates from an areolar septular pore on either side. In Hemismittoidea it is slightly larger and off−centre and originates from a single marginal pore.

Waters (1894) was the first to document the occurrence of suboral glandular structures in a number of cheilostome species and Lutaud (1964) expanded on his list. She noted that Smittina landsborovii ( Smittinidae ) has probable glandular structures within the suboral avicularia. Taxa with larger suboral avicularian chambers (e.g., Hippadenella margaritifera , family incertae sedis) have more obvious such structures, and the glands can be as large as the avicularian adductor muscles. Given the relatively large internal volume of the heteromorph in Ostrovskia triforamina , it seems likely

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

that it could have been either a heteromorph with a solely glandular function or an avicularium with small musculature and larger glands. Carter et al. (2010) have demonstrated using TEM the dual function of some cheilostome avicularia.

Figures

Fig. 4. Exterior and interior view of an ascophoran bryozoan Ostrovskia triforamina gen. et sp. nov. from the Miocene of Turkey. A. PM2−T1245, holotype, exterior view showing arrangement of autozooecia and the broken tips of intra−peristomial heterozooecia visible on the proximal margin of the orifice, appearing as denticles. B. PM2−T1246, interior view showing immersed ovicell, marginal areolar−septular pore canals in section, perforation of frontal wall and small condyles on the sides of the orifice. C. PM2−T1247, detail of autozooecia showing ovicells with perforated endooecium and a small suboral area of imperforate frontal shield. D. PM2−T1134, detail of ovicell with entooecial perforations and, proximolateral to it on both sides, broken areolar−septular pore canals. All specimens from sample BAS 4. Scale bars A, 1 mm; B–D, 100 µm.

Fig. 5. Interior view of an ascophoran bryozoan Ostrovskia triforamina gen. et sp. nov. from the Miocene of Turkey. A. PM2−T1155, interior view of several zooecia showing a perforated ovicell, marginal areolar−septular pore canals in section, small pseudopores, and, in the left−hand zooecium, the interior of a triangular heterozooecium inside the peristome. B. PM2−T1157, proximal interior of a peristome with the fractured chamber of a triangular intraperistomial heterozooecium. C. PM2−T1158, detail of two broken peristomes showing triangular heterozooecium with small pores situated inside. D. PM2−T1156, oblique view of ovicell autozooecium showing perforation of ovicell and part of an intra−peristomial heterozooecium with one corner opening toward an interior areolar−septular pore. Scale bars 100 µm.