Rhagasostoma operculatum, Koromyslova & Taylor & Martha & Riley, 2018

Koromyslova, Anna V., Taylor, Paul D., Martha, Silviu O. & Riley, Matthew, 2018, Rhagasostoma (Bryozoa) from the Late Cretaceous of Eurasia: taxonomic revision, stratigraphy and palaeobiogeography, European Journal of Taxonomy 490, pp. 1-66 : 28-31

Rhagasostoma operculatum sp. nov.

urn:lsid:zoobank.org:act:23F08F8D-29DB-4470-B8FA-B176256858F8

Fig. 11 , Table 6

Onychocella inelegans ( Lonsdale, 1850) – Favorskaya 1992: 125, pl. 64, fig. 7. — Favorskaya 1996: pl. 3, fig. 4. — Koromyslova 2014b: pl. 3, fig. 1.

non Onychocella inelegans – Favorskaya 1992: 125, pl. 64, fig. 6, pl. 65, fig. 1.

Diagnosis

Colony erect, bifoliate. Autozooids subrectangular, zooidal boundaries raised; gymnocyst lacking; cryptocyst extensive; opesia terminal, semielliptical; putative calcified opercula rounded trapezoidal. Avicularia interzooidal; rostrum channeled with rounded tip, between conical in outline and spade- shaped, asymmetrical; proximal part rounded, shorter and wider than rostrum; opesia egg-shaped with thin articular ridges bearing two short teeth proximally and a short opesiular indentation between the teeth; opesiules lacking.

Etymology

The species is named from the Latin ‘ operculum ’ because the opesiae of autozooids are presumably closed by calcified opercula.

Material studied

Holotype

TURKMENISTAN • Western Kopetdag, Kara-Kala ; boundary layers of the early Campanian ( Cibicidoides temirensis / Bolivinoides decoratus decoratus Zone ; LS 13) to middle Campanian ( Brotzenella monterelensis Zone ; LS 14) of the western Kopetdag ; TsNIGR Museum 27/12582 ( Fig. 11 A–C; figured by Favorskaya 1992: pl. 64, fig. 7).

Type locality and horizon

Turkmenistan, Western Kopetdag; boundary layers of the early to middle Campanian.

Description

Colony erect, flattened, bifoliate; fragments 6.0 mm long by 2 mm wide. Ancestrula and early astogeny not observed. Autozooids variable in shape, often broad and subrectangular with rounded distal ends; zooidal boundaries raised. Gymnocyst lacking. Cryptocyst extensive, finely pustulose, slightly depressed centrally, without peripheral caverns. Opesia terminal, semielliptical, presumably closed by calcified opercula. Putative opercula rounded trapezoidal and slightly concave, tubercular externally ( Fig. 11C ), proximal edge slightly arched and with ‘ears’ at the ends, which are 0.03–0.05 mm wide, ‘ears’ projecting 0.01–0.02 mm below the proximal edge. Septula not observed. Ovicells not observed. Avicularia interzooidal, longer than autozooids, elongate. Rostrum channeled with elevated walls and often rounded top, between conical in outline and spade-shaped, asymmetrical, dextral or sinistral. Proximal part rounded, shorter and wider than rostrum, cryptocyst pustulose, concave. Opesia eggshaped with the narrow end pointing upwards and with thin articular ridges bearing two short teeth proximally and short opesiular indentation between the teeth; opesiules lacking. Kenozooids, closure plates, intramural reparative budding autozooids, kenozooids, and avicularia not observed.

Remarks

Rhagasostoma operculatum sp. nov. differs from R. brydonei sp. nov., another species with a spadeshaped avicularian rostrum, in the rostrum having almost the same width along the whole of their length and having a pointed or rounded rostral tip instead of the rostrum being narrowed at the base, enlarged centrally and with a pointed tip. The new species differs from the other species described herein in having a spade-shaped avicularian rostrum instead of one that is conical in outline or falciform. Moreover, opesiae of autozooids of R. operculatum sp. nov. are presumably closed by calcified opercula.

Rhagasostoma operculatum sp. nov. is the earliest known species in cryptocystidean anascan cheilostomes that has putative calcified opercula. Late Cretaceous cheilostomes with calcified opercula from the family Onychocellidae include Inversaria flabellula (von Hagenow, 1846) from the late Campanian of Scania, Sweden,? Inversaria sp. from the late Campanian to Maastrichtian of United Arab Emirates, and Inversaria tubiporacea (Goldfuss, 1826) and Onychocella exilis Koromyslova & Shcherbinina, 2015 from the Maastrichtian of NW Europe and Uzbekistan, respectively ( Voigt & Williams 1973; Voigt 1974; Di Martino & Taylor 2013; Koromyslova 2014b; Koromyslova & Shcherbinina 2015). Calcified opercula have also been observed in several species belonging to the family Cribrilinidae Hincks, 1879 including Castanopora lambi Turner, 1975 from the Maastrichtian of USA ( Turner 1975; McKinney et al. 2003; Taylor & McKinney 2006).

Distribution

Early to middle Campanian Turkmenistan: western Kopetdag, Kara-Kala.

Figures

Fig. 11. Rhagasostoma operculatum sp. nov. A–C. Holotype, TsNIGR Museum 27/12582, western Kopetdag, Turkmenistan, boundary between the early and late Campanian (Cibicidoides temirensis/ Bolivinoides decoratus decoratus Zone, LS13). A. Overview of erect bifoliate colony. B. Autozooids with putative opercula and avicularia. C. Autozooids with putative opercula and avicularium. Scale bars: A = 1 mm; B = 500 µm; C = 200 µm.