Rhagasostoma gibbosum
Creators: name: Koromyslova, Anna V.
name: Taylor, Paul D.
name: Martha, Silviu O.
name: Riley, Matthew
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Bryozoa
Gymnolaemata
Cheilostomatida
Onychocellidae
Rhagasostoma
Rhagasostoma gibbosum

description: Rhagasostoma gibbosum (Marsson, 1887)
Figs 12–13, Table 7
Eschara gibbosa Marsson, 1887: 71, pl. 7, fig. 2.
Rhagasostoma subgibbosum Brydone, 1930: 48, pl. 26, fig. 11. Syn. nov.
Rhagasostoma gibbosum var. weybournensis Brydone, 1930 pars: 48, pl. 26, figs 13–14. Syn. nov.
Rhagasostoma gibbosum –? Levinsen 1925: 369. — Brydone 1930: pl. 26, fig. 15.
Onychocella gibbosa –? Voigt 1930: 460, pl. l8, fig. 15. —? Veenstra 1963: 107, pl. fig. 5.
non Rhagasostoma gibbosum var. weybournensis – Brydone 1930 pars: 48, pl. 26, fig. 12.
Material studied
Figured material
GERMANY • 2 specs; Schleswig-Holstein, Saturn quarry near Kronsmoor; early Maastrichtian; SMF 29906 (Fig. 12 A–E), 29907 (Fig. 12F).
UNITED KINGDOM • England, Norfolk; early Maastrichtian (Ostrea lunata Zone) of Trimingham; SM B36679 (Fig. 12G; figured by Brydone 1930: pl. 26, fig. 15).
BELARUS • 3 specs; Grodno Region; erratic block of?late Campanian age in a quarry near Hrodna / Grodno (Гродна/ Гродно); PIN 2922 /216 (Fig. 13B), 2922/218 (Fig. 13A), 2922/275 (Fig. 13C).
KAZAKHSTAN • 2 specs; Emba River; late Campanian (Belemnitella lanceolata Zone); PIN 5502/3058 (Fig. 13D), 5502/3059 (Fig. 13E).
Other material
BELARUS • Grodno Region; erratic block of?late Campanian age in a quarry near Hrodna / Grodno (Гродна/ Гродно); PIN 2922 /274.
Description
Colony erect, with flattened bifoliate branches (3–4 mm wide).Ancestrula and early astogeny not observed. Autozooids variable in shape, often broad and subrectangular with rounded distal ends; zooidal boundaries raised. Gymnocyst sometimes observed (Figs 12G, 13E). Cryptocyst extensive, finely pustulose, slightly depressed or slightly convex centrally, sometimes with proximal peripheral caverns (Fig. 13B, C). Opesia terminal, rarely subterminal, semielliptical with distal shelf, a thin inner wall delimiting the distolateral part of the opesia and a thickened, projecting outer wall delimiting the proximolateral part (Figs 12C, 13C). Proximal edge of opesia straight, smooth, thickened, with proximolateral outgrowths defining small opesiules at the corners; outgrowths often destroyed, giving opesiules the appearance of opesiular indentations. Septula not observed. Ovicells endozooidal, ooecium is formed by the distal zooid, wellrecognizable, with cryptocyst-like surface and arch-like proximal edge with elongated proximolateral processes extending along the cryptocyst of the maternal zooid (Figs 12B, D, G, 13B, D–E). Avicularia interzooidal, smaller than autozooids, elongate. Rostrum channeled, symmetrical, with elevated winglike walls and a pointed tip, rising above the surface of the colony and tilted to the right or left, rostral tip not reaching the opesia of the distal autozooid. Rostrum tilted over the proximal part of the distal autozooid or the ooecium of a maternal autozooid. Wedge-like structures present (Fig. 12 B–D), extending from the base to the middle of the rostrum and partially covering the opesia, but often these structures are broken (Fig. 12E). Proximal part rounded, shorter and wider than rostrum, cryptocyst pustulose, concave, without peripheral caverns. Opesia roundish, with two short teeth proximally, opesiules lacking (Fig. 12E). Kenozooids subcircular, located along the branch margins (Fig. 12A). Cryptocyst finely pustulose, opesia roundish (Figs 12C, 13A, D–E). Intramural reparative kenozooidal buds sometimes observed within host autozooids and avicularia (Fig. 13 D–E), all with the same polarity as the host zooid. Closure plates, intramural reparative budding autozooids and avicularia not observed.
Remarks
The type material of Rhagasostoma gibbosum (Marsson, 1887) could not be found, although part of the Marsson Collection has recently been recovered (Martha 2014). From the similar species R. tchvanovi (Favorskaya, 1992), R. gibbosum differs in having a rostrum that is short and tilted to the right or left instead of being long and almost straight. Rhagasostoma gibbosum can be distinguished from R. gibbosulum by the slightly convex border of the cryptocyst and the very rare presence of a gymnocystal portion.
Distribution
Late Campanian Belarus: Quarry near Hrodna / Grodno (Гродна/ Гродно), Grodno Region. Kazakhstan: Emba River. Early Maastrichtian United Kingdom: Trimingham, Norfolk, England. Germany: Saturn quarry near Kronsmoor, Schleswig-Holstein, Island of Rügen, Mecklenburg-Vorpommern.Maastrichtian: unspecified localities in Denmark.
description: Published as part of 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, pp. 1-66 in European Journal of Taxonomy 490 on pages 31-35, DOI: 10.5852/ejt.2018.490, http://zenodo.org/record/3830845