Rhagasostoma gibbosulum Brydone 1936
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 gibbosulum

description: Rhagasostoma gibbosulum Brydone, 1936
Fig. 14, Table 8
Rhagasostoma gibbosulum Brydone, 1936: 74, pl. 36, fig. 1.
Material studied
Holotype
UNITED KINGDOM • England, High Down; middle Campanian (Belemnitella mucronata Zone) of Isle of Wight; SM B36887 (Fig. 14 A–D; figured by Brydone 1936: pl. 36, fig. 1).
Additional figured material
BELARUS • Grodno Region; erratic block of?late Campanian age in a quarry near Hrodna / Grodno (Гродна/ Гродно); PIN 2922 /242 (Fig. 14 E–F).
GERMANY • 4 specs; Schleswig-Holstein, Saturn quarry near Kronsmoor; early Maastrichtian; SMF 29908 (Fig. 14 G), 29909 (Fig. 14 H), 29911 (Fig. 14 I), 29912 (Fig. 14 J).
Other material
GERMANY • 2 specs; same data as for preceding; SMF 29910, 29913.
Description
Colony erect, with flattened bifoliate branches (1–6 mm wide). Ancestrula and early astogeny not observed.Autozooids variable in shape, often broad and roundish; zooidal boundaries raised.Gymnocyst? present proximolaterally, smooth (Fig. 14B, G, I), but usually not visible. Cryptocyst extensive, finely pustulose, usually slightly convex centrally. Opesia terminal or subterminal, semielliptical, delineated by two walls, a thin inner wall forming the distolateral rim and a projecting and thickened outer wall forming the proximolateral rim. Proximal edge of opesia straight, smooth, with outgrowths at the two proximolateral corners delineating small opesiules; outgrowths often destroyed, giving the opesiules the appearance of opesiular indentations (Fig. 14C, I–J). Septula not observed. Ovicells endozooidal, ooecium is formed by the distal zooid, well-recognizable, with cryptocyst-like surface and arch-like proximal edge with elongated proximolateral processes extending along the cryptocyst of the maternal zooid (Fig. 14I). Avicularia interzooidal, smaller than autozooids, elongate. Rostrum channeled, asymmetrical, rarely symmetrical, with elevated wing-like 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 distal autozooid. Rostrum tilted over gymnocyst of the distal autozooid or ooecium. Wedge-like structures present (Fig. 14 I–J), extending from the base to the middle of the rostrum and partially covering the opesia, but often these structures are broken (Fig. 14D). Proximal part of avicularium rounded, shorter and wider than rostrum, cryptocyst pustulose, concave, but often not visible. Opesia round with two short teeth proximally, opesiules lacking (Fig. 14J). Kenozooids sometimes numerous, located along edges of branches, roundish (Fig. 14H). Cryptocyst finely pustulose. Opesia round. Intramural reparative kenozooidal buds in host autozooids sometimes observed (Fig. 14B), all with the same polarity as the host zooid. Closure plates and intramural reparative budding of autozooids and avicularia not observed.
Remarks
Rhagasostoma gibbosulum can be distinguished from R. gibbosum by the convex border of the cryptocyst and the inferred, well-developed gymnocyst.
Distribution
Middle Campanian United Kingdom: High Down, Isle of Wight, England. Late Campanian Belarus: Quarry near Hrodna / Grodno (Гродна/ Гродно), Grodno Region. Early Maastrichtian Germany: Saturn quarry, near Kronsmoor, Schleswig-Holstein.
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 35-38, DOI: 10.5852/ejt.2018.490, http://zenodo.org/record/3830845