Rhagasostoma minuens 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 minuens

description: Rhagasostoma minuens Brydone, 1936
Figs 6–7, Table 3
Rhagasostoma inelegans var. minuens Brydone, 1936: 74, pl. 35, figs 9–10.
Onychocella cf. inelegans (Lonsdale, 1850) – Voigt 1949: 26, pl. 8, figs 1–2.
Material studied
Lectotype (here designated)
UNITED KINGDOM • England, East Sussex, between Brighton and Roedean; late Santonian (Uintacrinus socialis Zone / lower Marsupites testudinarius Zone); SM B36883 (Fig. 6 A–D; figured by Brydone 1936: pl. 35, fig. 10).
Paralectotype (here designated)
UNITED KINGDOM • England, Norfolk, Trimingham; early Maastrichtian (Ostrea lunata Zone, Porosphaera Beds); SM B36882 (Fig. 6 E–F; figured by Brydone 1936: pl. 35, fig. 9).
Additional figured material
UNITED KINGDOM • 2 specs; England, Kent; Coniacian of Chatham; SMF 29921 (Fig. 7 A–B), 29922 (Fig. 7 C) • England, Wiltshire, SW of Salisbury, Harnham; early Campanian; SMF 29920 (Fig. 7D) • England, Norfolk, Trimingham; early Maastrichtian (Ostrea lunata Zone) [middle Campanian (Belemnitella mucronata Zone), Weybourne, Norfolk, in SM database]; SM B 36678, specimen (a) (Fig. 7 H) • 2 specs; England, East Sussex, Newhaven, Meeching Quarry; early Campanian; SMF 29943 (Fig. 7 E), 29944 (Fig. 7 F).
FRANCE • Hanches; Campanian; SMF 29918 (Fig. 7 G).
Other material
UNITED KINGDOM • 3 specs; England, East Sussex, Newhaven, Meeching Quarry; early Campanian; SMF 29919, 29942, 29945.
GERMANY • Schleswig-Holstein, Lägerdorf; early Campanian; SMF 29917.
Description
Colony encrusting sheet-like, fragments about 10 mm in diameter, or erect with flattened bifoliate branches, fragments up to 2.0–10.0 mm long by 2.0–5.0 mm wide. Ancestrula (Fig. 6C) about 0.27 mm in diameter, rounded rhombic. Autozooids variable in shape, often broad and subrectangular with rounded distal ends; zooidal boundaries raised. Gymnocyst lacking. Cryptocyst extensive, finely pustulose,
depressed or slightly convex centrally, sometimes with proximolateral peripheral caverns, up to 0.22 mm long (Fig. 7 B–F), rarely peripheral caverns surrounding the cryptocyst (Fig. 7H). Opesia terminal, rarely subterminal, semielliptical with slight shelf in the distal part (Fig. 6D, F), formed by two walls, a thin inner wall delimiting the distolateral part and a salient, thickened outer wall delimiting the proximolateral part. Proximal edge of opesia straight, smooth, thickened, with outgrowths near the two proximolateral corners delimiting, small roundish opesiules (outgrowths are often broken thus giving the opesiules the appearance of opesiular indentations, or they may be obscured by sediment infills of the opesia). Septula not observed. Ovicells endozooidal, ooecium is formed by the distal zooid, recognizable as a small swelling of its proximal cryptocyst (Figs 6D, 7C, E–F). Avicularia interzooidal, elongate, longer than autozooids. Rostrum channeled with elevated wing-like walls and pointed tip, falciform (almost the same width along the whole length of the rostrum or slightly expanding near apex, and pointed tip curved, sickleshaped), asymmetrical, dextral or sinistral. Proximal part rounded, shorter and wider than the rostrum. Cryptocyst pustulose, concave, without peripheral caverns. Opesia large, roundish or oval, with thickened articular ridges bearing two short teeth proximally and a long, slit-like opesiular indentation between the teeth; opesiules lacking. Kenozooids rounded, rare, located at the margins of a colony. Cryptocyst finely pustulose. Opesia round. Intramural reparative budding of avicularia within host avicularia sometimes observed (Fig. 7B), all with the same polarity as the host zooid. Intramural reparative kenozooidal buds sometimes observed within host autozooids and avicularia (Fig. 7 D–E). Closure plates not observed.
Remarks
Brydone (1936) introduced the subspecies Rhagasostoma inelegans minuens for unilaminar colonies lacking ovicells. We have restudied Brydone’s syntypes in the SM collection, choosing a lectotype (the specimen figured by Brydone 1936: pl. 35, fig. 10); endozooidal ovicells are present in this colony. Voigt (1949) mentioned one specimen of “ Onychocella cf. inelegans ” from the early Campanian of Lägerdorf, Schleswig-Holstein of Germany but this belongs to Rhagasostoma minuens.
Rhagasostoma minuens can easily be distinguished from R. inelegans, R. brydonei sp. nov., R. aralense sp. nov. and R. operculatum sp. nov. in having a falciform avicularian rostrum. The species differs from R. angliae, specimens of which may have similar falciform avicularian rostra, in the avicularian cryptocyst having large roundish or oval opesia without opesiules instead of small subcircular opesia and two opesiules.
Distribution
Coniacian United Kingdom: Chatham, Kent, England. Late Santonian United Kingdom: between Brighton and Roedean, East Sussex, England. Early Campanian United Kingdom, England: Harnham, SW of Salisbury, Wiltshire; Meeching Quarry, Newhaven, East Sussex. Germany: Lägerdorf, Schleswig-Holstein. Campanian France: Hanches. Early Maastrichtian United Kingdom: Trimingham, Norfolk, England.
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 16-20, DOI: 10.5852/ejt.2018.490, http://zenodo.org/record/3830845