Rhagasostoma angliae Brydone, 1936

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 : 20-25

Rhagasostoma angliae Brydone, 1936

Figs 8–9 , Table 4

Rhagasostoma inelegans var. angliae Brydone, 1936 pars: 74, pl. 35, figs 4,?5, 6–7.

Onychocella dichotoma (Goldfuss, 1826) – Voigt 1949: pl. 8, fig. 3.

non Rhagasostoma inelegans var. angliae – Brydone 1936 pars: 74, pl. 35, fig. 8.

Material studied

Lectotype (here designated)

UNITED KINGDOM • England, Norfolk, Norwich; Middle Campanian ( Belemnitella mucronata Zone ) of Hartford; SM B36877 ( Fig. 8 A–E; figured by Brydone 1936: pl. 35, fig. 4).

Paralectotype (here designated)

UNITED KINGDOM • England, Norfolk; early Maastrichtian ( Ostrea lunata Zone ) of Trimingham; SM B36879 ( Fig. 8 F–H; figured by Brydone 1936: pl. 35, figs 6–7).

Additional figured material

UNITED KINGDOM • England, Norfolk; middle Campanian ( Belemnitella mucronata Zone ) of Weybourne; SM B36671 ( Fig. 9 A–C).

FRANCE • Île-de-France; late Campanian of Vigny ; SMF 29914 ( Fig. 9 D–E) .

GERMANY • Early Maastrichtian of Hemmoor ; SMF 26288 ( Fig. 9 F–G; figured by Voigt 1949: pl. 8, fig. 3) .

Description

Colony encrusting, sheet-like, fragments up to 10 mm in diameter, or erect with flattened, bifoliate branches, fragments up to 6.0–7.0 mm long by 3.0–5.0 mm wide. Ancestrula ( Fig. 8B ) about 0.33 mm in diameter, rounded rhombic, surrounded by six periancestrular zooids, five zooids possibly budded directly from the ancestrula. Autozooids variable in shape, often broad and roughly rectangular with rounded distal ends; zooidal boundaries raised. Gymnocyst lacking. Cryptocyst extensive, finely pustulose, depressed or slightly convex centrally, sometimes with peripheral cavern surrounding the cryptocyst ( Fig. 8C ). Opesia terminal or subterminal, semielliptical with shelf distally, formed by two walls, a thin inner wall delimiting the distolateral part and a salient, thickened outer wall delimiting the proximolateral part ( Figs 8E, H , 9C ). Proximal edge of opesiae straight, smooth, thickened, with outgrowths near the two proximolateral corners delimiting small, roundish opesiules (outgrowths are often broken, giving the opesiules the appearance of opesiular indentations, or they may be obscured by sediment fillings inside the opesia). Septula not observed. Ovicells endozooidal, ooecium is formed by the distal zooid, ill-recognizable, with cryptocyst-like surface ( Fig. 9E ). Avicularia interzooidal, longer than autozooids, elongate. Rostrum channeled with elevated wing-like walls and pointed tip, conical in outline or sometimes falciform, asymmetrical, dextral or sinistral. Proximal part rounded, shorter and slightly wider than the rostrum. Cryptocyst pustulose, concave with depression centrally, sometimes with peripheral cavern surrounding the cryptocyst ( Fig. 8C, E, H ), having three openings: a distal small subcircular opesia; two lateral and parallel slit-like opesiules formed by long teeth of articular ridges, which grow together with proximal edge of opesia; a long and slit-like opesiular indentation proximally between the teeth ( Figs 8E, H , 9C, E, G ). Cryptocyst between openings frequently destroyed, causing the openings to coalesce into a single opening of variable outline that is sometimes tulip-shaped. Kenozooids rounded, very rare, located at the margins of a colony or between zooids ( Fig. 9D ). Cryptocyst finely pustulose. Opesia roundish, small. Closure plates, intramural reparative budding in autozooids and avicularia not observed.

Remarks

Brydone (1936) introduced the subspecies Rhagasostoma inelegans angliae 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. 4). The specimen figured by Brydone (1930: pl. 26, fig. 5) was not restudied.

Brydone (1936) compared his specimens of Rhagasostoma inelegans angliae from the Trimingham Chalk with the bilaminar, ovicellate Onychocella dichotoma sensu Levinsen (1925) from the early Maastrichtian white Chalk of southeastern Denmark and northern Jylland. However, Levinsen’s drawing shows that his species has an avicularian opesiae similar to Rhagasostoma inelegans incarcerata sensu Brydone (1930) . The avicularia of this subspecies apparently contain two pairs of lateral, parallel, slit-

like opesiules in the central part of the cryptocyst, whereas angliae has only one pair of lateral, parallel, slit-like opesiules. Voigt (1949: 26) mentioned one specimen from the late Campanian ( Belemnitella lanceolata Zone ) of Hemmoor. Our study shows that the avicularian opesia in this specimen are similar to angliae , while Voigt (1949) described it as Onychocella dichotoma Goldfuss, 1826 and classified O. inelegans incarcerata as a junior synonym of O. dichotoma .

Rhagasostoma angliae can easily be distinguished from R. inelegans , R. brydonei sp. nov., R. minuens , R. aralense sp. nov. and R. operculatum sp. nov. as the avicularian cryptocysts have small, subcircular opesia and two opesiules instead of large, roundish or oval opesia without opesiules. Rhagasostoma rowei ( Brydone, 1906) and R. mimosa ( Brydone, 1930) also have avicularian cryptocysts with small subcircular opesia and opesiules, but R. angliae differs from these species in having articular ridges bearing teeth with proximal opesiular indentation between the teeth and interzooidal, and elongate avicularia with asymmetrical rostra instead of vicarious, rhomboidal avicularia with symmetrical rostra.

Distribution

Middle Campanian United Kingdom: Norwich and Weybourne, Norfolk, England ( Brydone 1936). Late Campanian France: Vigny, Île-de-France. Early Maastrichtian Germany: Hemmor ( Voigt 1949). United Kingdom: Trimingham, Norfolk, England.

Figures

Fig. 8. Rhagasostoma angliae (Brydone, 1936). A–E. Lectotype, SM B36877, Middle Campanian (Belemnitella mucronata Zone) of Hartford, Norwich, Norfolk, England, UK. A. Overview of encrusting colony. B. Early astogeny, ancestrula arrowed. C. Growing edge, avicularia and some autozooids with peripheral caverns surrounding the cryptocyst. D. Autozooids and avicularia. E. Avicularium with peripheral caverns surrounding the cryptocyst and non-ovicellate autozooids. F–H. Paralectotype, SM B36879, early Maastrichtian (Ostrea lunata Zone) of Trimingham, Norfolk, England, UK. F. Erect bifoliate colony. G. Non-ovicellate autozooids and avicularia. H. Avicularia and non-ovicellate autozooids. Scale bars: A, F = 1 mm; B, E, H = 100 µm; C–D, G = 200 µm.

Fig. 9. Rhagasostoma angliae Brydone, 1936. A–C. SM B36671, Middle Campanian (Belemnitella mucronata Zone), Weybourne, Norfolk, England, UK. A. Overview of erect bifoliate colony. B. Nonovicellate autozooids and avicularia. C. Opesiae of non-ovicellate autozooids with distal shelf and avicularium. D–E. SMF 29914, Late Campanian of Vigny, Île-de-France, France. D. Overview of erect bifoliate colony. E. Non-ovicellate and one ovicellate (with partially broken ooecium, arrowed) autozooids and avicularia. F–G. SMF 26288, early Maastrichtian of Hemmor, Germany. F. Overview of erect bifoliate colony. G. Non-ovicellate autozooids and avicularia. Scale bars: A, D = 1 mm; B, G = 200 µm; C = 100 µm; E = 300 µm; F = 2 mm.

Tables

Table 4. Summary of measurements of Rhagasostoma angliae Brydone, 1936. For each parameter the range is given with the number of measurements in brackets. The arithmetic mean is given ± standard deviation. All measurements in µm.

Basin Stratigraphy Locality		Southern North Sea Basin Middle Campanian to early Maastrichtian Norwich, Weybourne, Trimingham, Vigny	North German Basin Early Maastrichtian Hemmor	Total
	AzL	460–700 (24) 568.33 ± 64.92	600–700 (6) 656.67 ± 39.33	460–700 (30) 586.00 ± 70.00
	AzW	340–530 (24) 418.33 ± 53.46	400–540 (6) 465.00 ± 52.44	340–540 (30) 427.67 ± 55.69
Autozooids	CvL OpL OpW	140–220 (24) 185.42 ± 19.11 160–230 (24) 195.42 ± 21.26	Not observed 160–190 (6) 170.00 ± 10.95 150–210 (6) 166.67 ± 24.22	140–220 (30) 182.33 ± 18.70 150–230 (30) 189.67 ± 24.42
	OoL OoW	270 (1) 350 (1)	Not observed	270 (1) 350 (1)
	AvL	690–1050 (23) 801.74 ± 96.18	800–1060 (5) 936.00 ± 143.63	690–1060 (28) 825.71 ± 115.48
	RL	430–580 (23) 503.48 ± 46.08	460–710 (5) 568.00 ± 97.83	430–710 (28) 515.00 ± 61.49
Avicularia	RCL RW PrL	170–300 (11) 218.18 ± 36.01 120–170 (23) 146.52 ± 14.34 210–470 (23) 286.09 ± 70.82	150–260 (4) 177.50 ± 60.21 150–250 (5) 200.00 ± 43.01 290–450 (5) 354.00 ± 75.03	150–300 (15) 207.33 ± 45.27 120–250 (28) 156.07 ± 29.61 210470 (28) 298.21 ± 74.98
	PrW	200–320 (23) 246.96 ± 25.12	270–340 (5) 300.00 ± 29.15	200–340 (28) 256.43 ± 32.68
	OpD	20–40 (16) 29.69 ± 5.31	?	20–40 (16) 29.69 ± 5.31
Kenozooids	KzL KzW OpD	260–620 (4) 360.00 ± 173.59 220–350 (4) 267.50 ± 57.37 70 (4) 70.00 ± 0.00	Not observed	260–620 (4) 360.00 ± 173.59 220–350 (4) 267.50 ± 57.37 70 (4) 70.00