Rhagasostoma brydonei, 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 : 13-16

Rhagasostoma brydonei sp. nov.

urn:lsid:zoobank.org:act:B229DB57-799E-494C-95EF-7F117080B3E9

Fig. 5 , Table 2

Rhagasostoma inelegans ( Lonsdale, 1850) – Brydone 1930 pars: 47, pl. 25, figs 11–12.

non Rhagasostoma inelegans – Brydone 1930 pars: 47, pl. 26, figs 1–3.

Diagnosis

Colony erect, bifoliate. Autozooids rectangular, zooidal boundaries raised; gymnocyst lacking; cryptocyst extensive with peripheral caverns; opesia terminal, rarely subterminal, semielliptical with shelf in the distal part, proximal edge with small roundish opesiules; ovicells immersed, ooecia vestigial. Avicularia interzooidal, longer than autozooids; rostrum channeled with pointed tip, spade-shaped, symmetrical or asymmetrical; proximal part rounded, shorter and wider than rostrum; opesia oval or roundish with thickened articular ridges bearing two very short teeth proximally and a long, slit-like opesiular indentation between the teeth; opesiules lacking. Kenozooids rare, rounded or oval.

Etymology

In honour of Reginald Marr Brydone (1873 – 1943), a prolific author of bryozoan species from the English Chalk and collector of the type material of the new species.

Material studied

Holotype

UNITED KINGDOM • England, Hampshire, south of Alton, Froxfield , Kings Lane ; latest Turonian ( Sternotaxis plana Zone ); SM B 36666 ( Fig. 5 A–B; figured by Brydone 1930: pl. 25, figs 11–12).

Paratypes

UNITED KINGDOM • Same data as for holotype; SM B 36667 ( Fig. 5 C–D) • 3 specs; England, Kent; Coniacian of Chatham ; SMF 29939 ( Fig. 5F ), 29940 ( Fig. 5E ), 29941 ( Fig. 5 G–H) .

Type locality and horizon

United Kingdom, England, Hampshire, south of Alton, Froxfield, Kings Lane; Sternotaxis plana Zone , late Turonian.

Description

Colony usually erect, with flattened bifoliate branches, fragments 3.5–6.0 mm long by 2.0– 6.5 mm wide. Ancestrula and early astogeny not observed. 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, with peripheral caverns surrounding the cryptocyst ( Fig. 5B, D , F–H) or rarely developed in proximal or proximolateral part of cryptocyst ( Fig. 5E ). Opesia terminal, rarely subterminal, semielliptical, with shelf in the distal part, formed by two walls, a thin inner wall delimiting the distolateral part and a salient, thickened outer wall delimiting the proximolateral part ( Fig. 5H ). 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 immersed, ooecium formed by the distal zooid, vestigial, vizor-like, brooding

cavity located in the distal part of the maternal zooid and below the colony surface ( Fig. 5H ). Avicularia interzooidal, elongate, longer than autozooids. Rostrum channelled, with elevated wing-like walls and pointed tip, spade-shaped, symmetrical or asymmetrical, dextral or sinistral. Proximal part rounded, shorter and wider than rostrum. Cryptocyst pustulose, concave, peripheral caverns rare. Opesia large, usually oval, rarely roundish, with thickened articular ridges bearing two very short teeth proximally and a long, slit-like opesiular indentation between teeth; opesiules lacking. Kenozooids rounded or oval, located usually at edges of colony ( Fig. 5B ). Cryptocyst finely pustulose with proximal peripheral caverns. Opesia roundish, small. Closure plates, intramural reparative budding of zooids not observed.

Remarks

We have restudied Brydone’s examples of Rhagasostoma inelegans in the SM collection. The specimen identified by Brydone as this species ( Brydone 1930: pl. 25, figs 11, 12) does not belong to Lonsdale’s species and is here regarded as a new species, R. brydonei sp. nov.

The new species differs from the closely related species Rhagasostoma inelegans , R. minuens , R. angliae and R. aralense sp. nov. in the avicularian rostrum being spade-shaped rather than having a conical outline shape or falciform. Moreover, the ovicells of R. brydonei sp. nov. are immersed. Rhagasostoma brydonei sp. nov. differs from R. angliae in having an avicularian cryptocyst with large oval or roundish opesia lacking opesiules, instead of a small subcircular opesia and two opesiules. The new species differs from R. operculatum sp. nov., which has a similar spade-shaped avicularian rostrum, by the rostrum being narrowed at the base, enlarged centrally and with a pointed tip, instead of being the same width along almost its entire length and having a pointed or rounded tip.

Distribution

Late Turonian United Kingdom: Kings Lane, Froxfield, south of Alton, Hampshire, England. Coniacian United Kingdom: Chatham, Kent, England.

Figures

Fig. 5. Rhagasostoma brydonei sp. nov. A–D. Latest Turonian (Sternotaxis plana Zone), Kings Lane, Froxfield, south of Alton, Hampshire, England, UK. A–B. Holotype, SM B36666. A. Overview of erect bifoliate colony. B. Autozooids (Az) and kenozooids (Kz) with peripheral caverns (arrowed) and avicularia. C–D. Paratype SM B36667. C. Overview of erect bifoliate colony. D. Autozooids with peripheral cavern surrounding the cryptocyst (arrowed) and avicularia. E–H. Coniacian, Chatham, Kent, England, UK. E. Paratype, SMF 29940, autozooids with proximal peripheral caverns (arrowed) and avicularia. F. Paratype, SMF 29939, autozooids with peripheral cavern surrounding the cryptocyst and avicularia. G–H. Paratype, SMF 29941. G. Autozooids with peripheral cavern surrounding the cryptocyst and avicularia. H. Autozooids with peripheral cavern surrounding the cryptocyst and ooecia of immersed ovicells (arrowed) and avicularia. Scale bars: A, D, H = 200 µm; B = 100 µm; C, F = 1 mm; E, G = 500 µm.

Tables

Table 2. Summary of measurements of Rhagasostoma brydonei sp. nov. 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 Late Turonian to Coniacian Hampshire, Kent
	AzL	440–620 (18) 541.67 ± 55.65
	AzW	280–470 (18) 368.33 ± 46.94
Autozooids	CvL OpL OpW	80–180 (16) 120.00 ± 31.83 80–180 (18) 150.56 ± 25.32 140–190 (18) 168.89 ± 12.78
	OoL	10–30 (5) 20.00 ± 7.07
	OoW	50–110 (5) 76.00 ± 21.91
	AvL	610–880 (16) 705.00 ± 73.48
	RL	350–460 (16) 406.25 ± 34.03
Avicularia	RW PrL PrW	140–200 (16) 173.13 ± 15.80 220–440 (16) 298.75 ± 53.77 180–300 (16) 226.88 ± 31.77
	OpL	70–150 (15) 112.67 ± 25.20
	OpW	70–130 (15) 90.00 ± 14.64