Rhagasostoma gibbosulum 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 : 35-38

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. 14G ), 29909 ( Fig. 14H ), 29911 ( Fig. 14I ), 29912 ( Fig. 14J ) .

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.

Figures

Fig. 14. Rhagasostoma gibbosulum Brydone, 1936. A–D. Holotype, SM B36887, middle Campanian (Belemnitella mucronata Zone) of Isle of Wight, High Down, England, UK. A. Overview of erect bifoliate colony. B. Non-ovicellate autozooids and avicularia. C. Opesia of autozooid. D. Avicularium. E–F. PIN 2922/242, erratic block of?late Campanian age, quarry near Hrodna/Grodno (Гродна/ Гродно), Grodno Region, Belarus. E. Overview of erect bifoliate colony. F. Non-ovicellate autozooids and avicularia. G–J. Early Maastrichtian, Saturn quarry near Kronsmoor, Schleswig-Holstein, Germany. G. SMF 29908, overview of part of erect bifoliate colony. H. SMF 29909, autozooids, avicularia and kenozooids. I. SMF 29911, non-ovicellate autozooid with long gymnocyst(?), two ovicellate autozooids (with non-damaged ooecium to the right), and avicularium with wedge-like growth. J. SMF 29912, non-ovicellate autozooids and avicularia, one from which with wedge-like growth. Scale bars: A, E, G = 1 mm; B = 100 µm; C–D = 20 µm; F = 500 µm, H–J = 300 µm.

Tables

Table 8. Summary of measurements of Rhagasostoma gibbosulum 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 Early Maastrichtian Norfolk	North German Basin Early Maastrichtian Kronsmoor	Polish Basin?Late Campanian Grodno Region	Total
	AzL	330–510 (6) 420.00 ± 75.37	410–880 (18) 558.33 ± 108.97	390–480 (6) 435.00 ± 32.09	330–880 (30) 506.00 ± 111.31
	AzW	240–320 (6) 283.33 ± 27.33	320–520 (18) 416.11 ± 45.26	260–360 (6) 316.67 ± 35.02	240–520 (30) 369.67 ± 70.73
Autozooids	OpL OpW GL	80–110 (6) 100.00 ± 12.65 110–140 (6) 126.67 ± 13.66 60–130 (6) 100.00 ± 29.66	80–140 (18) 108.89 ± 16.05 110–150 (18) 131.67 ± 14.65 50–370 (18) 152.78 ± 79.40	90–130 (6) 106.67 ± 13.66 120–130 (6) 126.67 ± 5.16 50–120 (3) 80.00 ± 36.06	80–140 (30) 106.67 ± 14.93 110–150 (30) 129.67 ± 12.99 50–370 (27) 132.96 ± 72.37
	OoL OoW	Not observed	260–270 (3) 263.33 ± 5.77 230–360 (3) 293.33 ± 65.06	Not observed	260–270 (3) 263.33 ± 5.77 230–360 (3) 293.33 ± 65.06
	AvL	160–270 (6) 226.67 ± 37.24	250–470 (14) 367.86 ± 76.98	320–390 (6) 320.00 ± 47.33	160–470 (26) 324.23 ± 84.62
	RL	90–180 (6) 141.67 ± 32.51	170–390 (14) 267.14 ± 69.22	140–240 (6) 193.33 ± 39.83	90–390 (26) 221.15 ± 76.85
	W–lSL	Not observed	140–190 (6) 160.00 ± 16.73	Not observed	140–190 (6) 160.00 ± 16.73
Avicularia	RW PrL	70–140 (6) 93.33 ± 25.03 70–140 (6) 95.00 ± 25.88	70–140 (14) 105.71 ± 20.65 70–190 (14) 114.29 ± 33.22	80–120 (6) 98.33 ± 14.72 70–140 (6) 105.00 ± 26.65	70–140 (26) 101.15 ± 20.46 70–190 (26) 107.69 ± 30.24
	PrW	60–130 (6) 91.67 ± 29.27	70–150 (14) 104.29 ± 23.11	90–130 (6) 101.67 ± 16.02	60–150 (26) 100.77 ± 22.96
	OpL OpW	Not observed	40–80 (8) 61.25 ± 12.46 30–70 (8) 52.50 ± 16.69	40–80 (4) 55.00 ± 19.15 40–70 (4) 47.50 ± 15.00	40–80 (12) 59.17 ± 14.43 30–70 (12) 50.83 ± 15.64
Kenozooids	KzL KzW OpD	380–400 (2) 390 ± 14.14 270–300 (2) 285.00 ± 21.21 20–30 (2) 25.00 ± 7.07	180–370 (14) 261.43 ± 67.24 180–390 (14) 272.86 ± 69.99 20–40 (15) 24.67 ± 6.40	130–270 (4) 207.50 ± 64.49 130–200 (4) 172.50 ± 29.86 20–60 (4) 30.00 ± 20.00	130–400 (20) 263.50 ± 78.15 130–390 (20) 254.00 ± 72.65 20–60 (21) 25.71 ± 9.78