Rhagasostoma gibbosum ( Marsson, 1887 )

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 : 31-35

Rhagasostoma gibbosum ( Marsson, 1887)

Figs 12–13 , Table 7

Eschara gibbosa Marsson, 1887: 71 , pl. 7, fig. 2.

Rhagasostoma subgibbosum Brydone, 1930: 48 , pl. 26, fig. 11. Syn. nov.

Rhagasostoma gibbosum var. weybournensis Brydone, 1930 pars: 48, pl. 26, figs 13–14. Syn. nov.

Rhagasostoma gibbosum –? Levinsen 1925: 369. — Brydone 1930: pl. 26, fig. 15.

Onychocella gibbosa –? Voigt 1930: 460, pl. l8, fig. 15. —? Veenstra 1963: 107, pl. fig. 5.

non Rhagasostoma gibbosum var. weybournensis – Brydone 1930 pars: 48, pl. 26, fig. 12.

Material studied

Figured material

GERMANY • 2 specs; Schleswig-Holstein, Saturn quarry near Kronsmoor; early Maastrichtian ; SMF 29906 ( Fig. 12 A–E), 29907 ( Fig. 12F ) .

UNITED KINGDOM • England, Norfolk; early Maastrichtian ( Ostrea lunata Zone ) of Trimingham ; SM B36679 ( Fig. 12G ; figured by Brydone 1930: pl. 26, fig. 15) .

BELARUS • 3 specs; Grodno Region; erratic block of?late Campanian age in a quarry near Hrodna / Grodno (Гродна/ Гродно); PIN 2922 /216 ( Fig. 13B ), 2922/218 ( Fig. 13A ), 2922/275 ( Fig. 13C ) .

KAZAKHSTAN • 2 specs; Emba River; late Campanian ( Belemnitella lanceolata Zone ); PIN 5502/3058 ( Fig. 13D ), 5502/3059 ( Fig. 13E ).

Other material

BELARUS • Grodno Region; erratic block of?late Campanian age in a quarry near Hrodna / Grodno (Гродна/ Гродно); PIN 2922 /274 .

Description

Colony erect, with flattened bifoliate branches (3–4 mm wide).Ancestrula and early astogeny not observed. Autozooids variable in shape, often broad and subrectangular with rounded distal ends; zooidal boundaries raised. Gymnocyst sometimes observed ( Figs 12G , 13E ). Cryptocyst extensive, finely pustulose, slightly depressed or slightly convex centrally, sometimes with proximal peripheral caverns ( Fig. 13B, C ). Opesia terminal, rarely subterminal, semielliptical with distal shelf, a thin inner wall delimiting the distolateral part of the opesia and a thickened, projecting outer wall delimiting the proximolateral part ( Figs 12C , 13C ). Proximal edge of opesia straight, smooth, thickened, with proximolateral outgrowths defining small opesiules at the corners; outgrowths often destroyed, giving opesiules the appearance of opesiular indentations. Septula not observed. Ovicells endozooidal, ooecium is formed by the distal zooid, wellrecognizable, with cryptocyst-like surface and arch-like proximal edge with elongated proximolateral processes extending along the cryptocyst of the maternal zooid ( Figs 12B, D, G , 13B , D–E). Avicularia interzooidal, smaller than autozooids, elongate. Rostrum channeled, symmetrical, with elevated winglike 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 the distal autozooid. Rostrum tilted over the proximal part of the distal autozooid or the ooecium of a maternal autozooid. Wedge-like structures present ( Fig. 12 B–D), extending from the base to the middle of the rostrum and partially covering the opesia, but often these structures are broken ( Fig. 12E ). Proximal part rounded, shorter and wider than rostrum, cryptocyst pustulose, concave, without peripheral caverns. Opesia roundish, with two short teeth proximally, opesiules lacking ( Fig. 12E ). Kenozooids subcircular, located along the branch margins ( Fig. 12A ). Cryptocyst finely pustulose, opesia roundish ( Figs 12C , 13A , D–E). Intramural reparative kenozooidal buds sometimes observed within host autozooids and avicularia ( Fig. 13 D–E), all with the same polarity as the host zooid. Closure plates, intramural reparative budding autozooids and avicularia not observed.

Remarks

The type material of Rhagasostoma gibbosum ( Marsson, 1887) could not be found, although part of the Marsson Collection has recently been recovered ( Martha 2014). From the similar species R. tchvanovi ( Favorskaya, 1992) , R. gibbosum differs in having a rostrum that is short and tilted to the right or left instead of being long and almost straight. Rhagasostoma gibbosum can be distinguished from R. gibbosulum by the slightly convex border of the cryptocyst and the very rare presence of a gymnocystal portion.

Distribution

Late Campanian Belarus: Quarry near Hrodna / Grodno (Гродна/ Гродно), Grodno Region. Kazakhstan: Emba River. Early Maastrichtian United Kingdom: Trimingham, Norfolk, England. Germany: Saturn quarry near Kronsmoor, Schleswig-Holstein, Island of Rügen, Mecklenburg-Vorpommern.Maastrichtian: unspecified localities in Denmark.

Figures

Fig. 12. Rhagasostoma gibbosum (Marsson, 1887). A–F. Early Maastrichtian, Saturn quarry near Kronsmoor, Schleswig-Holstein, Germany. A–E. SMF 29906. A. Overview of erect bifoliate colony. B. Ovicellate and non-ovicellate autozooids and avicularia. C. Autozooid, avicularium with wedge-like structureandkenozooid.D.Ovicellateautozooidsand aviculariawith wedge-likestructure.E.Avicularium with broken wedge-like structure. F. SMF 29907, autozooids and avicularia. G. SM B36679, Upper Chalk, early Maastrichtian, Ostrea lunata Zone, Trimingham, Norfolk, England, UK. Ovicellate and non-ovicellate autozooids, some with gymnocyst (arrowed), avicularia and kenozooids. Scale bars: A, F = 1 mm; B–D = 300 µm; E = 100 µm; G = 200 µm.

Fig. 13. Rhagasostoma gibbosum (Marsson, 1887). A–C. Erratic block of?late Campanian age, quarry near Hrodna/Grodno (Гродна/Гродно), Grodno Region, Belarus. A. PIN 2922/218, overview of erect bifoliate colony showing autozooids, avicularia and kenozooids. B. PIN 2922/216, autozooids with proximal peripheral caverns (Cv) and broken ooecium (arrowed), avicularia. C. PIN 2922/275, nonovicellate autozooids with proximal caverns and avicularia. D–E. Late Campanian (Belemnitella lanceolata Zone), Emba River, Kazakhstan. D. PIN 5502/3058, overview of erect bifoliate colony showing autozooids (some ovicellate), avicularia and kenozooids. E. PIN 5502/3059, non-ovicellate and ovicellate autozooids, some with gymnocyst (arrowed), and avicularia. Scale bars: A, D–E = 1 mm; B–C = 500 µm.

Tables

Table 7. Summary of measurements of Rhagasostoma gibbosum (Marsson, 1887). 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		British–Belgian– Dutch Early Maastrichtian Norfolk	North German Early Maastrichtian Kronsmoor	Polish–South Baltic?Late Campanian Grodno Region	North Ust-Yurt– Aral Late Campanian Emba River	Total
	AzL	420–690 (6) 523.33 ± 113.25	450–810 (12) 598.33 ± 99.89	410–640 (18) 511.67 ± 55.44	500–740 (12) 574.17 ± 70.12	410–810 (48) 550.42 ± 85.80
	AzW	350–420 (6) 391.67 ± 29.27	410–650 (12) 505.00 ± 67.62	340–430 (18) 379.44 ± 34.04	390–520 (12) 450.83 ± 36.55	340–650 (48) 430.21 ± 67.87
Autozooids	OpL OpW CvL GL	140–160 (6) 150–200 (12) 151.67 ± 7.53 173.33 ± 18.26 160–210 (6) 160–230 (12) 180.00 ± 20.00 198.33 ± 20.82 Not observed 180–220 (2) Not observed 200.00 ± 28.28		120–160 (17) 142.35 ± 12.00 140–180 (17) 161.18 ± 15.36 70–280 (15) 150.67 ± 59.10 200 (1)	170–210 (12) 185.83 ± 13.79 170–210 (12) 182.50 ± 12.88 Not observed 120–250 (4) 185.00 ± 56.86	120–210 (47) 162.55 ± 22.79 140–230 (47) 178.51 ± 22.06 70–280 (15) 150.67 ± 59.10 120–250 (7) 191.43 ± 42.59
	OoL	140–180 (6) 141.67 ± 33.12	190–300 (8) 246.25 ± 35.43	110–180 (6) 143.33 ± 27.33	190–270 (5) 242.00 ± 30.33	110–300 (25) 195.60 ± 60.14
	OoW	270–380 (6) 305.00 ± 38.86	360–450 (8) 410.00 ± 26.19	180–240 (6) 221.67 ± 22.29	200–480 (6) 343.33 ± 89.14	180–480 (26) 326.92 ± 85.03
	AvL	300–390 (5) 336.00 ± 35.78	310–460 (10) 365.00 ± 42.75	300–460 (16) 358.13 ± 45.49	330–490 (10) 413.00 ± 50.34	300–490 (41) 370.49 ± 50.54
	RL	190–310 (5) 244.00 ± 46.69	220–300 (11) 269.09 ± 28.09	190–300 (16) 240.00 ± 30.98	200–360 (10) 274.00 ± 53.17	190–360 (42) 256.19 ± 40.24
Avicularia	W–lSL RW PrL PrW	Not observed 100–180 (5) 130.20 ± 30.15 50–140 (5) 92.00 ± 32.71 100–180 (5) 126.00 ± 32.86	160–240 (6) 188.33 ± 29.94 90–160 (11) 122.73 ± 24.94 60–140 (11) 88.09 ± 23.54 70–150 (11) 107.27 ± 23.28	Not observed 80–180 (17) 90–170 (10) 134.71 ± 29.82 137.00 ± 26.69 80–160 (17) 100–150 (10) 110.59 ± 21.64 120.00 ± 18.86 70–180 (17) 90–170 (10) 138.82 ± 32.76 132.00 ± 33.60		160–240 (6) 188.33 ± 29.94 80–180 (43) 131.65 ± 27.52 50–160 (43) 104.86 ± 25.49 70–180 (43) 127.67 ± 32.35
	OpL	70 (1)	50–80 (2) 65.00 ± 21.21	40–100 (14) 83.57 ± 14.99	100 (1)	40–100 (18) 81.67 ± 16.18
	OpW	80 (1)	30–50 (2) 40.00 ± 14.14	40–100 (14) 78.57 ± 14.06	80 (1)	30–100 (18) 74.44 ± 17.90
Kenozooids	KzL KzW OpD	170–480 (4) 285.00 ± 135.28 170–300 (4) 222.25 ± 92.16 40–60 (4) 45.00 ± 10.00	120–380 (8) 272.50 ± 106.34 120–370 (8) 258.75 ± 97.31 20–50 (8) 31.25 ± 11.26	220–390 (7) 302.86 ± 86.93 130–370 (7) 244.29 ± 77.00 30–80 (7) 50.00 ± 22.04	340–580 (6) 471.67 ± 87.27 230–400 (6) 336.67 ± 61.86 20–60 (6) 40.00 ± 17.89	120–580 (25) 330.80 ± 125.43 120–200 (25) 267.56 ± 88.45 20–80 (26) 41.15 ± 17.51