Rhagasostoma inelegans ( Lonsdale, 1850 )

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 : 8-12

Rhagasostoma inelegans ( Lonsdale, 1850)

Figs 3–4 , Table 1

Flustra ? inelegans Lonsdale, 1850: 319 , pl. 18.B, figs 9,?10, 11.

Rhagasostoma inelegans var. angliae Brydone, 1936 pars: 74, pl. 35, fig. 8. Syn. nov.

Rhagasostoma inelegans – Brydone 1930 pars: 47, pl. 26, figs?1, 2–3.

Onychocella inelegans – Voigt 1975: 245, pl. 5, figs 1–4. — Taylor 1991: 33, pl. 7, fig. 9. — Taylor 2002: 70, pl. 9, fig. 9.

non Rhagasostoma inelegans – Brydone 1930 pars: 47, pl. 25, figs 11–12.

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

Material studied

Lectotype (here designated)

UNITED KINGDOM • England ; Chalk (?Santonian) of Sussex ; NHMUK D2967 ( Fig. 3 A–C; figured by Lonsdale 1850: pl. 18. B, fig. 9).

Paralectotype (here designated)

UNITED KINGDOM • same data as for lectotype; NHMUK D2959 ( Fig. 3D ; figured by Lonsdale 1850: pl. 18.B, fig. 11) .

Additional figured material

UNITED KINGDOM • England, Sussex coast; late Santonian ( Marsupites testudinarius Zone ); SM B36881 ( Fig. 3 E–G; figured by Brydone 1936: pl. 35, fig. 8) • England, Hampshire, near Winchester, Owslebury , Hensting Farm ; early Campanian ( Goniotheutis quadrata Zone ); SM B36669 ( Fig. 3 H–J; figured by Brydone 1930: pl. 26, figs 2–3).

GERMANY • Lower Saxony, Sehnde-Höver, Alemannia quarry; early Campanian ; SMF 24564 ( Fig. 4 A–B; figured by Voigt 1975: pl. 5, figs 1, 3–4 as coll. Voigt no. 7381) • Same data as for preceding; SMF 29915 ( Fig. 4 C ).

BELARUS • 2 specs; Grodno Region, quarry near Hrodna / Grodno (Гродна/ Гродно); erratic block of?late Campanian age; PIN 2922 /219 ( Fig. 4 D ), 2922/273 ( Fig. 4 E–F).

Other material

GERMANY • Lower Saxony, Sehnde-Höver, Alemannia quarry; early Campanian ; SMF 29916.

BELARUS • 2 specs; Grodno Region, quarry near Hrodna / Grodno (Гродна/ Гродно); erratic block of?late Campanian age; PIN 2922 /217, 2922/250.

Description

Colony usually erect, with flattened bifoliate branches, fragments 2.0–7.0 mm long by 2.5–5.5 mm wide; encrusting sheet-like colonies, measuring up to 5.0–7.0 mm long by 3.5–7.0 mm wide. Ancestrula and early astogeny not observed. Autozooids variable in shape, often broad, 6-sided and rhomboidal with rounded distal ends, zooidal boundaries raised. Gymnocyst lacking. Cryptocyst extensive, finely pustulose, depressed or slightly convex centrally, sometimes with proximal or proximolateral peripheral caverns, up to 0.17 mm long ( Fig. 3 D–G; and Taylor 1991, 2002). Opesiae terminal, rarely subterminal, semielliptical with narrow 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. 3J ). Proximal edge of opesia straight, smooth, thickened, with outgrowths near the two proximolateral corners delimiting, small round 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, brooding cavity located within the proximal part of the distal zooid ( Figs 3C, I , 4A– D); 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. Avicularia interzooidal, longer than autozooids, elongate ( Figs 3C , I–J, 4F). Rostrum channelled, with elevated wing-like walls and pointed apex, conical in outline, asymmetrical, dextral or sinistral. Proximal part rounded, shorter and wider than rostrum. Cryptocyst pustulose, concave, sometimes with proximal peripheral caverns ( Fig. 3E ). Opesia large, usually roundish, rarely oval, with thickened distolateral edge and with thin articular ridges bearing two short teeth in the proximal margin and a slit-like opesiular indentation between the teeth; opesiules lacking. Kenozooids round, located at edges of colonies ( Fig. 4A , C–D). Cryptocyst finely pustulose, peripheral caverns not observed. Opesia roundish, small. Intramural reparative budding of autozooids and avicularia sometimes observed ( Fig. 4C, F ), all with the same polarity as the host zooid. Closure plates and reparative budding kenozooids not observed.

Remarks

We have restudied Lonsdale’s syntypes in the NHMUK collection, choosing a lectotype (the bifoliate specimen figured by Lonsdale 1850: pl. 18.B, fig. 9), as well as material from the collections of R.M. Brydone, E. Voigt, and T.A. Favorskaya. One specimen identified by Brydone as O. inelegans ( Brydone 1930: pl. 26, figs 2, 3) does indeed belong to this species, while another ( Brydone 1930: pl. 25, figs 11, 12) is regarded as a new species, Rhagasostoma brydonei sp. nov. The specimen figured by Brydone (1930: pl. 26, fig. 1) was not restudied. The specimen described by Brydone (1936: pl. 35, fig. 8) as belonging to the subspecies O. inelegans angliae ( Brydone, 1936) is conspecific with Lonsdale’s encrusting sheet-like colony of R. inelegans . Favorskaya (1992, 1996) mentioned three specimens of this species from Campanian deposits in Uzbekistan and Turkmenistan, which according to our studies comprise two species: R. aralense sp. nov. ( Favorskaya 1992: 125, pl. 64, fig. 6, pl. 65, fig. 1) and R. operculatum sp. nov. ( Favorskaya 1992: pl. 64, fig. 7; 1996: pl. 3, fig. 4).

Rhagasostoma inelegans can be easily distinguished from R. brydonei sp. nov., R. minuens Brydone, 1936 and R. operculatum sp. nov. in having an avicularian rostrum conical in outline rather than spade-shaped or falciform. It further differs from R. brydonei sp. nov. by having endozooidal ovicells instead of immersed ovicells. Rhagasostoma inelegans differs from R. angliae in that the avicularian cryptocyst has a large roundish or oval opesia lacking opesiules, instead of a small subcircular opesia with two opesiules. It differs from R. aralense sp. nov., which also has an avicularian rostrum conical in outline, by the rostrum being asymmetrical instead of symmetrical, and the avicularian opesia roundish rather than egg-shaped.

Distribution

Late Santonian United Kingdom: Coast of Sussex, England. Early Campanian Germany: Alemannia quarry, Sehnde-Höver, Lower Saxony; Lahstedt-Oberg, Lower Saxony (according to Voigt 1949, 1975). United Kingdom: Hensting Farm, Owslebury, Hampshire, England. Late Campanian Belarus: Quarry near Hrodna / Grodno (Гродна/ Гродно), Grodno Region.

Figures

Fig. 3 (opposite page). Rhagasostoma inelegans (Lonsdale, 1850). A–D. Late Senonian, Sussex, England, UK. A–C. Lectotype, NHMUK D2967. A. Overview of erect bifoliate colony. B. Autozooids, avicularia, and endozooidal ovicells with ooecia having proximolateral processes. C. Avicularium. D. Paralectotype NHMUK D2959, overview of sheet-like colony; peripheral caverns arrowed. E–G. SM B36881, late Santonian (Marsupites testudianarius Zone) along the coast of Sussex, England, UK. E. Non-ovicellate autozooids and avicularia; peripheral caverns arrowed. F. Overview of encrusting sheet-like colony; peripheral caverns arrowed. G. Growing edge. H–J. SM B36669, early Campanian (Goniotheutis quadrata Zone), Hensting Farm, Owslebury, Hampshire, England, UK. H. Overview of erect bifoliate colony. I. Autozooids with endozooidal ovicells, avicularia and kenozooids. J. Opesia of non-ovicellate autozooid. Scale bars: A, H = 1 mm; B–C, I = 100 µm; D–G = 200 µm; J = 30 µm.

Fig. 4. Rhagasostoma inelegans (Lonsdale, 1850). A–C. Early Campanian, Alemannia quarry, Sehnde- Höver, Lower Saxony, Germany. A–B. SMF 24564. A. Distal part of erect bifoliate colony. B.Autozooids and avicularia (ooecia of endozooidal ovicells are clearly visible). C. SMF 29915, fragment of erect bifoliate colony with rare ovicellate autozooids, intramural non-ovicellate autozooid within autozooid and intramural avicularia within avicularia (arrowed). D–F. Erratic block of Campanian age, quarry near Hrodna/Grodno (Гродна/Гродно), Grodno Region, Belarus. D. PIN 2922/219, overview of erect bifoliate colony with row of three ovicellate autozooids, one with a broken ooecium, and avicularia. E–F. PIN 2922/273. E. Autozooid with broken ooecium, avicularia and non-ovicellate autozooids. F. Intramural non-ovicellate autozooid within autozooid and intramural avicularium within avicularium, and normal avicularium. Scale bars: A, C–D = 1 mm; B = 300 µm; E = 500 µm; F = 200 µm.

Tables

Table 1. Summary of measurements of Rhagasostoma inelegans (Lonsdale, 1850). 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 Santonian to early Campanian Sussex, Hampshire	North German Basin Early Campanian L. Saxony	Polish Basin?Late Campanian Grodno Region	Total
	AzL	300–600 (24) 475.42 ± 59.71	510–830 (12) 630.83 ± 97.56	470–580 (17) 520.59 ± 35.44	300–830 (53) 525.09 ± 87.76
	AzW	270–480 (24) 356.67 ± 54.75	410–620 (12) 510.00 ± 73.61	340–470 (16) 390.63 ± 37.50	270–620 (52) 402.50 ± 81.77
Autozooids	CvL OpL OpW	40–170 (12) 94.17 ± 37.77 140–190 (24) 157.92 ± 12.15 150–220 (24) 174.58 ± 20.21	Not observed 160–250 (12) 150–220 (14) 199.17 ± 25.03 187.14 ± 18.16 190–290 (12) 160–210 (14) 222.50 ± 27.01 190.71 ± 12.69		40–170 (12) 94.17 ± 37.77 140–250 (50) 176.00 ± 24.99 150–290 (50) 190.60 ± 27.80
	OoL	170–240 (11) 195.45 ± 24.23	240–290 (5) 268.00 ± 21.68	280–330 (3) 306.67 ± 25.17	170–330 (19) 232.11 ± 51.05
	OoW	200–240 (12) 219.17 ± 14.43	230–280 (5) 260.00 ± 24.60	200–260 (3) 226.67 ± 30.55	200–280 (20) 230.50 ± 24.60
	AvL	520–740 (23) 659.57 ± 54.89	660–1190 (12) 884.17 ± 169.46	720–860 (9) 768.89 ± 50.36	520–1190 (44) 743.18 ± 137.06
	RL	320–430 (23) 390.43 ± 31.11	340–680 (12) 527.50 ± 105.75	440–580 (9) 480.00 ± 43.87	320–680 (44) 446.14 ± 86.38
Avicularia	RW PrL PrW	110–190 (23) 143.04 ± 18.45 180–320 (24) 253.33 ± 31.30 170–250 (23) 212.17 ± 22.55	140–290 (12) 195.00 ± 44.21 270–550 (12) 361.25 ± 105.79 220–360 (12) 267.50 ± 42.88	130–180 (9) 151.11 ± 19.00 230–320 (10) 261.00 ± 26.01 210–280 (9) 232.22 ± 24.38	110–290 (44) 158.86 ± 35.39 180–550 (46) 283.15 ± 74.71 170–360 (44) 231.36 ± 37.45
	OpL	60–140 (14) 101.43 ± 29.58	90–220 (10) 140.00 ± 40.00	80–130 (8) 108.75 ± 15.53	60–220 (32) 115.31 ± 34.36
	OpW	70–130 (14) 91.43 ± 19.16	60–195 (10) 115.50 ± 48.79	90–120 (8) 102.50 ± 10.35	70–195 (32) 101.72 ± 31.28
Kenozooids	KzL KzW OpD	Not observed	290–740 (6) 500.00 ± 159.00 160–370 (6) 296.33 ± 83.80 60–120 (6) 85.00 ± 25.10	340–400 (4) 372.50 ± 27.54 360–400 (4) 377.50 ± 20.62 140–180 (4) 157.50 ± 17.08	290–740 (10) 449.00 ± 136.50 160–400 (10) 328.80 ± 76.16 60–180 (10) 114.00 ± 43.00