Rhagasostoma aralense, 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 : 25-28

Rhagasostoma aralense sp. nov.

urn:lsid:zoobank.org:act:BA58BA06-3D7D-4C8C-8125-3490AE0A37E7

Fig. 10 , Table 5

Onychocella inelegans ( Lonsdale, 1850) – Favorskaya 1992: 125, pl. 64, fig. 6, pl. 65, fig. 1.

non Onychocella inelegans – Favorskaya 1992: 125, pl. 64, fig. 7.

Diagnosis

Colonies erect, bifoliate. Autozooids subrectangular; gymnocyst lacking; cryptocyst extensive with proximolateral peripheral caverns; opesiae terminal, semielliptical without shelf in the distal part, proximal edge crenulated with small, roundish opesiules; ovicells endozooidal. Avicularia interzooidal, larger than autozooids; rostrum channeled with pointed top, conical in outline, almost symmetrical; proximal part rounded, shorter and wider than rostrum; opesia egg-shaped with thin articular ridges bearing two short teeth proximally and an opesiular indentation between the teeth; opesiules lacking. Kenozooids at the margins of a colony, roundish, with small opesia.

Etymology

The species is named after its type locality, the region south of the former Aral Sea in the Republic of Karakalpakstan, Uzbekistan.

Material studied

Holotype

UZBEKISTAN • Republic of Karakalpakstan; early Campanian ( Cibicidoides temirensis / Bolivinoides decoratus decoratus Zone ; LS 13) of the southern Aral Sea Region ; TsNIGR Museum 26/12582 ( Fig. 10 A–F; figured by Favorskaya 1992: pl. 64, fig. 6).

Paratypes

UZBEKISTAN • Same data as for holotype; middle Campanian ( Brotzenella monterelensis Zone ; LS14) of the southern Aral Sea Region; TsNIGR Museum 28/12582 ( Fig. 10G ; figured by Favorskaya 1992: pl. 65, fig. 1).

Type locality and horizon

Uzbekistan, Republic of Karakalpakstan; southern Aral Sea Region; Cibicidoides temirensis / Bolivinoides decoratus decoratus Zone ( LS 13), early Campanian.

Description

Colony erect, flattened, bifoliate, fragments 3.0–5.0 mm long by 2.0–3.0 mm wide. Ancestrula and early astogeny not observed. Autozooids variable in shape, often broad and subrectangular with rounded distal ends; zooidal boundaries raised. Gymnocyst lacking. Cryptocyst extensive, finely pustulose, convex centrally, slightly depressed around edges, with proximolateral peripheral caverns; lateral wall of some caverns ribbed ( Fig. 10B , E–G). Opesia terminal, semielliptical without 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. 10C, F ). Proximal edge of opesia straight, crenulated, 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 infilling the opesiae). Septula not observed. Ovicells endozooidal, ooecium is formed by the distal zooid, seen as a low swelling of its proximal cryptocyst ( Fig. 10G ). Avicularia interzooidal, larger than autozooids, elongate. Rostrum channeled with elevated wing-like walls and a pointed tip, conical in outline, almost symmetrical. Proximal part rounded, shorter and wider than rostrum. Cryptocyst pustulose, concave, without peripheral caverns. Opesia egg-shaped with the narrow end pointing upwards and with thin articular ridges bearing two short teeth proximally and a short or long, slit-like opesiular indentation between the teeth; opesiules lacking. Kenozooids rounded, located at the margins of a colony. Cryptocyst finely pustulose. Opesia roundish, very small. Closure plates, intramural reparative budding of autozooids, avicularia and kenozooids not observed.

Remarks

Rhagasostoma aralense sp. nov. differs from R. brydonei sp. nov., R. minuens and R. operculatum sp. nov. in having avicularian rostra that are a conical in outline rather than spade-shaped or falciform. The new species differs from R. inelegans and R. angliae , which also have avicularian rostra conical in outline, in the rostrum being almost symmetrical and the avicularian opesia egg-shaped. The crenulated proximal edge of the autozooidal opesia is clearly another important character distinguishing this species from others. However, it is possible that the ribs are sediment particles or diagenetic crystals.

Distribution

Early to middle Campanian Uzbekistan: between Chimboy/Shımbay (Чимбой/Шымбай) and the Aral Sea in the Republic of Karakalpakstan.

Figures

Fig. 10. Rhagasostoma aralense sp. nov., southern Aral Sea Region, Uzbekistan. A–F. Holotype, TsNIGR Museum 26/12582, early Campanian, Cibicidoides temirensis/Bolivinoides decoratus decoratus Zone. A. Overview of erect bifoliate colony. B. Autozooids with proximolateral peripheral caverns and avicularia. C. Opesia of non-ovicellate autozooid with crenulated proximal edge. D. Edge of the colony with autozooids, avicularia, and kenozooids. E. Non-ovicellate autozooids with proximal peripheral caverns and avicularium. F. Non-ovicellate autozooids and avicularia. G. Paratype, TsNIGR Museum 28/12582, middle Campanian, Brotzenella monterelensis Zone, ovicellate autozooid and avicularium. Scale bars: A = 1 mm; B = 500 µm; C = 100 µm; D–G = 200 µm.

Tables

Table 5. Summary of measurements of Rhagasostoma aralense 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		North Ust-Yurt–Aral Basin Early to middle Campanian Southern Aral Sea Region
	AzL	330–650 (12) 430.00 ± 90.45
	AzW	230–300 (12) 259.17 ± 23.53
Autozooids	CvL OpL OpW	30–220 (12) 67.50 ± 52.25 90–160 (12) 117.50 ± 19.60 130–200 (12) 165.83 ± 22.75
	OoL	110–140 (2) 125.00 ± 21.21
	OoW	210 (2) 210.00
	AvL	470–880 (10) 674.00 ± 133.93
	RL	370–590 (10) 463.00 ± 73.34
Avicularia	RW PrL PrW	70–140 (10) 107.00 ± 25.84 100–300 (10) 211.00 ± 72.95 140–230 (10) 189.00 ± 26.44
	OpL	110–180 (9) 137.78 ± 26.35
	OpW	90–140 (9) 117.78 ± 17.16
Kenozooids	KzL KzW OpD	180–250 (2) 215.00 ± 49.50 130–150 (2) 140.00 ± 14.14 20–30 (2) 25.00 ± 7.07