Rhagasostoma Koschinsky, 1885

Taylor, Paul D., Martha, Silviu O. & Gordon, Dennis P., 2018, Synopsis of ‘ onychocellid’ cheilostome bryozoan genera, Journal of Natural History (J. Nat. Hist.) 52 (25 - 26), pp. 1657-1721 : 1698-1700

Genus Rhagasostoma Koschinsky, 1885

( Figure 26 )

Type species

Rhagasostoma hexagonum, Koschinsky, 1885 , by subsequent designation ( Canu and Bassler 1917, p. 31). Eocene, Lutetian, Gosaumergel von Götzreuth (= Gerhartsreiter Schichten), graben near Siegsdorf-Gerhartsreit, Traunstein, Bavaria, Germany. The type species of Rhagasostoma was given by Canu (1900, p. 428) as Semieschara dutempleana d’ Orbigny, 1852 , when assigning numerous Cretaceous species to this genus; however, this is invalid as d’ Orbigny’ s species was not listed by Koschinsky (1885) when he proposed the genus. The type species was corrected by Canu and Bassler (1917) to Rhagasostoma hexagonum Koschinsky, 1885 .

Diagnosis

Colony erect, vincularian ( Figure 26 (a,e,g)), dichotomously branched. Autozooids subhexagonal; zooidal boundaries raised ( Figure 26 (b)). Cryptocyst extensive, granular. Gymnocyst lacking. Opesia terminal, occupying about one-third of the frontal surface, longitudinally elliptical, with deep opesiular indentations at the proximolateral corners and an occlusor lamina ( Figure 26 (c,f)). Ovicells not observed. Avicularia vicarious, about the same size as autozooids, asymmetrical, observed only at branch bifurcations ( Figure 26 (d)); opesia longitudinally elliptical, located centrally.

Remarks

Rhagasostoma was introduced by Koschinsky (1885) in a little-known publication on the cheilostome fauna from the Cenozoic of Bavaria, an emended version of his PhD thesis that he had submitted in 1881 to the University of Munich. Koschinsky (1885) assigned three new species to his genus – R. hexagonum ( Figure 26 (a–g), R. circumvallatum ( Figure 26 (h,i)) and R. cingens – but offered no comparisons with existing genera, including Onychocella Jullien, 1882 ; which many subsequent authors (e.g. Waters 1891; Gordon and Taylor 1999) have interpreted as a senior synonym of Rhagasostoma . Others have maintained Rhagasostoma as a distinct genus for onychocellids with well-defined opesiular indentations and hyperstomial ovicells (e.g. Brydone 1930), some even placing it in a different family ( Aspidostomatidae ) from Onychocella ( Canu and Bassler 1920; Voigt 1930; Bassler 1953; Prud’ Homme 1968). However, later authors (e.g. Voigt and Williams 1973, p. 168) noted that a distinction between species lacking opesiular indentations and with endozooidal ovicells (‘ Onychocella ’) and species with opesiular indentations and hyperstomial ovicells (‘ Rhagasostoma ’) is difficult to make as there are many intermediate stages. Therefore, they disfavoured the use of Rhagasostoma as a valid genus name. Others have continued to use Rhagasostoma (e.g. Prud’ Homme 1968; Dzik 1975; El Safori and El Sorogy 1999).

Attempts to locate Koschinsky’ s collection have been unsuccessful, despite enquiries to Martin Nose (Bayerische Staatssammlung für Paläontologie und Geologie in Munich, Germany) and Kamil Zágoršek (Technická univerzita v Liberci, Lieberec, Czech Republic; formerly of the Narodni Museum, Prague). Therefore – and in view of the taxonomic importance of Rhagasostoma – we take this opportunity to designate a neotype for the type species, Rhagasostoma hexagonum Koschinsky, 1885 , SMF 29757 in the Voigt Collection, Frankfurt (SNG) ( Figure 26 (a–d)). This neotype and further material are from the Lutetian of the Rollgraben near Teisendorf, Bavaria, Germany, a locality c. 15 km north-east of the original type locality.

Range

Cretaceous–?Miocene.

Figures

Figure 26. (a–g) Rhagasostoma hexagonum Koschinsky; Eocene, Lutetian, Rollgraben near Teisendorf, Bavaria, Germany (a–d) neotype (designated here), SMF 29757; (a) bifurcating branch; (b) autozooid; (c) autozooid opesia with occulusor lamina;(d) avicularium;(e,f) SMF 29754;(e) branch; (f) autozooid opesia; (g) SMF 29755; branch. (h,i) Rhagasostoma circumvallatum Koschinsky; same provenance details as for (a–g); (h) SMF 32077b, autozooids with distinct occlusor laminae; (i) SMF 31915a, autozooids and avicularium. Scale bars: a, e, g = 500 µm; b, d, h = 200 µm; c, f, i = 100 µm.