Volgia deftera, Ernst & Wyse Jackson & Aretz, 2015

Ernst, Andrej, Wyse Jackson, Patrick N. & Aretz, Markus, 2015, Bryozoan fauna from the Mississippian (Visean) of Roque Redonde (Montagne Noire, southern France), Geodiversitas 37 (2), pp. 151-213 : 162-166

Volgia deftera n. sp.

( Figs 11 B-F; 12A-F; Appendix)

Evactinopora sp. – Ernst 2005: 51, fig. 1C-E, G. ETYMOLOGY. — The species name refers to the being the second known species of the genus (from Greek “ defteros ” – the second).

HOLOTYPE. — SMF 21.802 .

PARATYPES. — SMF 21.803- SMF 21.814.

TYPE LOCALITY. — Roque Redonde (Montagne Noire, southern France).

TYPE HORIZON. — Carboniferous, Mississippian (upper Visean).

DIAGNOSIS. — Crucifix-shaped colonies with relatively thick branches; mesotheca with median tubuli and longitudinal ridges parallel to growth direction; thin complete diaphragms occasionally present; hemisepta absent; lunaria weakly developed, irregularly horseshoeshaped; vesicles moderately large, polygonal in tangential section, with rounded roofs, arranged in 1-2 rows between autozooecia, 10-12 surrounding each autozooecial aperture; stereom thick, consisting of laminated material, completely separating autozooecia in exozone, containing abundant tubules; metazooecia (? exozonal tubes) locally abundant, flask-shaped, restricted to stereom; maculae lacking.

DESCRIPTION Colony consisting of erect bifoliate lobes, with secondary branches diverging at right angles in crucifix-shaped pattern. Branches 3.30-3.35 mm wide and 1.44-2.10 mm thick. Mesotheca 0.010 -0.015 mm thick, with a dark and thin middle layer and two light and thick outer layers, containing median tubuli and longitudinal ridges parallel to growth direction. Median tubuli 0.015 -0.020 mm in diameter consisting of hyaline calcite, rounded in transverse section, developing short and densely spaced lateral projections ( Fig. 12A, B ). Autozooecia recumbent on the mesotheca or epitheca for a relatively long distance, then bending upwards abruptly, intersecting the surface almost perpendicularly. Thin, complete diaphragms in autozooecia occasionally present. Autozooecial apertures circular to oval. Lunaria weakly developed, irregularly horseshoe-shaped.Vesicular skeleton well developed, covered in exozone by thick stereom. Vesicles moderately large, polygonal in tangential section, with rounded roofs, arranged in 1-2 rows between autozooecia, 10-12 surrounding each autozooecial aperture. Stereom thick, consisting of laminated material, completely separating autozooecia in exozone, containing abundant tubules. Tubules 0.010 -0.015 mm in diameter, with hyaline cores and narrow laminated sheaths. Indistinct maculae consisting of stereom and metazooecia (exozonal tubes) present. Metazooecia (? exozonal tubes) locally abundant, flask-shaped, restricted to stereom.

COMPARISON

The new species differs from Volgia arborescens ( Stuckenberg, 1895) by larger autozooecial apertures (0.17-0.29 mm vs 0.14-0.15 mm in Volgia arborescens ). Furthermore, no heterozooecia were reported in V. arborescens . Evactionopora sp. ( Ernst 2005: 51) from the Mississippian (Visean) of Sauerland ( Germany) is placed in the new species. It possesses five rays instead of four. However, that is a result of the bifurcation of one ray. Otherwise, it shows typical crucifix pattern ( Ernst 2005, Fig. 1C ). That specimen has branches of 4.2-4.6 mm width and 1.5-1.6 mm thickness.

Figures

FIG. 11. — A, Eridopora suarezi n. sp., tangential section showing autozooecial aperture,holotype SMF 21.794: B-F. Volgia deftera n. sp.; B, transverse section of the colony, holotype SMF 21.802; C, transverse section of the colony, paratype SMF 21.812; D, longitudinal section, paratype SMF 21.811; E, F, branch transverse section, paratype SMF 21.805. Scale bars: A, 0.2 mm; B-D, 2 mm; E, 1 mm; F, 0.5 mm.

FIG. 12.— A-F, Volgia deftera n. sp.; A, B, branch transverse section showing mesotheca with median tubuli (arrow),paratype SMF 21.805; C, longitudinal section, paratype SMF 21.804; D, tangential section showing autozooecial apertures, metazooecia (? exozonal tubes) and tubules, paratype SMF 21.810; E, longitudinal section showing external skeleton with metazooecia and tubules (arrow), SMF 21.810; F, tangential section showing autozooecial apertures and tubules (arrow), paratype SMF 21.809. Scale bars: A, B, F, 0.2 mm; C-E 0;5 mm.

FIG. 1. — A, Localisation of the Roque Redonde outcrop on a geological map showing the numerous limestone olistoliths (black) incorporated in the siliciclastic flysch deposits of the Laurens Flysch Group (grey) in the vicinity of Vailhan (modified from Engel et al. 1981); B, view on the Roque de Redonde from the NW. Abbreviation: RR, Roque Redonde.