Schellwienella radialiformis Demanet, 1934

Mottequin, Bernard & Simon, Eric, 2017, New insights on Tournaisian-Visean (Carboniferous, Mississippian) athyridide, orthotetide, rhynchonellide, and strophomenide brachiopods from southern Belgium, Palaeontologia Electronica 37 (3), pp. 1-45 : 15-19

Schellwienella radialiformis Demanet, 1934

Figures 4 , 12-14

v* 1934 Schellwienella aspis mut. radialiformis nov. mut. Demanet, p. 85, pl. 7, figs. 6- 12.

v 1934 Schellwienella sp. ; Demanet, p. 81, text-fig. 15, pl. 7, fig. 3.

non 1954 Schellwienella (subgen. nov. Carlospina) radialiformis Demanet ; Reed, p. 183, pl. 3, fig. 21.

v 1958 Schellwienella aspis radialiformis Demanet ; Demanet, p. 126.

1969 Schellwienella aspis radialiformis Demanet ; Mortelmans, p. 31.

Type material. Demanet (1934) considered all the illustrated specimens as paratypes according to the legend of his plate 7. The articulated specimen RBINS a5930 ( Demanet, 1934, pl. 7, fig. 12; Figure 12.16-20 ) is selected here as the lectotype whereas the other RBINS specimens illustrated by Demanet (1934, pl. 7, figs. 6-11), namely a5924 ( Figures 12.1-5 , 13.11-12 ), a5925 ( Figure 13.14- 17 ), a5926 ( Figure 12.21-25 ), a5927 ( Figure 13.1- 5 ), a5928 ( Figures 12.6-10 , 13.13 ) and a5929 ( Figure 12.11-15 ), are considered as paralectotypes and fully illustrated herein.

Additional material. Two ventral and two dorsal valves, and ten articulated specimens.

Description. Shell large-sized (up to ca. 51 mm in width), wider than long, quadrate to subquadrate in outline, slightly mucronate, strongly dorsibiconvex to resupinate, widest at hinge (juveniles) or anteriorly to it (adults); anterior margin rounded; anterior commissure rectimarginate to slightly uniplicate.

Ventral valve posteriorly convex then becoming concave anteriorly (resupinate shell) or rarely slightly convex (dorsibiconvex shell); umbo small; interarea triangular, high, flat to slightly concave, catacline to anacline; pseudodeltidium convex and perideltidium flat ( Figure 13.11, 13.17 ); median depression rarely developed and occurring in anterior part of valve; koskinoid perforations developed in umbonal area ( Figure 13.12 ).

Dorsal valve convex with maximum height located at midvalve or posteriorly and then decreasing rapidly towards anterior commissure; posterolateral areas flattened in posterior view; interarea linear, flat, anacline; chilidium convex.

Ornamentation parvicostellate; in some specimens, costellae can thicken so much that they become as large as the costae at the anterior margin; at front, 7–11 costae and costellae per 5 mm; growth lamellae numerous irregularly spaced, more crowded near margins in adults; filae fine, forming minute ridges across the crests of the costae and costellae (ca. 14 per 1 mm) ( Figure 13.12- 13 ).

Ventral interior ( Figures 12.11 , 13.1, 13.15-17 ) with large and deep delthyrial cavity; lateral apical cavities not filled in; dental plates strongly divergent anteriorly (78–93 degrees [n=4]), enclosing the posterior half of the muscle field; teeth large; muscle field slightly impressed, flabellate, slightly wider than long, extending up to 38 percent of the valve length; adductor muscles bounded laterally by two very low slightly curved ridges (but not fusing) and divided by a slender and low myophragm not extending beyond the distal extremities of the lateral ridges; diductor field large, flabellate, entirely enclosing the adductor field and anteriorly limited by a low ridge.

Dorsal interior ( Figures 13.2, 13.20, 13.22-24, 14.3-4 ) with socket ridges divergent at 90 degrees (n=1!) from another and only slightly curved, fused to cardinal process lobes; sockets deep, round-bottomed and laterally bounded by valve floor; cardinal process lobes high, posteroventrally oriented, grooved posteriorly; muscle field longer than wide, extending up to 35 percent of the unrolled length of the valve; adductor scars oval, posteriorly defined by plates extending from socket ridges, and clearly separated by a median ridge.

Remarks. Demanet (1934) considered the specimens from Tournai as a mutation of Schellwienella aspis Smyth (1930) from the Tournaisian Hook Head Formation of southern Ireland (see Bassett and Bryant, 2006; Mottequin, 2010). According to the article 45.6.4 of the International Code of Zoological Nomenclature (1999), the epithet radialiformis has to be considered as of subspecific rank in Demanet’s (1934) publication. The species was promoted to a specific level by Reed (1954) and included in Schellwienella (Carlospina) Reed, 1954 , a subgenus considered as a synonym of Schellwienella by Williams (1965) and Williams and Brunton (2000). Schellwienella radialiformis Demanet, 1934 differs from S. radialis ( Phillips, 1836) , as revised by Brunton (1968), by its less strongly parvicostellate ornamentation (the primary costae are generally less pronounced), and its ventral muscle field has a markedly different outline (compare with Davidson 1861, pl. 25, fig. 17). Schellwienella radialiformis differs from S. aspis Smyth, 1930 by its parvicostellate ornamentation and its undulose to uniplicate anterior commissure. Demanet’s (1934) species is distinguished from S. cheuma Bassett and Bryant, 2006 notably in its parviclostellate ornamentation, its more convex pseudodeltidium, and its subrounded ventral muscle field.

Demanet (1934, text-fig. 15, pl. 7, fig. 3) illustrated the specimen RBINS a5921 that he considered as a ‘forme spéciale dérivant de Schellwienella ’ as it displays some structures observed on the ventral interarea which he interpreted as hinge denticles ( Figure 14.5 ). These structures, resulting from the intersection of the vertical and horizontal ornamentation of the ventral interarea, simply result from repetitive interruptions of the shell growth.

Occurrence. Schellwienella radialiformis is known from the Tournai Formation in the eponymous area.

Figures

FIGURE 4. Distribution of the athyridides, orthotetides and strophomenides described and/or discussed herein within the essentially carbonate Tournaisian and Visean succession of southern Belgium (see text). Stratigraphy, lithostratigraphy (incompletely represented here for the Hainaut and Visé–Maastricht sedimentation areas; formations and members are in roman and italic letters, respectively), and biostratigraphy are adapted from Poty et al. (2002, 2006, 2014). The lenticular Vignobles Member is not represented here as it is rarely developed (it is comprised between the Vaulx Member of the Tournai Formation and the Antoing Formation). Note that the “Grande Brèche” is an informal stratigraphic unit resulting from the dissolution of evaporitic levels in the Grands Malades Formation; other brecciated horizons occur in the Lives Formation.

FIGURE 12. Schellwienella radialiformis Demanet, 1934 from the Tournai area, Tournai Formation (Tournaisian). 1-5, RBINS a5924, articulated specimen, almost complete, in ventral, dorsal, lateral, posterior, and anterior views. 6-10, RBINS a5928, articulated specimen, almost complete, in ventral, dorsal, lateral, posterior, and anterior views. 11-15, RBINS a5929, articulated specimen, almost complete, in ventral, dorsal, lateral, posterior and anterior views. 16-20, RBINS a5930 (lectotype), articulated specimen, almost complete, in ventral, dorsal, lateral, posterior, and anterior views. 21-25, RBINS a5926, almost complete articulated specimen (with a microconchid attached to the ventral valve, close to the anterior margin) in ventral, dorsal, lateral, posterior, and anterior views. Scale bars equal 10 mm.

FIGURE 13. Schellwienella radialiformis Demanet, 1934 from the Tournai area, Tournai Formation (Tournaisian). 1-5, RBINS a5927, articulated specimen, almost complete, in ventral, dorsal, lateral, posterior and anterior views. 6-10, RBINS a13105, articulated specimen, almost complete, in ventral, dorsal, lateral, posterior, and anterior views. 11-12, RBINS a5924, detail (SEM) of the pseudodeltidium and of the koskinoid perforations penetrating in the umbonal part of the ventral valve. 13, RBINS a5928, detail of the microornament on dorsal valve (SEM). 14-17, RBINS a5925, incomplete ventral valve in external and internal views and detail (SEM) of the posterior internal and external morphology. 18-24, RBINS a13106, almost complete dorsal valve in dorsal, lateral, posterior, and internal views and detail (SEM) of the posterior morphology (cardinal process). Scale bars equal 10 mm (1-10, 14, 18-22), 1 mm (11), 0.25 mm (12), 0.5 mm (13), 2 mm (17, 23), 2.5 mm (24), 5 mm (15).

FIGURE 14. Schellwienella radialiformis Demanet, 1934 from the Tournai area, Tournai Formation (Tournaisian). 1-4, RBINS a13107, almost complete dorsal valve in dorsal, lateral and posterior views and detail of the chilidium and cardinal process lobes. 5-10, RBINS a5921, articulated internal mould with shelly remains in ventral, dorsal, lateral, posterior and anterior views and close-up of the ventral interarea (5). Scale bars equal 10 mm (1-2, 4-6), 1 mm (4, 5).

FIGURE 15. Schellwienella ornata Demanet, 1934 from Visé, Visé Formation (Visean, Warnantian). 1-8, RBINS a5922 (lectotype), articulated internal mould in ventral, enlarged ventral (showing the extent of the traces left by the dissolved dental plates), dorsal, lateral, posterior, and anterior views, and internal views of a latex cast (SEM) showing the internal morphology of the posterior part of the specimen (7-8). 9-14, RBINS a5923 (paralectotype), articulated specimen (partly sectioned, probably by Demanet) in ventral, dorsal, lateral, posterior, and anterior views, and close-up (SEM) of the parvicostellate ornamentation in the central part of the dorsal valve. Scale bars equal 10 mm (1, 3-6, 9-13), 5 mm (2), 2.5 mm (7-8), 1.25 mm (14).

FIGURE 16. Schellwienella cylindrica (M’Coy, 1844), from the Visean (Brigantian) of Castle Espie (Comber, Co. Down, Ireland). 1-3, NMING:F6267 (lectotype), almost complete dorsal valve in dorsal, lateral, and posterior views. Scale bar equals 10 mm.

FIGURE 17. Serratocrista scaldisensis sp. nov. from the Tournai area, Tournai Formation (Tournaisian) (all SEM). 1-6, RBINS a13108, articulated specimen, almost complete, in ventral, dorsal, lateral, posterior, and anterior views, and close-up of the umbo showing the absence of dental plates. 7-11, RBINS a13109, articulated specimen in ventral, dorsal, lateral, posterior, and anterior views. 12-16, RBINS 13110 (holotype), articulated specimen in ventral, dorsal, lateral, posterior, and anterior views. 17-21, RBINS a13111, articulated specimen in ventral, dorsal, lateral, posterior, and anterior views. 22-25, RBINS a13112, almost complete ventral valve in ventral, lateral, posterior, and anterior views. Scale bars equal 1 mm (6), 5 mm (1-5, 7-25).

FIGURE 18. Serratocrista scaldisensis sp. nov. from the Tournai area, Tournai Formation (Tournaisian). 1, 6, RBINS a13110 (holotype), close-up of the strongly convex pseudodeltidium, and detail of the microornament (central part of the dorsal valve). 2-3, 19-21, RBINS a13111, detail of the strongly convex pseudodeltidium and of the cardinal process, and close-up of the koskinoid perforations developed in the ventral umbonal area and on the interarea. 4-5, RBINS a13113, incomplete articulated specimen in dorsal view and close-up of the posteriorly grooved lobes of the cardinal process. 7-13, RBINS a13114, dorsal valve in external, internal and posterior (10) views, detail of the chilidium (9), the cardinal process (11), and oblique views of the internal posterior region (12-13). 14-18, RBINS a13115, almost complete dorsal valve in external, internal and posterior views and oblique views of the internal posterior region. Scale bars equal 1 mm (1-3, 5-6, 9, 11, and 19-20), 2.5 mm (4), 5 mm (7-8, 10, 14-16, 12-13, and 17-18), 0.1 mm (21).

FIGURE 19. Serratocrista scaldisensis sp. nov. from the Tournai area, Tournai Formation (Tournaisian). 1-4, RBINS a13116, articulated specimen, incomplete, in dorsal view (1) with detail of the extropunctae arranged radially along the axis of the costellae (2, 3), and of the basal part of the pseudodeltidium and of the teeth (4). Scale bars equal 2 mm (1), 0.5 mm (2), 0.025 mm (3), 1 mm (4).

FIGURE 20. Lamellosathyris lamellosa (Léveillé, 1835) from the Tournai area, Tournai Formation (Tournaisian). 1-5, RBINS a13119, juvenile articulated specimen in ventral, dorsal, lateral, posterior and anterior views. 6-10, RBINS a13120, articulated specimen in ventral, dorsal, lateral, posterior, and anterior views. 11-15, RBINS a5468, articulated specimen in ventral, dorsal, lateral, posterior, and anterior views. 16-20, RBINS a13121, articulated specimen in ventral, dorsal, lateral, posterior, and anterior views. 21-25, RBINS a13122, articulated specimen (with two microconchids attached to the right dorsal flank) in ventral, dorsal, lateral, posterior and anterior views. 26-30, RBINS a13123, articulated specimen in ventral, dorsal, lateral, posterior, and anterior views. Scale bars equal 10 mm.