Serratocrista scaldisensis, Mottequin & Simon, 2017

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 : 21-24

Serratocrista scaldisensis sp. nov.

Figures 4 , 17-19 , Table 2

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Etymology. From Scaldis (Latin: Escaut), in reference to the Escaut river on the banks of which the town of Tournai is settled.

Holotype. RBINS a13110 ( Figures 17.12-16 , 18.1, 18.6 ).

Paratypes. RBINS: a13108 ( Figure 17.1-6 ), a13109 ( Figure 17.7 -11), a13111 ( Figures 17.17- 21, 18.2-3, 18.19-21 ), a13112 ( Figure 17.22-25 ), a13113 ( Figure 18.4-5 ), a13114 ( Figure 18.7-13 ), a13115 ( Figure 18.14-18 ), and a13116 ( Figure 19 ) . Additional material. RBINS: four articulated specimens.

Type locality. Tournai area (southwestern Belgium) ( Figures 2-3 ).

Type stratum. Tournai Formation, Tournaisian ( Figure 4 ).

Diagnosis. A small-sized (ca. 15 mm in width) Serratocrista species of, wider than long, planoconvex in profile and subquadrate-rounded in outline, with maximum width near midlength. Ornamentation multicostellate, 12 to15 costellae per 5 mm at anterior margin with costellae increasing essentially by intercalations. Dorsal muscle field impressed, obscure, poorly delimited anteriorly, extending up to 40 percent of the valve length; myophragm low.

Description. Shell small-sized (up to 15.6 mm in width), wider than long, subquadrate in outline, plano-convex; maximum width near midlength; hinge line shorter than maximal width; cardinal angles and anterior margin rounded; anterior commissure rectimarginate to slightly unisulcate. Shell extropunctate with extropunctae arranged radially along the axis of the costellae ( Figure 18.2-3 ).

Ventral valve convex, with maximum height near posterior margin, then decreasing progressively towards anterior commissure; umbo small but prominent, umbonal region sometimes deformed (flattened) by cementation with koskinoid perforations ( Figure 18.19-21 ), which are also present on the interarea); beak not curved; interarea triangular, low, cata-apsacline to apsacline, flat to slightly concave; pseudodeltidium strongly convex ( Figure 18.1-3 ).

Dorsal valve flat with, in some specimens, development of a shallow median depression; chilidium small, convex, medianly grooved; interarea linear, anacline, flat.

Ornamentation multicostellate (12–15 costellae per 5 mm at anterior margin) with costellae increasing essentially by intercalations, more rarely by bifurcations; ca. 10 concentric microlines per 1 mm, thickened at irregular interval (growth varices), and forming protuberances on rib crests ( Figure 18.6 ).

Ventral interior poorly known ( Figures 17.6 , 19.1-4 ); teeth small, rounded, unsupported; muscle field not observed.

Dorsal interior ( Figure 18.1-3 , 8 , 12-13 , 15-18 ) with cardinal process lobes small, posteriorly grooved; muscle field impressed, obscure, poorly delimited anteriorly, extending up to 40 percent of the valve length; myophragm low (observed in one specimen); socket ridges diverging from the hinge line at an angle of 26–48 degrees (n=2).

Dimensions ( Table 2)

Remarks. The ornamentation and the cardinalia of this limited material suggest an assignment to Serratocrista , although its type species is devoid of dorsal myophragm, which has been observed in ours. In their discussion of the original diagnosis given by Brunton (1968), Roberts (1971) and McIntosh (1974) reported the occasional occurrence of a dorsal myophragm in their material assigned to Brunton’s genus from Australia and Scotland, respectively. Besides the presence of a dorsal myophragm, the Belgian material is distinguished from Serratocrista fistulosa in its more flattened dorsal valve. Our specimens are markedly smaller than the Serpukhovian species Serratocrista dalriensis and S. cylindricosta , both described by McIntosh (1974). The Belgian species differs from S. truyolsi Martínez Chacón, 1979 from the Moscovian of Spain (see also Martínez Chacón, 2008) in its planoconvex shell and the not so deep dorsal median depression. The species from Tournai is relatively close to the Tournaisian ( China) and Visean ( Australia) Serratocrista sp. described by Sun and Baliński (2008) and Roberts (1971), respectively, but differs in its more divergent socket ridges.

Occurrence. Serratocrista scaldisensis is currently only known from the Tournai Formation in the Tournai area.

Figures

FIGURE 2. Schematic geological map of southern Belgium with location of the fossiliferous localities (modified from de Béthune, 1954). Abbreviations: D, Dréhance; F, Furfooz; G, Germany; HSMOTS, Haine-Sambre-Meuse Overturned Thrust Sheets; L, Grand Duchy of Luxemburg; N, The Netherlands; S, Sosoye.

FIGURE 3. Late Tournaisian sedimentation areas in the Namur-Dinant Basin (not palinspastically restored; modified from Hance et al., 2001; Poty et al., 2006; Poty, 2016) with location of the fossiliferous localities. Abbreviations: ASA, Avesnois sedimentation area; CSA, Condroz sedimentation area; D, Dréhance; DSA, Dinant sedimentation area; F, Furfooz; G, Germany; HSA, Hainaut sedimentation area; L, Grand Duchy of Luxemburg; N, The Netherlands; NSA, Namur sedimentation area; S, Sosoye; VSA, Visé–Maastricht sedimentation area.

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 8. Scatter diagrams of Leptagonia franca sp. nov. N: number of specimens measured. 1, Relation between shell width and length. 2, Relation between shell width and shell length/shell width ratio. 3, Relation beween shell width and thickness. 4, Relation between shell width and shell thickness/shell witdth ratio. 5, Relation between unrolled ventral valve length and ratio between unrolled ventral trail length (Vtl) and unrolled ventral disc length (Vdl). 6, Relation between unrolled dorsal valve length and ratio between unrolled dorsal trail length (Dtl) and unrolled dorsal disc length (Ddl).

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 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).