Nucleospira hannoniae, 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 : 30-33

Nucleospira hannoniae nom. nov.

Figures 4 , 25-27 , Table 4

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v 1887 Athyris globulina de Koninck , p. 78, pl. 19, figs. 42-46.

? 1893 Athyris globulina ; Dewalque, p. 74.

1989 Cleiothyridina globulina ( Koninck, 1887) ; Grunt, p. 84.

Etymology. From Hannonia (Latin: Hainaut), in reference to the Hainaut Province where the town of Tournai is located.

Type specimens. Same as those of Athyris globulina de Koninck, 1887 that are selected herein. The specimen RBINS a5465 ( de Koninck, 1887, pl. 19, figs. 42-45) is selected here as the lectotype ( Figure 25.11-15 ) whereas the specimen RBINS a5466 ( de Koninck, 1887, pl. 19, fig. 46) is a paralectotype ( Figure 25.6-10 ).

Additional material. RBINS: 13 articulated specimens; ULg.PA: 8 articulated specimens.

Description. Shell small-sized (up to 10 mm in width), biconvex, slightly wider than long, subcircular in outline; hinge line clearly shorter than maximum width; anterior margin rounded to very slightly emarginate; anterior commissure rectimarginate to slightly undulose.

Ventral valve with flanks moderately sloping towards lateral commissures; umbo small but prominent; beak curved, not in contact with dorsal umbo; interarea low, triangular, apsacline, concave; delthyrium large, open (no deltidial plates observed due to deficient preservation [?]); shallow median depression occasionally developed and originating inconspicuously near umbo; no tongue.

Dorsal valve highest posteriorly to midvalve then decreasing progressively towards anterior margin; flanks sloping gently to moderately towards lateral commissures; no fold.

Shell smooth with only some irregularly spaced and thickened growth lines; spines solid, densely crowded, long (rarely preserved) ( Figure 25.27 ).

Ventral interior poorly known ( Figure 26.1-2 ); teeth cyrtomatodont, small.

Dorsal interior unknown; only some whorls observed ( Figure 26.1 ).

Dimensions ( Figure 27 , Table 4). An insufficient number of specimens have been measured. The scatter diagrams just indicate that relations between width and length of the shell or between the width and the thickness of the shell seem not affected by a large variability. The length/width or thickness/width ratios seem stable during the growth.

Remarks. The presence of solid spines covering the shell surface and the apsacline ventral interarea are characteristic of the genus Nucleospira , but their internal morphology was not investigated. Athyris globulina Waagen, 1883 (now included in Cleiothyridina Buckman, 1906 ; see Angiolini, 1995) and A. globulina de Koninck, 1887 are primary homonyms as rightly stressed by Grunt (1989), who included the latter species in Cleiothyridina . De Koninck’s species is a junior primary homonym and must be renamed: Nucleospira hannoniae . The name-bearing type of Nucleospira hannoniae remains that of Athyris globulina de Koninck, 1887 (not Waagen, 1883) (see above).

There are few reports of the genus Nucleospira in the Mississippian of Western Europe ( Brunton, 1984; Mottequin et al., 2015); this is most probably related to the small size of its representatives. Several species were described in the Mississippian of North America (see Weller, 1914, and Carter and Carter, 1970), while Pennsylvanian representatives of the genus are very rare according to Carter and Poletaev (1998). Externally, N. hannoniae is very close to N. carlukensis (Davidson, 1859) but according to Brunton (1984), the anterior commissure of the latter is commonly weakly uniplicate due to the presence of a sulcus whereas, in our very restricted material, it is generally rectimarginate (sulcus generally absent). Only the observation of the internal morphology of the material from Tournai will permit to better discriminate (or otherwise) both species. N. hannoniae differs from N. barrisi White, 1860 by the absence of a tongue (rectimarginate vs. uniplicate anterior commissure). On the basis of its external features, Nucleospira hannoniae is close to N. obesa Rowley, 1900 but can be distinguished from the latter by its larger size and the usual absence of a ventral median depression.

Occurrence. Nucleospira hannoniae is presently known only from the Tournai Formation (at least in the Vaulx Member) of the Tournai area. Dewalque (1893) reported Athyris globulina de Koninck, 1887 (not Waagen, 1883) within the Ourthe Formation ( Figure 4 ), but the conspecificity with the species from Tournai has to be confirmed.

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 25. Nucleospira hannoniae nom. nov., from the Tournai area, Tournai Formation (Tournaisian). 1-5, RBINS a13134, articulated specimen, almost complete, in ventral, dorsal, lateral, posterior and anterior views. 6-10, RBINS a5466 (paralectotype), articulated specimen, almost complete, in ventral, dorsal, lateral, posterior,and anterior views. 11-15, RBINS a5465 (lectotype), articulated specimen in ventral, dorsal, lateral, posterior, and anterior views. 16-21, RBINS a13135, articulated specimen in ventral, dorsal, lateral, posterior, and anterior views, and close-up of the interarea, Lemay quarry, Vaulx Member. 22-27, RBINS a13136, articulated specimen in ventral, dorsal, lateral, posterior, and anterior views, and close-up of the solid spines (right flank of the dorsal valve). Scale bars equal 2 mm (1-20, 22-26), 1 mm (21), 0.2 mm (21, 27).

FIGURE 26. Nucleospira hannoniae nom. nov., from the Tournai area, Tournai Formation (Tournaisian). 1-2, RBINS a13137, distorted and incomplete specimen in dorsal view showing two whorls of the spiralium and detail of one of the cyrtomatodont teeth. 3-4, RBINS a13138, distorted articulated specimen in dorsal view displaying a circular drill hole and detail of the latter. 5, RBINS a13139, distorted articulated specimen with a circular drill hole in ventral view. Scale bars equal 2 mm (1, 3, 5), 0.5 mm (2, 4).

FIGURE 27. Scatter diagrams of Nucleospira hannoniae nom. nov. N: number of specimens measured. 1, Relation between shell width and length. 2, Relation between width and shell length/shell width ratio. 3, Relation beween shell width and thickness. 4, Relation between shell width and shell thickness/shell width ratio.