Gutiorthis incurvata Reyes−Abril and Villas, 2010

Reyes-Abril, Jaime, Villas, Enrique & Gutiérrez-Marco, Juan Carlos, 2010, Orthid brachiopods from the Middle Ordovician of the Central Iberian Zone, Spain, Acta Palaeontologica Polonica 55 (2), pp. 285-308 : 290-292

Gutiorthis incurvata Reyes−Abril and Villas sp. nov.

Fig. 4.

Etymology: For its posteriorly incurved vascula cardinalia and dentalia.

Type material: Holotype:MGM−5968−O, internal mould of ventral valve. Paratypes: twelve internal moulds and four external moulds of ventral valves, twelve external moulds and sixteen internal moulds of dorsal valves, and internal and external moulds of five ventral valves and three dorsal valves, with numbers: MGM−5946−O to MGM−5998−O.

Type locality: NE−IIA, 5600 m SE of Navas de Estena , Ciudad Real Province, Spain. UTM coordinates:lat 39 ° 27'32''N , long 4 ° 28'31''W.

Type horizon: About 110 metres above the base of the Navas de Estena Formation , Didymograptus artus Biozone , lower Oretanian , middle Darriwilian Stage of the Middle Ordovician Series .

Diagnosis.— Gutiorthis with rectangular to slightly acute cardinal angles at young stages, changing to obtuse with age; costate ribbing with high ribs of rounded cross section, nar−

Fig. 4. Orthid brachiopod Gutiorthis incurvata Reyes−Abril and Villas gen. et sp. nov. A. Holotype, MGM−5968−O, internal mould (A 1), latex cast of inte− H rior (A 2) and latex cast of exterior (A 3) of ventral valve. B. MGM−5946−O, internal mould (B 1) and latex cast of interior (B 2) of ventral valve.

C. MGM−5948−O, latex cast of exterior of ventral valve. D. MGM−5950−O, internal mould (D 1) and latex cast of interior (D 2) of ventral valve.

E. MGM−5996−O, latex cast of exterior of dorsal valve. F. MGM−5989−O, internal mould (F 1) and latex cast of interior (F 2) of dorsal valve.

G. MGM−5995−O, latex cast of exterior of dorsal valve. H. MGM−5984−O, internal mould (H 1) and latex cast of interior (H 2) of dorsal valve.

I. MGM−5973−O, latex cast of exterior of dorsal valve. Scale bars 5 mm.

doi:10.4202/app.2009.0032

rower than interspaces, numbering 17–22 at valve margin, including occasionally up to two costellae. Dorsal valve with high notothyrial platform; cardinal process flanked by two slender notothyrial ridges in adults.

Description.—Shell ventribiconvex, up to 26 mm long, with semicircular outline in young stages to suboval in adults. Maximum width along hinge line in young stages and along mid valve or posterior third of valve in adults; cardinal angles rectangular to slightly acute in young stages changing to obtuse in adults; 55–90% as long as wide, but part of that wide range due to deformation; hinge line 68–100% as wide as maximum valve width. Ventral valve strongly convex, weakly carinate, maximum depth at middle part of valve, 20–48% as deep as long (mean [m] = 34%, variance [v] = 1%, number [n] = 14); ventral interarea apsacline, slightly curved, 6–11% as long as valve (m = 8%, v = 0.2%, n = 11), with wide and open delthyrium. Dorsal valve weakly convex, 55–88% as long as wide (m = 69%, v = 1%, n = 29), slightly sulcate with up to 2 costae on sulcus; dorsal interarea planar, anacline, shorter than ventral interarea, with open notothyrium. Ornamentation costate, with high ribs of rounded section, narrower than intercostal spaces, numbering 17–22 at valve margin, 20 being the commonest number, including occasionally up to 2 costellae; with 6 ribs per 5 mm counted 5 mm anteromedially from umbo, about 3 capillae per 0.1 mm, well marked on ribs, and 4 fila per 0.1 mm well marked on intercostal spaces, as well as up to 4 conspicuous growth lines in largest valves.

Ventral interior with crural fosettes on massive, triangular teeth, supported by short dental plates, continuous anteriorly with short and incurved muscle bounding ridges; muscle field subtriangular, 24–43% as long as valve (m = 32%, v = 0.2%, n = 19), 21–35% as wide as valve (m = 25%, v = 0.1%, n = 24), with adductor scars 11–16% as wide as muscle field (m = 14%, v = 1%, n = 4), slightly shorter than diductor scars and not enclosed anteriorly; mantle canal system saccate, with vascula media parallel and adjacent, diverging at the anterior third of valve, and posterior distal branches incurving posterolaterally to intersect posterior valve margin, and oblique to ribbing.

Dorsal interior with high, prominent notothyrial platform in adult stages, continuous anteriorly with strong median ridge, reaching mid length of valve; cardinal process blade−like, high and thin, strengthened with age and flanked by slender notothyrial ridges; brachiophores rod−like, diverging at about 90 °, thickening and welding to notothyrial platform with age; dental sockets excavated on secondary shell deposits; muscle field quadripartite, 38–57% as long as valve (m = 47%, v = 0.3%, n = 9), 23–34% as wide as valve (m = 31%, v = 1%, n = 15), with larger anterior pair than posterior pair, separated by curved, transverse ridges, diverging anteriorly; mantle canal system with vascula media strongly impressed, diverging from anterior adductor scars, and distal posterior branches incurving posterolaterally.

Shell with internal margins of both valves crenulated, with deep grooves, corresponding to crest of ribs, and wide eminences with shallow sulci on intercostal spaces.

Discussion.—These shells display external features similar to those illustrated in the drawings of Orthis lusitanica Sharpe, 1849 , from the lower Oretanian of Valongo ( Portugal). However, a precise comparison with this species is not possible since its internal features were not described; moreover, the two external moulds on which the brief description of O. lusitanica is based, could not be found in Sharpe’s (1849) collection housed at NHM (Sarah Long, personal communication 2007). However, from a formal point of view, O. lusitanica is a valid taxon, since it was published including a description and figures. Nevertheless, since it is based on an incomplete sample, not allowing with certainty assignment of new specimens to the species, or allowing a precise generic attribution, it is proposed to restrict the species to the lectotype. For this purpose the lectotype is chosen herein as the external mould of a ventral valve, identified by Sharpe (1849: pl. 6: 5a) as a dorsal valve, where the costate ornamentation, pointed out by the author, can be observed. Regarding the second specimen assigned to O. lusitanica by Sharpe (1849: pl. 6: 5b), a dorsal valve, it is similar externally to those of Gutiorthis incurvata Reyes−Abril and Villas gen. et sp. nov. or even to Paralenorthis estenaensis Reyes−Abril and Villas sp. nov., although a precise comparison with them is again not possible, for the reasons stated above.

Stratigraphic and geographic range.—This species is known from both flanks of the Navas de Estena syncline (localities SP−II, south of San Pablo de los Montes, Toledo Province, and NE−IIA, southeast of Navas de Estena, Ciudad Real Province), in the lower part of the Navas de Estena Formation.