Leinzia similis ( Holdhaus, 1918 )

Simões, Marcello G., Guerrini, Vitor B., Matos, Suzana A. & Rohn, Rosemarie, 2020, Morphology and taxonomic position of the bizarre Permian pachydomid bivalve Leinzia from Western Gondwana, Acta Palaeontologica Polonica 65 (2), pp. 291-303 : 295-299

publication ID	https://doi.org/ 10.4202/app.00665.2019
publication LSID	lsid:zoobank.org:pub:0DD13146-8830-4815-86E3-90C7CB8E8EEC
persistent identifier	https://treatment.plazi.org/id/364587AB-A70C-0629-FCA1-8390FBACEB8E
treatment provided by	Felipe
scientific name	Leinzia similis ( Holdhaus, 1918 )
status

Treatment

Leinzia similis ( Holdhaus, 1918)

Figs. 3–6 View Fig View Fig View Fig View Fig .

1918 Solenomorpha similis sp. nov.; Holdhaus 1918: 6, pl. 1: 1–5. 1929 Cuspidaria similis Holdhaus, 1918 ; Reed 1929: 45, pl. 4: 1–5, 11? 1949 Leinzia similis Holdhaus, 1918 ; Mendes 1949: 14, pl. 1: 1–5. 1971 Leinzia similis Holdhaus, 1918 ; Runnegar and Newell 1971: 53,

pl. 24: D–G, J.

Diagnosis. —Posteriorly elongated (length to height ratio 2.22 to 4.16), compressed, and non-gaping shell. Anterior shell margin straight, with a well-defined rostrum. Hinge of the right valve with a large, anteriorly inclined, blunt triangular tooth beneath the umbo, and a corresponding socket in left valve; true lateral teeth absent. Shell ornamentation with regularly spaced comarginal rugae, also present in the rostrum, but absent in the posterior umbonal carina. Anterior adductor muscle scar small, reniform; anterior pedal retractor scars well defined and separated from anterior adductor; anterior pedal protractor scar attached to dorsal edge of anterior adductor scar. Other muscle scars and palial line unkown.

Measurements.—See Table 2 for Leinzia similis (sensu stricto) shell measurements.

Description.—Small (maximum observed length 36 mm), thin-shelled, compressed bivalve, equivalve, posteriorly elongate ( Figs. 3 View Fig , 5B View Fig 2 View Fig ), and with a well-defined rostrum ( Fig. 5B View Fig ). Dorsal and ventral margins are subparallel; posterior margin sligthly concave ( Figs. 3A 3 View Fig , D, 5B View Fig 2 View Fig ); cardinal margin straight in front of beak. Posterior carina well marked, running diagonally from beak to posterior-ventral shell margin ( Fig. 3 View Fig ). Umbones low, prosogyrous; lunule absent, escutcheon long, well-defined. Ligament probably opisthodetic, parivincular, external. Hinge of right valve with large, anteriorly inclined triangular blunt tooth beneath the umbo and a corresponding socket in left valve; true lateral teeth absent ( Fig. 4A View Fig 1 View Fig , A 2 View Fig , B). External valve ornamentation with regularly spaced comarginal rugae extending to the anterior prolongation but absent behind umbonal carina Figs. 3 View Fig , 5B View Fig ). Fine growth lines visible between the regularly spaced comarginal rugae ( Figs. 3A 3 View Fig , 5B View Fig 2 View Fig ). The rugae are also evident on inner shell surfaces. Small lamellose or spinose projections along posterior dorsal shell margin are apparently absent. Anterior adductor muscle scar small, reniform; anterior pedal retractor scars well defined, separated from anterior adductor; anterior pedal protractor scar attached to dorsal edge of anterior adductor scar ( Fig. 4A View Fig 3 View Fig , A 4 View Fig ). Other muscle scars and pallial line unkown.

Remarks.—The right valve hinge of Leinzia similis (sensu stricto) with its large, forwardly inclined triangular blunt tooth beneath the beak and corresponding socket in the left valve is similar to that of various Permian Pachydomidae bivalves. However, the gross morphology of the rostrate shell of Leinzia similis differs from all other known Pachydomidae . The general shape, hinge, and muscle scars of Anhembia Mezzalira, Mendes, and Maranhão, 1990 ( Fig. 7B View Fig ), the other rostrum-bearing Pachydomidae shell of the Passa Dois Group are distinct of Leinzia similis (see discussion in Mezzalira et al. 1990). The anterior muscle scars of Leinzia similis (sensu stricto) are also similar to those found in Pachydomidae (i.e., Cowperesia Mendes, 1952 , Pyramus Dana, 1847 , Astartilla Dana, 1847, Plesiocyprinella Holdhaus, 1918 ), as described in Runnegar (1965) and Runnegar and Newell (1971), for example. The hinge and external ornamentation of Leinzia similis resemble those of Cowperesia anceps ( Reed, 1935) and, in addition, both shells are also laterally compressed. However, the general shell shape of Leinzia similis (sensu stricto) is completely distinct from that of Cowperesia anceps . Yet, the shells of Cowperesia anceps have a small, well-defined palial sinus and siphonal gape, which are absent in Leinzia similis . The posteriorly elongated shells of Leinzia similis (sensu stricto) with a well-marked posterior carina resemble that of Holdhausiella elongata ( Holdhaus, 1918) . Notably, the cardinal margin of some shells of this species have an anterior prolongation, but not a well-defined rostrum ( Fig. 7A View Fig ; see also Runnegar and Newell 1971: 41, fig. 16j–h). Yet, the external ornamentation of Holdhausiella elongata has irregularly spaced growth lines ( Fig. 7A View Fig ), which are clearly different from the regularly spaced comarginal rugae in Leinzia similis . Yet, the hinge of Holdhausiella elongata is edentelous and therefore different from that of Leinzia similis .

Although the external ornamentation of shells of Huabiella compressa David, Simões, Anelli, Rohn, and Holzförster, 2011 , from the Permian Gai-As Formation, Huab Basin, Namibia, are similar to that of Leinzia similis (sensu stricto), small lamellose or spinose projections along the posterior dorsal margin are only recorded in the Namibian shells. Unfortunately, the anterior margin, hinge and muscle scars are still unknown in Huabiella compressa . Therefore, a more precise comparison between Leinzia and Huabiella is currently not feasible. Finally, the hinge and gross morphology of Terraia altissima and other Terraiinae Scarlato and Starobogatov, 1979 bivalves ( Terraia aequilateralis Mendes, 1952 , Terraia curvata [ Reed, 1929], Terraia bipleura [ Reed, 1929]) are completely distinct of Leinzia similis (sensu stricto) and, therefore, the comparison among them is groundless.

Stratigraphic and geographic range.—Middle part of the Guadalupian Serrinha Member of the Rio do Rasto Formation, Paraná State, southern Brazil (see Rohn 1994; Rohn and Rösler 2000).