Macunhaella posteroaltis Almeida-Lima, Guzmán, Maia, Jesus & Piovesan, 2024, sp. nov.

Macunhaella posteroaltis sp. nov. (Fig. 4G–J; Fig. 5B) 2022 Gen. et. sp. indet. 3—Guzmán et al., p.16, fig. 9M–P. 2023 Gen et. sp. indet. 3—Guzmán et al., p. 27, fig. 7E–F. Zoobank-link: urn:lsid:zoobank.org:act: EF74575E-5FE5-4F14-9AA5-1D5E1B134DAA Holotype: LMA-00042, L: 0.62 mm, H: 0.32 mm, W: 0.19 mm. Material: Seven carapaces. Derivation of name: In reference to the highest region. Type locality: Top of the Barbalha Formation to the base of the Crato Formation, Santana Group, Araripe Basin, Ceará State, Brazil. Type horizon: Top of the Barbalha Formation to the base of the Crato Formation, Santana Group, Araripe Basin, Brazil. Outcrop samples 3BAr06c–e, (Batateira River). Stratigraphic and geographic distribution: Aptian, Crato Formation, Santana Group, Araripe Basin, Crato Municipality, Ceará State, Brazil (Guzmán et al. 2022, 2023; this study). Diagnosis: Sub-rectangular outline in lateral view and fusiform in dorsal view, without ornamentation. RV overlapping LV at the anteroventral and posterodorsal regions. Description: Carapace smooth and sub-rectangular in lateral view; fusiform in dorsal view. Ventral margin straight; dorsal margin straight and slightly sloping towards the anterior region; posterior margin rounded and equicurvated; anterior margin sub-rounded and truncated. RV larger than LV, subtly overlapping at the anteroventral and posterodorsal regions. Greater height at posterior cardinal angle, greater length at mid-height and greater width at the median region. Anterior and posterior cardinal angles obtuse. Sexual dimorphism and internal features not observed. Remarks: The Macunhaella posteroaltis sp. nov. shows a reverse overlap pattern, RV larger than LV. This type of overlap has already been observed in other species that also show a normal overlap pattern (VL larger than RV) and this behavior has been interpreted as ecophenotypic responses of individuals to environmental stress events (e.g. Bergue et al. 2011; Almeida-Lima et al. 2022). Although all the specimens recovered in the material analyzed have reversed valve overlap, this is not a reliable diagnostic feature for distinguishing species and should be observed with parsimony in future identifications, since Macunhaella posteroaltis could be showing this type of overlap in response to unidentified stress.