Looneyellopsis? sagittensis sp. nov.

Fig 5.2A–C

2022 Gen. et. sp. indet. 2.—Guzmán et al.: 17, Fig. 11.G–I.

Etymology: From the Latin “ sagitta ”, meaning arrow, in reference to the arrow-shaped outline of this species in dorsal view.

Material: 7 specimens.

Figured specimens: ULVG-14212

Dimensions:

Diagnosis: A species with a distinctive arrow-shaped outline in dorsal view, four lobes separated by three sulci, and coarse puncta of irregular size covering the carapace.

Description: Very small carapace of sub-rectangular outline in lateral view and arrow-shaped in dorsal view. Anterior margin rounded and slightly infracurvate, extending slightly along the ventral margin. Posterior truncated. Ventral margin slightly concave, dorsal margin straight.

LV overlaps the RV in the antero-dorsal margin. Greatest height in the anterior cardinal angle, greatest length just beneath mid-height, greatest width in the posterior third of the carapace.

Area-wide ornamentation (sensu Sames 2011) consists of coarse puncta of irregular size except on the dorsal and ventral margins. The puncta on the middle region of both valves are smaller and more densely concentrated than the ones in the anterior and posterior regions. Local ornamentation elements (sensu Sames 2011) consist of four lobes, separated by three sulci. One is located in the anterior region and extends from the dorsal margin to the ventral margin, two are located in the dorsal region, just anteriorly and posteriorly of the mid-length of the carapace, reaching from the dorsal margin to slightly above the mid-height, and the last is located on the posterior margin, extending from the postero-dorsal to the postero-ventral margin. There is also a strong intumescence in the posteroventrolateral region that extends, with diminishing expression, towards the antero-ventrolateral region, ending just short of the anterior margin lobe, which gives the species its characteristic arrow-like outline in dorsal view.

No sexual dimorphism was observed. Only adults were observed. No internal characteristics were seen as only tightly closed carapaces were recovered.

Remarks: Guzmán et al. (2022) identified this species for the Batateira Beds, classifying it as Gen. et. sp. indet. 2. Their specimens were slightly longer, at 0.32 mm instead of 0.26 mm; however, the height and width of the holotype described here are the same as their illustrated specimens, which suggests perhaps the presence of either sexual dimorphism or some degree of plasticity in the length of the carapace of this species. They argue against placing it in genus Looneyellopsis Kr ̂mmelbein & Weber, 1971 due to its broader posterior and less marked posterior cardinal angle in lateral view, and the presence of a sharply developed ventrolateral rib and three sulci on dorsal view instead of the nodules that Looneyellopsis possess. Some Looneyellopsis species do display comparably broad posterior margins in dorsal view, similarly to illustrated specimens here, such as L. multiornata Carignano and Cusminsky, 2015 and L. chinamuertensis (Musacchio, 1970). L. multiornata also displays local ornamentation elements in the form of coarse reticulation on its tubercles, similar to the way the coarse puncta cover the nodules in L.? sagittensis. However, Looneyellopsis? sagittensis does differ from other Looneyellopsis species in its size, being significantly smaller than all others, and due to the presence of lobes on its dorsal margin instead of tubercles or nodules. As this species has been identified in more than one study, and as it displays a very distinctive morphology and limited range that could hint at it being of biostratigraphic significance, the authors have opted to place it within genus Looneyellopsis with reservations, in the hopes of future studies better elucidating its taxonomic relationships.

Occurrences: 1PS-06-CE: AM-51 (12.6 m), AM-52 (7.2 m).

Stratigraphic and geographic distribution: Aptian, Crato Formation, Araripe Basin, Brazil (Guzmán et al. 2022; this study).