Oriocrassatella piauiensis, Anelli & Simões & González & Souza, 2012

Anelli, Luiz E., Simões, Marcello G., González, Carlos Roberto & Souza, Paulo A., 2012, A new Pennsylvanian Oriocrassatellinae from Brazil and the distribution of the genus Oriocrassatella in space and time, Geodiversitas 34 (3), pp. 489-504 : 498-500

Oriocrassatella piauiensis n. sp. (Fig. 4)

TYPE MATERIAL. — Holotype GP/1 T 2022 . — Paratypes GP/1 T 2023 , 2024 , 2026-2028 ; DNPM 148 , 219 , 220 , 221 a, 234, 271 .

ETYMOLOGY. — The specific epithet refers to Piauí State, northern Brazil, where the species was found.

TYPE HORIZON. — Mucambo dolostone, Piauí Formation, Parnaíba Basin.

AGE. — Bashkirian to Moscovian. The time-range assigned herein comprises the more reliable relative ages to the Piauí Formation, obtained from palynological data ( Dino & Playford 2002; Souza et al. 2010) and comparisons with the palynostratigraphical scheme erected to the neighbor Amazonas Basin ( Playford & Dino 2000).

MATERIAL EXAMINED. — Six internal molds of left valves and six of right valves; two external molds of left valves.

MEASUREMENTS. — See Table 1.

TYPE LOCALITY. — José de Freitas, (4°53’656’’S, 42°35’ 871’’W), Piauí, Brazil.

DIAGNOSIS. — Oriocrassatella with lateral teeth absent; non bifid cardinal tooth 2; ornamentation of regularly spaced lamellae with flattened surfaces showing rare bifurcation in anterior and posterior regions of shell.

DESCRIPTION

Internal and external molds up to 24 mm in length, and up to 17.5 mm in height. Shell thick based on internal molds, oval in shape, elongate, very compressed. Umbones depressed, beaks prosogy- rate slightly elevated above hinge. Umbonal carina weak and rounded, running from beaks to posterior ventral angle, defining a large respiratory margin. As seen in casts of external molds, anterior dorsal margin straight; anterior extremity convex; ventral margin slightly convex; posterior extremity slightly truncated; posterior dorsal margin straight. Ornamentation of concentric lamellae, regularly spaced, about two per millimeter, some showing bifurcating pattern anteriorly and posteriorly. Pedal or siphonal gapes absent. Lunule and escutcheon absent.

Hinge formula as follows:

Posterior RV /nsr – 3b – 3a/ Anterior LV /nsr 4b – 2 –/

Left anterior cardinal (2) strong, non arched or bifid; left posterior cardinal (4b) weak, laterally compressed, vertical, sometimes showing sigmoid shape. Right anterior cardinal (3a) well defined, separated from the anterior dorsal margin by shallow depression. Right posterior cardinal (3b) straight, vertical, slightly inflated in both extremities. Resilifer (r) in left valve placed behind posterior cardinal (4b), cover deck absent; septum (s) strong, well developed in both valves, originating immediately posterior to beak, bounding resilifer posteriorly; nymph (n) well-defined in posterior wall of septum, close to beak. Ligament furrow (lf) very narrow, located posterior to the septum. Lateral teeth absent.

Adductor muscles scars similar in size. Anterior scar positioned close to anterior dorsal angle, twice higher than long, with irregular shape at posterior

Fig. 4. — Oriocrassatella piauiensis n. sp., Mucambo limestone; A, holotype, internal mold of right valve, GP/1 T 2022 ; B, internal mold of left valve, DNPM 076 ; C, latex cast, internal mold of right valve, DNPM 234 ; D, latex cast, magnified hinge area, internal mold of right valve, same specimen; E, latex cast, internal mold of left valve, magnified hinge area, DNPM 221 b ; F, latex cast, internal mold of left valve, same specimen; G, internal mold of right valve, GP/1 T 2024 ; H, muscle scars based in specimen DNPM 076 ; I, latex cast, external mold of left valve, DNPM 220 ; J, internal mold of right valve, DNPM 234 . Abbreviations: aa, anterior adductor ; apr, anterior pedal retractor; lf, ligament furrow; n, nymphs; pa, posterior adductor; pl, pallial line; r, resilifer; s, septum; ue, umbonal elevator; 2, left anterior cardinal; 3a, right anterior cardinal; 3b, right posterior cardinal; 4a, left posterior cardinal. Scale bars: 0.5 cm.

margin. Anterior pedal retractor small, well marked, not fused but placed close to dorsal extremity of the adductor. Posterior adductor located above posterior dorsal angle, nearly circular in shape. Posterior pedal retractor apparently fused to dorsal end of posterior adductor. Pedal elevator scar well-marked, located at tip of beaks. Pallial line well defined, without sinus.