Carapacestheria taschi ( Vallati, 1986 ), 2020

Monferran, Mateo D., Gallego, Oscar F. & Cabaleri, Nora G., 2020, Fig. 5 in Paralbunea dayriti, Zoological Studies (Zool. Stud.) 59 (37), pp. 1-11 : 3-4

Carapacestheria taschi ( Vallati, 1986) comb. nov.

( Fig. 3 ) urn:lsid:zoobank.org:act:4740A6B2-B4D5-46F8-B337-679A535D0372

Cyzicus (Euestheria) sp. A Tasch (in Tasch and Volkheimer, 1970). pag. 5–8.

Cyzicus (Euestheria) taschi Vallati, 1986 . pag. 31–33.

Material: Holotype UNPSJB-PI 280, Paratypes: UNPSJB-PI 267, 281-86; MACN-Pi 4892; CTES-PZ 7.678, 81–84.

Geographic provenance: Chubut province ( Argentina), Las Chacritas Member, Cañadón Asfalto Formation, Middle Jurassic. Cañadón Lahuincó (‘Frenguelli site’) locality GPS: 43°30'57.2"S, 69°8'26.7"W.

Emended diagnosis: Carapace small to very large in size with a shape varying from elongated oval to round (elliptical); umbo marginal in submedial to anterior position; dorsal margin short to long, anterior and posterior margins slightly curved to sharply curved; growth bands ornamented with irregular reticulation (0.005–0.03 mm) in dorsal to median-ventral zone to anterior zone of the valve, and change to radial lirae about 50 per mm in posterior-median zone. Cross-bars between radial lirae rarely present. Measurements (mm): L = 1.5–7, H = 0.6–6, H/L = 0.4–0.9, l = 0.6–4.8, a = 0.18–1, b = 0.1–2, c = 0.1–1.8, d = 0.5–2.7, e = 0.8–4.

Description: The carapace is small to very large in size with an outline varying from elongated oval to round (elliptical). The dorsal margin is short in round forms and long in elongated oval forms. The umbo is small marginal (0.5 mm) and projects submedial to anterior position. The anterior margin is slightly curved to curved and the posterior margin is slightly curved (c/d = 0.03–0.08) in elongated oval forms and curved to sharply curved (c/d = 0.07–0.15) in round elliptical forms. Growth lines are smooth, from 25 to 85 in number. The growth bands ornamented with irregular reticulation in anterior, dorsal to median-ventral zone ( Fig. 3C–E ) and radial lirae near the ventral and posteromedian regions ( Fig. 3F–G ). The polygonal reticulation shows a diameter of the mesh of 0.005–0.03 mm. The transitional ornamentation changes laterally from the reticulation to the radial lirae in the same growth band near to posterior-median area ( Fig. 3G ). Radial lirae (50 per mm) are count with 0.004 –0.007 mm width and filling 20% of the carapace surface. The presence of cross-bars between radial lirae is rare ( Fig. 3G ).

Remarks: Carapacestheria taschi (Vallati) was defined originally by Tasch as Cyzicus (Euestheria) sp. A ( Tasch and Volkheimer 1970). Subsequently, Vallati (1986) analyzed this material and defined as Cyzicus (Euestheria) taschi with polygonal reticulation in growth bands that changed to radial ornamentation in ventral carapace zone. Later, Cyzicus (Euestheria) taschi was interpreted as an eosestheriid by Gallego (2010), as well as, Cyzicus (Euestheria) sp. 1 from the Manantial Pelado Formation ( Vallati 1986).

According to the new SEM images, several specimens including the holotype have well developed reticulate ornamentation changing laterally to radial lirae in the same growth band near to posterior-median area. Therefore, these features support transferring this species from genus Euestheria to the Family Eosestheriidae . Euestheria is easily distinguished from the eosestheriid spinicaudatans in having only a fine reticulation and lacking radial lirae on the growth bands. Furthermore, this ornamentation pattern incorporating both reticulate and radial ornamentation is diagnostic of Carapacestheria Shen, 1994 , a genus defined from the Early to Middle Jurassic of Antarctica. In Carapacestheria , the carapace is of small or moderate size, and the reticulation shows a mesh diameter of 0.02–0.036 mm and radial lirae about 40 per mm. Minute punctae occur within the reticulation and between the radial lirae. In addition, the presence of cross-bars between radial lirae is observed for Carapacestheria disgregaris in figure 2 of Shen (1994). These characteristics match the Las Chacritas specimens.

Another similar genus is Menucoestheria from Triassic of Argentina ( Gallego and Covacevich 1998) and Poland ( Olempska 2004, considered by Kozur and Weems 2010 that belong to the genus Gregoriusella ). It resembles Carapacestheria in the presence of the transitional ornamentation changing laterally from reticulation to radial lirae in the same middle growth bands. However, Menucoestheria is characterized by meshes with 0.01 to 0.05 mm in diameter and 30 to 80 radial lirae per millimeter without cross-bars. In Pseudograpta , Yanjiestheria , Abrestheria, Nothocarapacestheria and Eosestheria the change from reticulation on the dorsal region to radial lirae on the ventral region is in the same growth bands and ventrally, and also, the radial lirae ornamentation are thinner.

Figures

Fig. 3. Carapacestheria taschi (Vallati) from the Las Chacritas Member, Cañadón Asfalto Formation. General carapace morphology; (A) UNPSJB-PI 282 paratype oval valve; (B) UNPSJB-PI 283 oval valve; SEM micrographs: (C) Details of the ornamentation from anterior area; (D) Ornamentation from dorsal area; (E) Details of the mid-dorsal ornamentation; (F) Ornamentation from postero-ventral area; (G) details of the postero-dorsal ornamentation. cr, cross bars; r, reticulate; rl, radial lirae.