Clathrospira gondwanica, Ferrari & Bertero & Carrera, 2024

Clathrospira gondwanica View in CoL sp. nov.

Fig. 3J–N View Fig .

2020 Clathrospira subconica ( Hall, 1847) View in CoL ; Bertero 2020: 72, pl. 6: 7, 11, 12, 14; pl. 7: 1–5.

ZooBank LSID: urn:lsid:zoobank.org:act:.

Etymology: Referred to the first occurrence of Clathrospira in Gondwana (South America).

Type material: Holotype CEGH-UNC 24738 (11), complete and well preserved teleoconch without protoconch and juvenile whorls . Paratype CEGH-UNC 24737 , complete and well preserved teleoconch with juvenile whorls; from the type locality and horizon .

Type locality: Sierra de Villicum locality, San Juan Province, Argentina .

Type horizon: La Pola and Don Braulio formations, Sandbian–Hirnantian, Upper Ordovician, lower Palaeozoic.

Material.— Type material and 25 recrystallized teleoconchs ( CEGH-UNC 24739–24751 , 24753–24764 ) from type locality and horizon .

Diagnosis.—Shell conical, trochiform, anomphalous and coeloconical to cyrtoconical. The pleural angle is variable and ranges 60–100°. The peripheral selenizone is situated above mid-whorl. The selenizone is cord-like shaped on juvenile whorls and concave on mature whorls, and lunulae are opisthocyrt. The prosocline growth lines on the flank of whorls are visible above selenizone. The growth lines are prosocyrt to orthocline on base. The aperture is subquadrangular.

Description.—Trochiform, conical, anomphalous, medium-sized shell with a height of 40−95 mm and a width of 40−85 mm.The pleural angle is variable and ranges 60−100°. The teleoconch consists of six whorls; spire whorls are coeloconoidal and last whorl becomes slightly cyrtoconoidal ( Fig. 3K View Fig 2 View Fig ). The selenizone is peripheral and located slightly above mid-whorl; opisthocyrt lunulae are clearly visible ( Fig. 3J View Fig ). The selenizone has a cord-like shape on spire whorls and turns into slightly deep, concave and U-shaped on last whorl ( Fig. 3J View Fig ) and it is bordered by two acute spiral lirae. The ornament consists of strongly prosocline and fine growth lines on the flank of whorls above the selenizone; the growth lines are intercepted by weak and irregularly spaced spiral cords. On last whorl, below the selenizone and towards the base the growth lines become sligthly prosocyrt to orthocline. The base is convex and the aperture subquadrangular.

Remarks.—The species here described is very similar in shell shape and ornamentation to the type species Clathrospira subconica ( Hall, 1847) , but the Argentinean form shows neither the narrow umbilicus nor the fine spiral threads. Clathrospira glindmeyeri Rohr, 1996 (59, pl. 2: 11–17, 23; assigned by Ebbestad and Peel 2001 to the genus Semizona ), from the Whiterochian, Middle Ordovician of North America, differs from Clathrospira gondwanica sp. nov in having a more convex spire whorls with an cyrtoconoid shape, in having a narrow umbilicus, more acute prosocline growth lines, and a peripheral cord-shaped selenizone bordering the upper edge of last whorl. Deaechospira amouguerana ( Horný, 1997) (57, pl. 12: 7–13; pl. 13: 1–3, originally assigned to Clathrospira amouguerana ; Ebbestad et al. 2019: 261, figs. 17a–h, 18a–k, 19a–e), from the Sandbian–Katian, Upper Ordovician of Morocco, is very similar to Clathrospira gondwanica sp. nov., but differs in having a more arched whorls below the selenizone.

Stratigraphic and geographic range.—Sandbian–Hirnantian, Upper Ordovician, La Pola and Don Braulio formations, Sierra de Villicum and Quebrada de Don Braulio, San Juan Province, Argentina.