Iravadia (Iravadia) dolini, Lozouet, 2003

Lozouet, Pierre, 2003, A new species of Iravadia s. s. (Mollusca, Gastropoda, Iravadiidae) from the late Oligocene of the Aquitaine Basin (southern France). The earliest record of brackish-water Iravadiidae?, Geodiversitas 25 (2), pp. 237-242 : 239

Iravadia (Iravadia) dolini n. sp. ( Figs 2 ; 3 )

TYPE MATERIAL. — Holotype and one paratype, Muséum national d’Histoire naturelle de Paris, Département Systématique et Évolution.

TYPE LOCALITY AND HORIZON. — Both specimens are from Bélus (Tauziède), Landes, from a detritical layer with Turritella Lamarck, 1799 in the late Oligocene (Chattian). Marls with Miogypsinoides Yabe & Hanzawa, 1928 , calcareous nannofossil zone NP 25 ( Cahuzac et al. 1995).

ETYMOLOGY. — The species is dedicated to Cyrille Dolin.

MEASUREMENTS (HOLOTYPE). — Height 3 mm; max. width 1.6 mm.

DESCRIPTION (HOLOTYPE)

Small shell, relatively solid, ovate conic, nonumbiculate. Teleoconch consisting of more than 3.5 convex whorls with impressed sutures. Protoconch slightly flat on top, smooth, of about two convex whorls, the first whorl minute, terminating in sharp discontinuity. Teleoconch with strong spiral sculpture; three main cords on each spire whorl, six on last adult whorl; cords separated by large interspaces that are broader than each spiral cord; threads present in the interspaces, notably below the suture, where one spiral thread is slightly larger than the others; all spiral sculpture crossed by numerous axial threads. Last whorl occupying 64.6% of total shell height. Aperture oval with relatively thick peristome; outer lip with heavy, slightly prosocline varix.

DISCUSSION

This is the first species of Iravadia s.s. to be recorded from the Tertiary. Previously described Oligocene Iravadiidae ( Janssen 1978: Ceratia , Hyala ; Lozouet 1998, 1999: Pseudonoba , Nozeba Iredale, 1915 ) have smooth shells or are weakly sculptured and are strongly dissimilar. Since I. dolini n. sp. has strong spiral sculpture, it seems clear that it is related to Indo-West Pacific species of Iravadia : Iravadia s.s. and Iravadia (Fairbankia) . According to Ponder (1984), the species of Fairbankia have slender spires and are more weakly sculptured. Iravadia (Iravadia) comprises species with predominantly spiral sculpture, but species such as Iravadia quadrasi (Boettger, 1893) also have pronounced axial sculpture. The Recent species I. angulata (Laseron, 1956) from Australia, included with little doubt in Iravadia s.s. by Ponder (1984), is especially close to I. dolini n. sp. Shared characters between I. angulata and I. dolini n. sp. are the protoconchs (slightly flattened summit of the protoconch rather than the classic depressed planorbiform protoconch of the Iravadiidae ) and the sculpture of three primary spiral cords on the spire. Iravadia dolini n. sp. differs from I. angulata in its shorter spire and the smaller, more ovate aperture which is not angled.

Figures

FIG. 2. — Iravadia (Iravadia) dolini n. sp.; A, protoconch of the paratype; B, abapical view of shell whorl sculpture, paratype; C-E, holotype, height 3 mm; C, apertural view; D, E, line drawings of the right lateral and abapertural views. Scale bars: A, B, 100 µm.

FIG. 3. — Iravadia (Iravadia) dolini n. sp., holotype; A, apertural view; B, abapertural view; C, right lateral view, height 3 mm.