Piersaloceras gageli Teichert, 1930

Kröger, Björn, 2007, Concentrations of juvenile and small adult cephalopods in the Hirnantian cherts (Late Ordovician) of Porkuni, Estonia, Acta Palaeontologica Polonica 52 (3), pp. 591-608 : 601-602

Piersaloceras gageli Teichert, 1930

Figs. 4I, 7D.

1930 Piersaloceras gageli sp. nov.; Teichert 1930: 282, pl. 6: 9–10. Type locality: Piirsalu , north Estonia .

Type horizon: Pirgu Regional Stage, Late Ordovician.

Material.— Two specimens displaying juvenile–adult growth stages (TUG 1227/32, 38) .

Diagnosis.—Same as for genus, by monotypy.

Description.—Specimen TUG 1227/32 ( Figs. 4I, 7D) is a fragment of juvenile—adult growth stages with maximum lateral diameter of 15.2 mm, minimum diameter 6.5 mm, and length 38 mm. Deformed conch is dorso−ventrally crushed. Shell thickness is 0.3 mm at maximum diameter. Youngest septum is 10 mm adapical of adoral margin of fragmented adult body chamber, there lateral diameter is 13.8 mm. Distance to preceding septum is 1.8 mm. Septal spacing is 0.13 of cross section diameter. Septal crowding at youngest three septa. Septal distance is 1.4 mm at cross section diameter of 6.5 mm (0.2 of cross section diameter), where siphuncular diameter is 0.5 mm (0.08 mm of cross section diameter). Tubular, thin walled siphuncle that is clearly removed from shell wall. Septal necks are achoanitic. Surface is sculptured with 20 prominent longitudinal ribs around circumference and with numerous crenulated lirae. Lirae form forward bending saddles at position of ribs, approximately four lirae per one millimetre at lateral diameter of 15.2 mm. Lirae are thin adorally imbricated shell lamellae.

Specimen TUG 1227/38 is adult body chamber with cross section diameter of 18 mm. Adult peristome is slightly bulged outward. Growth axis is nearly straight.

Remarks.—The species represents the youngest record of the genus. However, Teichert (1930: 303) already mentioned that the stratigraphic range of Piersaloceras probably reaches toward the “Borkholm’sche Schicht”. Shell shape and ornamentation of Piersaloceras are very similar to Corbuloceras of the Bohemian Late Silurian. However, the spacing of the septa of the latter is wider, the siphuncular tube is thicker and slightly expanded within the chambers, and the siphuncle is closer to the venter in the latter.

Stratigraphic and geographic range.—Pirgu Regional Stage —Dolomitic limestones of the Siuge Member, Porkuni Regional Stage, Late Ordovician of north Estonia.