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Opalia apostolorum (Iredale, 1936)

Description: Shell tall and slender, apex blunt. Teleoconch up to 5 whorls; whole surface covered with intritacalx densely sculptured with microscopic pits in a square pattern. Protoconch very large, low, smooth, of only whorl. Teleoconch whorls weakly rounded, with strong rounded axial ribs. Ribs aligned from whorl to whorl, 11 on last whorl. Axial sculpture restricted to intritacalx sculpture. On last whorl, axial ribs develop into large nodules at middle of whorl and terminate as large nodules on a basal rib. Base sculpture restricted to that of intritacalx. Aperture elongate oval, with strong varix externally. Umbilicus closed. Colour fawn.

Size: Up to 7 mm in length.

Distribution: Known only from holotype and paratype, both dredged between Balls Head and Goat Island, Port Jackson, NSW.

Remarks: This species has a well-developed intritacalx, the chalky, pitted, upper shell layer found in the genus Opalia. Fig. 2 shows the paratype, with much of the intritacalx worn away, revealing the relatively smooth shell layer below.

Fig. 1: HOLOTYPE dredged between Balls Head and Goat Island, Port Jackson, NSW (C.007868) .

Fig. 2: Detail of intritacalx. PARATYPE dredged between Balls Head and Goat Island, Port Jackson, NSW (C.334096).

 


Copyright Des Beechey 2008