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Discotectonica acutissima (G.B. Sowerby III, 1914)

Description: Shell very low spired, ratio of width to height about 2.5. Whorls flat or concave, last whorl sharply keeled. Whorls sculptured with 815 spiral threads, crossed by numerous fine growth lines. Umbilicus wide, about 30% of base diameter, margined with several corded ribs; remainder of base with fine spiral threads. Spire cream to grey, with indistinct irregular fawn axial streaks; base white to grey.

Size: Largest specimen seen measured 43 mm greatest diameter.

Distribution: Subtropical and tropical Western Pacific. In eastern Australia, known from only 3 specimens: Off Port Stephens, NSW, in 274 m; NE of Cape Moreton, Qld, in 115-124 m; East of Newcastle, NSW, in 293 m.

Habitat: In Australia, taken in 115293 m. Rare in NSW.

Comparison: The relative flatness, the sharp peripheral keel and the base sculpture distinguish this species from other members of the family. Low specimens of Solatisonax injussa resemble it in shape, but lack the strong corded ribs around the umbilicus.

Synonymy: Russetia dilaniatus Garrard, 1961 is a previously recognised synonym.

Remarks: A similar species, Discotectonica petasus (Tomlin, 1928), has been taken off Cape Moreton, Qld, and may occur in northern NSW. It is distinguished by stronger spiral ribbing and alternate brown and white markings on the peripheral keel.

Figs. 1-3: NE off Cape Moreton, Qld, in 115124 m (C.91657)

 

Copyright Des Beechey 2016