Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 3i): GS12173, CH/f478, Red Bluff Tuff, neck of Taruwhenua Peninsula, Pitt Island, Waipawan (GNS)
Beu & Maxwell (1990): Chapter 6; p. 91; pl. 3 i.
Description: Small for genus (height 70 mm), ovate-trigonal, strongly inequilateral and oblique, little inflated. Anterior area narrow, lanceolate, strongly depressed. Posterior ear moderately large, triangular; anterior ear very small, not visible in external lateral view. Posterior and anterior margins long, straight, steeply sloping, merging smoothly with strongly convex ventral margin. Commarginal sculpture of fine growth lines and stronger growth ridges. Radial sculpture of narrow, low, rounded, wavy costae of uneven spacing over most of exterior, including ears and anterior area. Cardinal area narrow, triangular, resilifer narrowly triangular, strongly oblique, directed posteriorly.
Comparison: The new species is apparently most closely related to Acesta imitata (Waitakian, Waipara River) but is much smaller and less strongly inflated, and has stronger radial sculpture at a similar stage of growth. Only three nominal species of Acesta have been described from New Zealand A. imitata, which has narrow but definite radial costae over most if not all of the exterior; A. regia (Whaingaroan?, Seal Rock, Woodpecker Bay, Southwest Nelson) with definite radial costae near the anterior and posterior margins but only grooves medially; and A. levitesta (Waitakian, Milburn Quarry, Otago; widespread), which is almost smooth except for a few weak ribs or grooves near the margins. All are large (height 150-210 mm) and thin-shelled and are rarely collected in anything like a complete condition, so the range of variation and limits of these nominal species are poorly known. In New Zealand the genus is recorded fossil from Haumurian (Late Cretaceous) to Mangapanian, and Recent from the bathyal zone (see Beu 1973b, p. 315-316 for occurrences). Marshall (2001) described Acesta maui and A. saginata from deep water around New Zealand and (A. saginata) the Southwest Pacific. A. maui is similar to A. levitesta, although much smaller, whereas A. saginata has coarser radial riblets and a wider shape, and more nearly resembles the Chatham Islands Eocene species. Most overseas records of the genus are bathyal but one extant species is recorded as shallow as 29 m (Vokes 1963). New Zealand fossil occurrences are mainly from limestone, marl and greensand inferred to have been deposited in moderately deep, offshore waters.
Distribution: Waipawan, Red Bluff Tuff, Tarawhenua Peninsula, Pitt Island, Chatham Islands (rare).
Cite this publication as: "A.G. Beu and J.I. Raine (2009). Revised
descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990). GNS
Science miscellaneous series no. 27."
© GNS Science, 2009
(Included with a PDF facsimile file copy of New Zealand Geological Survey Paleontological Bulletin 58 in CD version from: Publications Officer, GNS Science, P.O. Box 30368 Lower Hutt, New Zealand)