Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 48h): Te Piki, Cape Runaway, Haweran (oxygen isotope stage 7) (GNS, from a private collection)
Beu & Maxwell (1990): Chapter 16; p. 360; pl. 48 h.
Synonymy: Agnewia kempae Powell 1934, p. 273
Classification: Muricidae: Rapaninae
Description: Small for family (18-21 mm high), moderately elongate, with spire about equal in height to aperture and canal; whorls evenly and rather strongly convex, apart from a shallowly concave sutural ramp that is weak on early spire whorls and becomes more prominent on last whorl. Anterior canal short, straight, widely open, bordered by low, rounded fasciole with central hollow filled by smooth, thick area of inner lip. External sculpture of low, rounded, weak, indistinct axial folds, on most specimens fading out before last whorl, crossed by about 5 low, rounded, narrow, widely spaced spiral cords per whorl, with many more on sides and base of last whorl; whole surface crossed by many narrow, well raised, prominent, finely scaly spiral threads, about 5-6 on crests of each spiral cord where cords are present, but only threads remaining on last whorl of most specimens; a single low, rounded, basal cord on all specimens is generated by a protruding nodule near base of outer lip. Aperture smooth, simple. Protoconch large, conical, of 4 whorls, with a weak median keel and many short, anastomosing axial ridgelets and a terminal "Sinusigera claw", as in the living A. tritoniformis (Blainville).
Comparison: Agnewia kempae differs consistently from the living A. tritoniformis in having weaker axial folds, fading out before the last whorl (whereas they are consistently present on the last whorl in A. tritoniformis) and narrower, more widely spaced spiral cords. It therefore prominently reveals the raised basal spiral cord, generated by a nodule at the outer lip that is not present in A. tritoniformis. The Te Piki fossils consistently are buff-brown in colour and the living specimens have a translucent yellowish buff exterior, suggesting that an outer calcitic layer is present in both species. A. tritoniformis is common in the intertidal zone in New South Wales but is less commonly taken by SCUBA divers in a few metres in Victoria and in northern New Zealand (notably at Cape Karikari), always in very exposed rocky situations; rarely found as far south as East Cape to Tokomaru Bay. The presence of Agnewia at Te Piki is therefore further convincing evidence for a warm climate at the time of deposition. It presumably also implies that Agnewia dispersed from eastern Australia to New Zealand briefly during oxygen isotope stage 7 or earlier (in an interglacial period) but became genetically isolated, and so evolved into a distinct species. The occurrence of A. tritoniformis in stage 7 deposits at Hokianga Harbour, Northland (Beu, 2009) and living in New Zealand at present presumably results from later dispersal of planktotrophic larvae from eastern Australia, perhaps implying that these are pseudopopulations rather than breeding populations.
Distribution: Haweran; Te Piki, near East Cape, Haweran (oxygen isotope stage 7, 220 000 years B.P.) (type, and only locality), moderately common (about 10 specimens seen) in siltstone with a mixed semiestuarine to inner shelf faunule.
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)