Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 47g): holotype of S. delli murdochi, GS4055, R22/f6386, Upper Kai-Iwi Siltstone, Castlecliff, Wanganui, Castlecliffian (TM1656, GNS)
Beu & Maxwell (1990): Chapter 16; p. 350; pl. 47 g.
Synonymy: Turritella (Eglisia) symmetrica Hutton 1873a, p. 30; Zeacolpus (Stiracolpus) delli murdochi Marwick 1957b, p. 32; Beu & Maxwell 1990, p. 350, pl. 47g; probably = Z. delli Marwick 1957b, p. 31; Z. delli granti Marwick 1957b, p. 33; Z. shepherdi Marwick 1957b, p. 44; Z. delli vellai Marwick 1957b, p. 33; probably also several other synonyms.
Type species (as Turritella symmetrica) of Stiracolpus Finlay, 1926
Description: Small for family (20-25 mm high), tall and narrow, with only weakly convex whorls, flat base, and marked peribasal angulation on last whorl. Sculpture greatly dominated by 3 prominent, wide, widely spaced spiral cords of rounded cross-section (cords A, B and C); secondary and tertiary threads weak; no axial sculpture other than growth lines. On early spire whorls, cord B begins first, and A and C are weak; A and C strengthen after fifth whorl, and rival B on last 7-8 whorls. Outer lip thin, with wide, relatively shallow, V-shaped sinus with medial apex. Protoconch of about 1 smooth whorl, with large, rounded apex.
Comparison: The taxonomy of Stiracolpus is poorly understood. Beu (2009) made a preliminary attempt at reducing the species to 4-5 more realistic ones, but the comprehension of real species in this genus must await a molecular phylogenetic study, which has proved difficult to undertake because of the scarcity of living material in the Recent fauna. Many of Marwick's (1957b) nominal species and subspecies appear to be part of the variation of more widespread, more long-lived species (see particularly Marwick's table 2, where many Castlecliff intergrades are identified as "hybrids"). The many Castlecliff forms are particularly in need of revision; we illustrate a specimen identified by Marwick (1957b) S. delli murdochi as an example of the abundant Castlecliffian strongly tricostate type of shell, differing from the Recent, southern, coldwater S. symmetricus only in its slightly narrower spire angle and slightly flatter whorl outlines (S. symmetricus possibly includes S. delli vellai and S. quennelli, from the early Nukumaruan and Mangapanian, respectively). The abundant Hawke's Bay Nukumaruan species S. waikopiroensis (almost certainly the same taxon as S. uttleyi, based on the more coarsely sculptured variants in the population) has more numerous, lower, more closely spaced spiral cords than the S. symmetricus group, and is closer to the living, northern, warm-water species S. maorius (Powell, 1940) and S. mixtus Finlay, 1930, so is probably part of the variation of the "Recent" species S. pagoda (Reeve, 1849). S. waikopiroensis occurs also in the Kupe Formation, at Wanganui (Castlecliffian). In Haweran beds of Wanganui, S. vigilax is a small species with prominently single-keeled whorls (cord B predominates), apparently also related to the living, northern, warm-water S. pagoda (Reeve). Earlier species of the genus are S. huttoni (Opoitian-Nukumaruan; Pl. 361), with only two prominent cords; S. procellosus (Opoitian) with one prominent cord low on the whorls and a weaker one high on the whorls; and S. propagoda (Mangapanian) with many low primary, secondary and tertiary cords.
Distribution: Nukumaruan-Recent. Recent, New Zealand (types of T. symmetrica and Z. delli delli); Castlecliff, Wanganui, Castlecliffian (types of Z. delli murdochi, Z. delli granti, Z. shepherdi); SE Wairarapa, early Nukumaruan (type of Z. delli vellai). Abundant in siltstone beds along the Castlecliff-Kai-Iwi coast, Wanganui (Castlecliffian); Z. delli is common in large bays and off ocean beaches in a few metres of water around central New Zealand at present, and probably intergrades with S. symmetricus, the more strongly scuptured form living at Stewart Island at present.
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)