Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 21g): GS165, J39/f6470, White Rock River, South Canterbury, Altonian (GNS)
Beu & Maxwell (1990): Chapter 11; p. 201; pl. 21 g.
Synonymy: Nassa (Uzita) compta Hutton 1877b, p. 596 (not of A. Adams, 1851); Nassa socialis Hutton 1886a, p. 333 (new name for Nassa compta Hutton, 1877, preoccupied); Alectrion socialis; Hima (Mima) socialis; Nassarius (Hima) tatei socialis
Type species of Mima Marwick, 1931, now regarded as a synonym of Hima Leach, 1852 (Cernohorsky 1981a, p. 175)
Description: Small for family (height 4.5-8 mm), ovate, spire 0.55-0.6 total height. Protoconch broadly conical, of 3 whorls, last half whorl with weak spiral threads, soon followed by a few weak, almost straight axial costellae, remainder smooth. Teleoconch of 4-5 whorls, evenly convex or weakly angled at about 0.67 whorl height on spire, base of last whorl convex, neck short, thick. Axial sculpture of prominent rounded, prosocline costae, typically with much wider interspaces, reaching from suture to suture on spire, and onto base on last whorl, in many shells persisting almost to neck; 9-18 (mean 11) costae on penultimate whorl. Spiral sculpture highly variable, penultimate whorl with 3-5 low, narrow, rounded or flattened cords on sides and 1-3 weaker ones on ramp; some shells with the occasional interstitial thread. Last whorl with 7-10 additional cords on base, and 4-7 much weaker and more crowded ones on neck. Cord marking shoulder angle (where present) typically slightly nodulose where it crosses axial costae, other cords usually crossing costae unchanged or with slight thickening. Aperture ovate, columella straight with a narrow ridge at base, bounded above by a shallow groove; siphonal canal short, strongly notched. Inner lip moderately callused, with a small parietal ridge. Outer lip angled at anterior end, thickened externally by a heavy, rounded varix, and bearing 7 or 8 lirae within.
Comparison: Like the other two species of Nassarius (Hima) described from New Zealand, i.e. N. (Hima) separabilis (Otaian-Altonian, Pakaurangi Point) and N. (Hima) karoroensis (Waiauan, Greymouth), N. (Hima) socialis varies greatly in shape, spire height and teleoconch sculpture. Cernohorsky (1981a, p. 177-178) was unable to detect any consistent differences in teleoconch characters between N. socialis and N. separabilis and considered them to be conspecific. Maxwell (1988a, p. 52), however, showed that these species, and N. karoroensis, can be differentiated on the basis of protoconch characters. N. socialis has a relatively small protoconch (maximum diameter 0.85-1.10 mm (mean 0.9 mm) compared with 1.15-1.45 mm (mean 1.35 mm) for N. separabilis and 1.10-1.40 mm( mean 1.25 mm) for N. karoroensis), in which spiral sculpture appears slightly before the almost straight axial costellae. In N. separabilis axial sculpture in the form of distant, opisthocyrt costellae appears well before the spirals, and the lower suture on the last whorl or so is margined by a narrow cord, which is absent from N. socialis. Spiral sculpture is weakly developed if present at all in N. karoroensis, which has one or two straight axial costellae like those in N. socialis, and lacks a margining cord. There are also some, less reliable differences in teleoconch characters N. separabilis tends to have more evenly convex whorls than the other species, and to have more numerous, more closely spaced spiral cords with less tendency to become thickened where they cross the costae. The number of axial costae per whorl varies greatly in all three species but N. socialis tends to have considerably fewer (9-18 on penultimate whorl (mean 11)) than N. separabilis (10-26 (mean 15)) or N. karoroensis (12-23 (mean 15)).
Nassarius (Hima) has a recorded range of Otaian to Tongaporutuan in New Zealand and is recorded from a wide range of lithofacies indicating depths ranging from the inner shelf to the upper bathyal zone. The subgenus is represented in southern Australia by the extant N. (Hima) mobilis (Hedley & May, 1908) (SE Australia, dredged in 55-315 m) and N. (Hima) pauperis (Gould, 1850) (Wilson 1994, p. 79), common intertidally around Sydney, and by N. (Hima) tatei Tenison-Woods, 1879 (described from Muddy Creek, Victoria (Balcombian) but recorded widely from other Neogene localities by Cernohorsky (1981a, p. 177-178)). Cernohorsky (1981a, p. 177-178) classed N. socialis as a subspecies of N. tatei, but topotypes of the latter species have a protoconch like that of N. separabilis (i.e., with a margining cord on the last whorl). Nassariidae is a highly diverse family in the tropical Pacific, but is most unusually poorly represented in New Zealand, with only 1 other very rare Miocene species, until larger species of Nassarius (Alectrion) appeared in Pleistocene rocks and the Recent fauna of Northland (of course, possibly living in Northland all along, in an area with no fossil record).
Distribution: Otaian-Altonian; Southburn Sand, White Rock River, South Canterbury, Altonian (type) and other localities in North Otago and South Canterbury, often occurring in great numbers.
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)