GNS Science

Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)

New Zealand Cenozoic Mollusca

Amalda (Spinaspira) stortha (Olson, 1956)


(Pl. 25k): holotype of A. stortha, GS2937, D45/f8479, Long Beach Shellbed, Clifden, Altonian (TM5754, GNS)

Beu & Maxwell (1990): Chapter 11; p. 232; pl. 25 k.

Synonymy: Baryspira (Spinaspira) stortha Olson 1956, p. 18; B. (Spinaspira) stortha var. irrisa Olson 1956, p. 18

Type species of Spinaspira Olson, 1956

Classification: Olividae: Ancillinae

Description: Size moderate for genus (height 30-40 mm), elongate-ovate; spire conical, 0.15-0.3 total height, covered with callus; apex small and pointed, probably indicating a conical protoconch. Last whorl with prominent, rounded, projecting, rim-like keel on periphery, sides flat or weakly convex between shoulder and edge of fasciole, contracted thence to broad anterior end. No sculpture other than growth lines. Aperture capacious, but posterior end constricted, a shallow, curved channel (posterior siphonal groove) extending up spire callus. Anterior notch deep; fasciole bounded by a rounded ridge (poorly developed in some shells), covered by smooth callus that spreads up to edge of moderately wide depressed band. Columella short, almost straight, with 6 or 7 very weak plaits separated by narrow grooves, ascending within aperture. Basal groove of variable development, bordered by a sharp ridge running from base of columellar pillar to base of parietal callus, bounded in turn by a broad sulcus running obliquely across columellar pillar. Parietal callus very prominent, thick and smooth except for obscure rugosities near posterior siphonal groove, spreading laterally as a tongue-shaped pad for up to 180°, and spreading posteriorly up to level of apex in some shells, hut in most specimens not obscuring apex. Spire callus spreading well down last whorl. Outer lip moderately prosocline, almost straight, complete examples with small denticle at end of depressed band.

Comparison: The "variety" irrisa was synonymised with Amalda stortha by Beu (1970a); the holotype differs from typical specimens only in being higher-spired. Amalda cingulata (also described from Long Beach Shellbed) was referred to Spinaspira by Olson (1956, p. 18-19); it differs from A. stortha in having a higher spire, a thinner parietal callus, and a distinctly convex last whorl, and in lacking a rim-like shoulder keel on the last whorl. A. spinigera (Otaian-Altonian, Pakaurangi Point) is much smaller than either of the Clifden species (height c. 22 mm) and has a rounded shoulder. A. pakaurangiensis (Otaian or Altonian, Pakaurangi Point, also Coral Point, Kaipara Harbour) is similar to A. stortha in most respects, but has a much wider depressed band and a much stronger fasciolar ridge. A. cincta (Otaian or Altonian, Pakaurangi Point) has a broad depressed band like that of A. pakaurangiensis but differs from it and other species of the subgenus in having a much thinner parietal callus (indistinguishable from the spire callus posteriorly), and a strongly convex last whorl; its relationships are uncertain and it is only doubtfully referred to Spinaspira.

Olson (1956, p. 17) proposed Spinaspira (as a subgenus of Baryspira) for species with a heavy, laterally spreading, tongue-like parietal callus similar to that in species of the Amalda robusta group (Pl. 22h) but having a spine-like apex. The apical whorls are normally obscured by callus, but partly abraded individuals show that the protoconch is probably conical, suggesting that the larvae had planktotrophic dispersal capabilities. Other New Zealand Amalda species, by contrast, seem to have a paucispiral protoconch and hence, limited powers of dispersal. The stratigraphical and geographical distribution of Amalda (Spinaspira) in New Zealand indicate that it was a warm-water group that arrived here during the Early Miocene. Very similar olivids are recorded from the Miocene of Europe (e.g,. the specimen from the Helvetian of Bossé, France illustrated by Cossmann (1899, pl. 3, fig. 4) under the name Baryspira glandiformis (Lamarck)). Powell (1967c, p. 198) described a Recent species, A. (Spinaspira) raoulensis, from the Kermadec Islands but this is not consubgeneric with the New Zealand species; it appears to belong in Amalda (Amalda).

Distribution: Altonian-Waiauan; Long Beach Shellbed, Clifden, Altonian (type locality of both B. stortha and B. stortha var. irrisa); Calamity Point Sandstone, Slip Point Siltstone and Lill Sand, Clifden; Burnt Hill, North Canterbury; Gisborne district. Common at Clifden localities.

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
ISBN 978-0-478-19705-1
ISSN 1177-2441
(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)


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