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

New Zealand Cenozoic Mollusca

Parapholas thomsoni (Suter, 1917)


(Pl. 24a): paratype?, Squadron Bay, Waiheke Island, Auckland, Otaian (AMTM586, Auckland Museum)


(Pl. 24b): paratype?, Squadron Bay, Waiheke Island, Auckland, Otaian (AMTM586, Auckland Museum)

Beu & Maxwell (1990): Chapter 11; p. 219; pl. 24 a,b.

Synonymy: Pholadidea thomsoni Suter 1917, p. 78; Parapholas aucklandica Powell, 1938a, p. 368; Beu & Maxwell 1990, p. 219, pl. 24a, b

Classification: Pholadidae: Martesiinae

Description: Size moderate for family (length 25-33 mm), subcylindrical, complete individuals (with callum) rounded anteriorly, narrower posteriorly. Callum weakly radially sculptured; remainder of shell divided into 3 parts. Anterior slope with low, narrow radial costae, crenulated by numerous, fine growth lines. Flank smooth except for growth lines, separated from anterior slope by shallow umbonal-ventral sulcus. Posterior slope with distant commarginal ridges, separated from flank by radial row of small triangular pits. Protoplax broad. Mesoplax and metaplax confluent, double, extending from protoplax almost to posterior end, broad medially, tapering behind.

Comparison: Parapholas thomsoni is easily recognised by its relatively short form and strong inflation, its hemispherical posterior end, its shell divided into three areas by two weak radial grooves, and its large, complex, dorsal accessory plates. This is the only New Zealand record of this widespread rock-boring pholad. Pholadidea differs from Parapholas in not having the posterior slope clearly defined, in not having the metaplax (if present at all) as a separate plate, and in having a siphonoplax. The figured specimen (AMTM586) is labelled "Holotype" in A.W.B. Powell's handwriting, but differs from Powell's (1938a, pl. 38, fig. 5) figure of the holotype in subtle details, and is much smaller (length 24 mm, rather than 33 mm cited by Powell). We assume it is a paratype.

When describing Parapholas aucklandica from Waiheke Island, Powell (1938a) discounted the possibility that it could be Suter's species Pholadidea thomsoni, named from a locality less than 100 km to the southeast of Waiheke Island, on Coromandel Peninsula. However, re-collection of specimens from the type locality of P. thomsoni (by Phil Moore and Lloyd Homer, when preparing the excellent description of this locality in Homer & Moore 1992, pp. 26-28), Waitete Bay, just north of Amodeo Bay, Coromandel Peninsula, showed that the better-preserved of the borers in large oysters at Anthony Bay reveals a weak second radial umbonal-ventral groove on the posterior part of the shell, and is clearly a species of Parapholas (Beu 2006, p. 301). As these specimens show no differences from Parapholas aucklandica, it appears that these are conspecific, and the earliest name for this species is Parapholas thomsoni.

Distribution: Waitakian-Otaian, "Anthony Bay" (now Waitete Bay, just north of Amodeo Bay), west coast of Coromandel Peninsula, boring in large oysters, Flemingostrea wollastoni, in limestone at low tide (type of Pholadidea thomsoni); Otaian, Squadron Bay, Waiheke Island, Auckland (type of Parapholas aucklandica), boring into greywacke boulders.

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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