A systematic and paleoecological study of some mollusca from the Tainui Shellbed, Castlecliff, Wanganui

Abstract

Seventeen new species and two new subspecies of Mollusca from the Tainui Shellbed are described and figured. They are: Chlamys becki, Cyamiomactra truncata intermedia, Lasaea delicatula, Myllitella putikiensis, Mysella delli, Antisolarium egenum flemingi, Lissotesta hornibrooki, Sundaya anomala, Balcis huttoni, Axymene tainuiensis, Uttleya fusiformis, Zemitrella bucsa, Liratilia robustus, Aoteatilia fossilis, Marginella (Volvarinella) sertula, M. (V.) wanganuica, Fenestrosyrinx suteri, Neoguraleus perempta, Antigulareus striata. Figures are also given of Micrelenchus caelatus caelatus (Hutton), Glaphyrina vulpicolor progenitor Finlay, Zeadmete pliocenica Finlay. The genus Brookula is discussed and the status of the subgenus Aeguispirella is determined, the species Zemitrella inconstans (Suter) reinstated, and the subspecies "nestoris" Fleming of Liratilia conguisita (Suter) given full specific rank. Fossil representatives of six phyla (Brachiopoda, Mollusca, Echinodermata, Coelenterata, Arthropoda, Polyzoa) are preserved in the Tainui Shellbed, the main constituents of these were epifaunal suspension feeders. It is possible that the several mud dwelling species are related to the occurrence of large polyzoan reefs in the Shellbed, and evidence suggests that these reefs played a major part in silt deposition. Temperature during deposition of Tainui Shellbed was warm, and the bed was estimated to have been laid down at a maximum depth of 25 fathoms. The structure of the conformable stratigraphic sequence containing the Tainui Shellbed, together with the fauna and lithology of the other shellbeds, suggest that a rise in sea level during deposition of the sequence in the Middle Pleistocene, caused a landward migration of faunal zones.