The Evolution of the Ancillinae with Special Reference to New Zealand Tertiary and Recent Species of Amalda H. & A. Adams, 1853 (Gastropoda : Olividae : Ancillinae)

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  • MICHAUX B.
    Zoology Department, Evolutionary Genetics Laboratory, Auckland University

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Other Title
  • ニュージーランド産リュウグウボタルガイ属の現生・化石種から見た腹足類マクラガイ科リュウグウボタルガイ亜科の進化
  • ニュージーランド産リュウグウボタルガイ属の現生・化石種から見た腹足類マクラガイ科リュウグウボタルガイ亜科の進化〔英文〕
  • ニュージーランドサン リュウグウボタルガイゾク ノ ゲンセイ カセキシュ カラ

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Abstract

Amalda is numerically the most important genus in the subfamily Ancillinae, but the systematics and the taxonomy of the group is poorly understood. This contribution represents and attempt to increase understanding of the evolution of this group. The study is based on New Zealand Tertiary and Recent members of the genus and relevant literature published since Olson's (1956) original work. Based on New Zealand species, it is proposed that the subgenus Alocospira be elevated to generic rank, and that three subgenera of Amalda be recognised-Gracilispira, Baryspira, and Spinaspira. On the basis of shell characteristics it is by no means certain that Gracilispira is monophyletic. Three informal groups are recognised within the subgenus Baryspira-the extinct robusta-group for large, biconic shells with extensively developed, tongue-shaped parietal callus, the mucronata-group for species with mucronate spires, and the australis-group for species with conic spires, The relationship between these species and those from other parts of the world is discussed. The disjunct distribution of Amalda and Alocospira in northern and southern hemisphere temperate waters is noted. Three hypotheses which attempt to explain this distribution pattern are discussed. A dispersalist explanation is detailed and rejected. Two vicariant explanations are also presented. Both concluded that the disjunct distribution noted for these genera is best made intelligible by reference to the breakup of Gondwana. However, these two hypotheses differ in a number of important details. In the hypothesis proposed by Kilburn (1981b), Amalda populations were carried by dispersing Gondwanic fragments and subsequently removed from tropical Indo-Pacific regions by competition with, and predation from, other Olividae. In the hypothesis presented in this paper, deep water ancestral taxa were carried on Gondwanic fragments. These ancestral taxa are then hypothesized to have given rise independently to northern and southern populations. A phylogenetic test, based on the cladistic analysis of allozymic data, is proposed to test these hypotheses.

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