APPLICATION OF PROTOCONCH AND APICAL ONTOGENY IN SYSTEMATICS OF THE NEW ZEALAND TURRITELLID GASTROPODS

Turritellid gastropods (family Turritellidae) in New Zealand are diverse and abundant and have a long, extremely detailed, high-resolution fossil record. In addition, many extant turritellid species apparently belonging to fossil lineages inhabit the New Zealand coastal regions, a unique situation for this formerly nearly worldwide group. Despite their abundance and relatively detailed current taxonomy, the systematics of both the Recent and fossil New Zealand turritellids remains unclear and little detailed work has been carried out on them since Marwick's work through the 1970s. This situation hinders application of the group to problems of macroevolution and paleoceanographic reconstruction.

Of crucial importance to turritellid systematics are features of the protoconch and apical ontogeny (the order in which spiral ornamentation occurs). Protoconch morphology appears to vary little within genera (despite the varying morphologies known within the family), and various workers have shown that lineages can be traced based on apical ontogeny. The technique used to describe these features in the past (light microscopy), however, has been shown to be frequently inadequate for their consistent characterization.

We have obtained new data from the first known scanning electron micrographs (SEMs) of three nominal genera of fossil and Recent New Zealand turritellids. Preliminary analysis suggests: 1) that SEMs do indeed reveal features not visible in light microscopy, and 2) that protoconch form and apical ontogeny can be used to distinguish genera in these animals. These data will form part of a larger data set that will include genetic sequences of Recent species, aiming ultimately at a phylogenetic analysis using shell and molecular characters.