Identifying planktonic foraminiferal morphospecies: which are the important images?

Abstract

Selection of imagery that promotes accurate identification of morphotaxa is viewed as a significant problem in the taxonomy of planktonic foraminifera. Currently, imagery of taxa is sparse, apparently selected by visual judgement, and presented without information about its typicality. What is required are impartially selected images which embrace population variation to serve as training sets for reliable identification of taxa. Outlined here is a simple morphometrically-based solution, applied to the shape of shells in two orientations, in which shape variation is resolved onto three principal component axes. On the premise that the best-adapted shells are the commonest, specimens within 1 standard deviation (sd) of the trivariate mean are recognized as population exemplars suitable for use as trainers. Specimens which project at [≥]2 sd onto at least one axis are mapped as boundary specimens whose identity might be questioned. This procedure is trialled on samples of Truncorotalia crassaformis. Exemplars from the Equatorial Atlantic and Caribbean compare closely; they partially overlap with those from a Holocene Southwest Pacific population provisionally interpreted as a subtaxon, Truncorotalia crassaformis hessi.