APPLICATION OF GEOMETRIC MORPHOMETRICS TO STUDY SHAPE VARIATION IN THE UNCINI OF POLYCIRRUS (TEREBELLIDAE: POLYCIRRINAE)
Glasby, C. J.
Marine Taxonomy, National Institute for Water & Atmospheric Research, PO Box 14-901, Kilbirnie, Wellington, New Zealand
A previous phylogenetic study of the species-rich genus Polycirrus by Hutchings & Glasby (presented at the Third International Polychaete Conference, Long Beach) failed as a result of insufficient morphological characters. The present study attempts to find new characters based on the overall shape of the uncini. I use the geometric morphometric method of thin-plate spline decomposed by its partial warps (TPS) to compare the uncini of thirty-eight species of Polycirrus. The genus is tentatively viewed as monophyletic on the basis of the presence of neuropodial uncini restricted largely to the abdomen (starting from segments 7-18); the monospecific genus Biremis also fits this characterisation and is included in the analysis. A revision of all Polycirrus species currently in preparation (Hutchings & Glasby) provided the (mostly) original illustrations of uncini for the present study, and they are based largely on type specimens. Twelve landmarks, representing putatively homologous points, were identified on the outline of each uncinus and digitised. Pair-wise comparisons of digitised landmarks against a hypothetical reference (average of all taxa) using the TPSPLINE program (Rohlf) captured all possible variation in shape; shapes were aligned using Procrustes superimposition (alignment step built into TPSPLINE). Shape components showing significant differences between taxa were quantified and described; they provide additional character data with which to characterise species in this difficult genus. The possibility of using partial warp scores derived from shape differences as cladistic characters is also discussed.