Quantifying Complex Shapes: Elliptical Fourier Analysis of Octocoral Sclerites

摘要

Species descriptions of most alcyonacean oc-tocorals rely heavily on the morphology of sclerites, thecalcium carbonate spicules embedded in the soft tissue.Sclerites provide taxonomic characters for species delinea-tion but require qualitative descriptions, which introduceambiguities in recognizing morphological features. Ellipti-cal Fourier analysis of the outline of sclerites was used toquantify the morphology of eight species of gorgoniid oc-tocoral in the genus Pseudopterogorgia. Sclerites from oneto seven colonies of each species were compared. Scaphoidsand spindles were examined separately; rods and octoradi-ates were excluded from the analyses because of theirmorphologic similarity across all species. Discriminantanalysis of elliptical Fourier descriptors (EFDs) was used todetermine whether the elliptical Fourier analysis could beused to identify the specimens. Sclerites were highly vari-able even within a single colony. Correct species assign-ments of individual sclerites were greater than 50% for bothscaphoids and spindles. Species assignments based on av-erages of the EFDs for each colony approached 90%. El-liptical Fourier analysis quantifies morphological differ-ences between species and measures colony variance insclerite size and shape among colonies and species. Phylo-genetic analysis based on EFDs did not capture monophy-letic groups. The quantification of complex shapes such assclerites provides an important tool in alpha taxonomy butmay be less useful in phylogenetic analyses.