Morphological variation in the Pacific sand dollar Dendraster excentricus
Correlations between latitude, habitat, and morphology in the Pacific sand dollar Dendraster excentricus were identified with principal component analysis. Twenty-two lengths were measured on the oral and aboral surfaces of 615 specimens from 31 sites. Samples were divided at latitude 34°30′N (Point Conception) and into bay and coastal habitats by relative wave exposure. Principal components (PC) were estimated from a correlation matrix of sample means of log-transformed measurements. PC1 accounted for 90% of the variance and was a measure of overall size. All 22 PC1 coefficients were positive and differed significantly from 0, according to a jackknifing test. PC1 differed significantly with latitude (ANOVA, p < 0.01) but not habitat. Southern populations tended to be smaller. PC2 accounted for 5% of the variance and described overall shape. Of the 22 variables, 13 had significant coefficients that varied in sign. PC2 varied significantly with habitat (ANOVA, p < 0.05) but not latitude. In coastal populations, the peristome and petaloids tended to be more posteriorly positioned and the food grooves were branched more peripherally. These features correspond to the greater tendency for coastal specimens to use their posterior end to suspension feed.