Astarte Essay

Shells of the bivalve genus Astarte are known for variable morphology and polymorphism within living and fossil species. Astarte borealis, the most common living species, is recognizable and common among mid-to-high latitude North Pacific, Arctic Ocean and North Atlantic, and has been previously subdivided into several subspecies and varieties based on variations in overall shell shape. A collection of 641 Recent specimens of A. borealis from Camden Bay, northern Alaska, with intact outlines was analyzed for variability of the shell shape within the population of the single species. The analysis has important implications for morphological studies of Recent and fossil bivalve mollusks. Bivariate analysis of length vs. height and morphometric

These specimens were collected from the Pliocene marine facies of the Milky River formation at Sandy Ridge section, Alaska Peninsula (Marincovich et al., 2002)(Figure 1). Thirteen specimens from this collection were used for the distance measurement analysis based on completeness with respect to the distance measurements needed. Eleven specimens were used for the outline analysis and were chosen based on degree of outline

The EFDs are used to find the principal components of the shape variation. The principal component analysis of the normalized EFDs was accomplished in the PrinComp program of the SHAPE package (Iwata & Ukai, 2002) to efficiently summarize the information contained in these coefficients for easier interpretation. The principal component analysis converts a set of observed correlated variables and by means of orthogonal transformations, produces a set of values that are linearly uncorrelated variables or principal components (Rohlf and Archie 1984). The first principal component produced has the highest possible variance with respect to the data set. Each successive principal component has the highest possible variance with respect to the preceding component. Principal components were then visualized on a