MORPHOMETRIC ANALYSIS OF ASTARTE BOREALIS (MOLLUSCA: BIVALVIA) OF CAMDEN BAY, NORTHERN ALASKA

The genus Astarte is known for variable shell morphology and polymorphism within living and fossil species. Astarte borealis, the most common living species, has been divided into many subspecies and varieties merely based on overall shell shape. The A. borealis is easily recognizable and common among mid to high latitude North Pacific, Arctic Ocean and North Atlantic waters making clarification of species varieties a complex issue. Ascertaining the morphological variability based on shell shape within an A. borealis population may reduce the use of subjective interpolation of potential subspecies or varieties within the species. A collection of Recent A. borealis specimens from the Camden Bay, Alaska yielding 641 specimens with outline intact were used in this study to find shell shape variability. The Recent samples were compared with 11 Pliocene A. borealis and 19 Oligocene Astarte martini. Traditional bivariate analysis of height and length were executed to find precision of variability explained by these methods. Morphometric analysis of the shell outline determined variants within a population of A. borealis and in comparison to both fossil samples. The computer program SHAPE uses elliptic Fourier coefficients of the A. borealis and A. martini shell outline to evaluate and visualize shape variation among specimens. In bivariate analysis, the Recent and Pliocene A. borealis correlation coefficient were 0.7393 and 0.7336 respectively, the Oligocene A.martini was 0.8977.The principal component (PC) analysis of the coefficients showed that the majority of the variation in the Recent A. borealis was summarized by 6 components. The overall coefficient analysis showed the 1^st PC accounted for 47.5% of the variance related to the aspect ratio of the shell, ranging from 1.09:1 to 1.26:1. The 2^nd PC of umbo position relative to central line comprised 22.7% variance and the 3^rd PC, overall shell shape (subquadrate to subtrigonal) comprised 13.1% variance.