VARIATION IN LINEAR DIMENSIONS, TEST WEIGHT AND AMBULACRAL PORES IN THE SAND DOLLAR, ECHINARACHNIUS PARMA (LAMARCK)

Abstract

1. The widespread occurrence of skeletal variation in echinoids is indicated. 2. Variation in respect to several characteristics of the test has been studied in the sand dollar Echinarachnius parma (Lamarck) as it occurs in a number of New England localities. 3. Evidence is presented that indicates a tendency for these animals to produce tests longer than wide when living in flowing water and wider than long when living on surf-swept beaches. 4. In this species, as Raup (1958) reported earlier for Dendraster on our west coast, tests tend to be heavier at comparable sizes in populations living in colder water than those of warmer localities. 5. Populations vary from one another in numbers of pore-pairs in the petaloid areas of the ambulacra of individuals at comparable sizes, but no consistent correlations with environmental factors have been detected.