SEXUAL DIMORPHISM OF SHELL SHAPE AND GROWTH OF VILLOSA VILLOSA (WRIGHT) AND ELLIPTIO ICTERINA (CONRAD) (BIVALVIA: UNIONIDAE)

Shell shape and growth of two unionacean species, Villosa villosaand Elliptio icterina, are analyzed with univariate and multivariatetechniques. The relationship of shape variables to size variablesis examined. Under the lognormal assumption, parametric testsof these allometric relationships are valid. Variables describingthe ventro-posterior region of the shell are shown to be thebest of those tested for discriminating between the sexes ofboth species regardless of statistical method. Neither speciesexhibits size sexual dimorphism. Shape sexual dimorphism ofV. villosa is constant during adult growth, but the more subtledimorphism of E. icterina changes as adults continue to grow. (Received 20 January 1986;