While I agree that the separation of Lyropecten nodosus into two species is questionable, studies of soft parts are not likely to clarify such a situation. Generally speaking, the internal anatomy of closely related species shows less variation than the external morphology. You might expect this to be the case, if adaptation is related to environmental pressures. The external environment of a species can change dramatically in a fairly short time (geologically speaking), but the "internal environment", so to speak, is likely to remain fairly constant. Rhinoceros in Africa and tapirs in South America are believed to have common ancestry, dating from when the two continents were physically joined. Externally, the two lines have diverged morphologically, yet the two animals still have identical intestinal protozoans. The environments of the mammals have changed over time, but the environments of the protozoans (the internal anatomy of the mammals) have not. Likewise, it is easy to tell a fox from a coyote by external morphology, but you would be hard pressed to separate the two based on internal anatomy, except perhaps for minor skeletal differences. But skeleton is analygous to shell, and is not "internal anatomy" in the same sense that organs are. So, two species of Pecten may have fairly different shell morphology, yet have essentially identical internal anatomy. Either you accept the separation into species based on shell morphology as adequate, or you reject it as inadequate, but that is probably the end of the story. Paul Monfils Rhode Island