Source of Dichromatism in Two Maldanid Polychætes

Abstract

THE tubiculous Maldanid polychætes are among the most abundant infaunal components of intertidal and sub-tidal bottom communities of the North American Atlantic coast. Within their respective ranges the two species Clymenella torquata Leidy and Axiothella mucosa Andrews show a striking dichromatism: populations may be either green or orange. A population inhabiting a particular microgeographic area is always consistent, although the distance over which a colour change occurs may be only a few miles. Continuous intergraduations do not occur. A third closely related species, Euclymene collaris Claparède, does not undergo the colour change; it exists only in the orange form even where it is sympatric with the green forms of the first two. Table 1 lists the colour of populations found at each of seven macrogeographical locations sampled by me.