The major skeletal components of six species of stalked crinoids were analyzed for Mg-calcite to compare their levels and evaluate possible correlations between Mg-calcite levels and depth and latitude of collection. An additional four species of unstalked crinoids were also examined. Mg-calcite levels in the major skeletal elements of both stalked and unstalked crinoids were three- to four-times above the accepted criterion for ‘high magnesium’ (i.e., > 4 mol% Mg-calcite) marine invertebrates. Intraspecific Mg-calcite levels of stalked crinoid body components (calyx, stalk, pinnules, arms, cirri) were similar to one another. Unstalked crinoids also had similar intraspecific levels of Mg-calcite in their body components (calyx, pinnules, arms, cirri), but significantly lower levels of Mg-calcite than did stalked crinoids. Average levels of Mg-calcite in the combined skeletal components of stalked crinoids declined with increasing depth. This difference is important as stalked crinoids generally occur at deeper depths where the polymorphs of calcium carbonate are already largely undersaturated making it more difficult to compensate for skeletal dissolution.