Empirical evaluation of the relative significance of genotypic versus environmental control over the formation of skeletal hard part morphology in marine invertebrates strengthens our interpretations of microevolutionary processes and patterns from the fossil record. Replicate clones from three genotypes of the bryozoan Electra pilosa (L.) were grown in environmentally controlled laboratory conditions. Replicate colonies for each genotype were grown in otherwise identical environmental conditions, but were fed different concentrations of the cryptophyte Rhodomonas sp. (100 cells per ml, 1,000 c/ml, 10,000 c/ml and 100,000 c/ml). Morphometric data were collected for five zooecial characters (opesial width and length, zooecial width, length and area). Data were investigated with cluster analysis, principal component analysis and analyzed with nested, Two-way ANOVA. Previous studies have reported significant food concentration effects on colony growth rates, but little effect on individual zooecial morphology. Results from this study demonstrate highly significant food concentration effects on colony growth rates. In addition, genotype and food concentration effects and their interaction are observed to be significant (p < 0.005) for all but a single case for the five zooecial characteristics. Thus, under controlled laboratory conditions, minor, but significant effects due to food concentrations can be detected in the hard part skeletal morphology of Electra pilosa.