Comparisons between plants and sessile modular colonial invertebrates offer interesting parallelisms between plant and animal body plans after millions of years of divergent evolution. Among these parallelisms might be the existence and distribution of intraindividual heterogeneity in organ traits, also named subindividual variability. Subindividual variability is quantitatively important and has many consequences for plant individuals, populations and communities, and for animal consumers as well. However, could a similar process of subindividual variability occur in sea pens, which have a modular architecture similar to that of plants? In the literature of marine invertebrates very little is known about the presence and magnitude of subindividual variability in modular organisms. This study provides for the first time a quantitative assessment of subindividual variability in sea pens, analysing certain biometric features of reiterated structures that presumably have some ecological function, and offers an initial comparison of quantitative levels of subindividual variation between plants and sea pens.