ABSTRACT: Within the brittle star genus Amphipholis, individuals are generally small, gonochoric, broadcast spawners, and species often have restricted distribution areas. In contrast, A. squamata (Ophiuroidea, Echinodermata)—a species complex found worldwide—is hermaphroditic and broods its young. We used 2 complementary methods to estimate the selfing rates of this species in the northwestern Mediterranean Sea. First, we analysed 190 specimens from Les Goudes (France) using 3 co-dominant microsatellites and deduced the selfing rates from heterozygote deficiency, developing an original method to infer confidence intervals. Not a single heterozygote was discovered, leading to estimated selfing rates of 1.0 for all species, with an inferior limit between 0.77 and 0.98. In 7 other European localities, not a single heterozygote was found. Second, we analysed 91 brooders and their 369 offspring using 7 nuclear markers. All progeny had DNA fingerprints identical to those of the parents, confirming that selfing rates are very high. Such high selfing rates, by contributing to colonization success (Baker’s rule), may solve the paradox of cosmopolitism for these ophiuroids that lack a larval phase that would, in theory, ensure dispersal.