<p>Calcareous sponges are predominantly sciophilous and are typically found in cryptic habitats or attached to other marine organisms. While they have previously been reported as epizoic on demosponges (order Demospongiae), cases of calcareous sponges occurring as epibionts on other Calcarea representatives are exceedingly rare. This study documents the occurrence of calcareous sponge juveniles—known as olynthi (plural for olynthus)—attached to adult specimens of Calcarea. The possibility of budding was ruled out, as the juveniles were not connected to adult tissue, but instead adhered to the mineral skeletal elements (spicules) and likely belonged to different species. Two features distinguish this case from previous reports: (1) the specific regions of the adult sponge’s body to which the olynthi were attached, and (2) the unusually high number of olynthi associated with a single adult. Possible explanations for this phenomenon are discussed, as well as its potential ecological implications for both the epizoic juveniles and their host species.</p>