The warm temperate South-east Pacific coast hosts extensive kelp forests that provide protected habitats to benthic organisms such as sponges. To soundly understand the interactions between kelps and sponges, a prior taxonomic identification of the associated species is necessary. This study aimed to report cryptic sponges found associated with the inner walls of the holdfast of the kelp Lessonia trabeculata, opportunistically collected in the upwelling area of San Juan de Marcona (15°S, Peru). Three sponges were identified including one Calcarea, Clathrina antofagastensis, and two Demospongiae, Johannesia reticulosa and Haliclona (Halichoclona) paracas. None of them was previously known to occur associated with kelps. These findings highlight the importance of exploring these less-studied (biogenic) substrates to uncover hidden marine biodiversity and the need for observational or experimental studies addressing the interactions developed between kelps and their epiphytozoans.