Short CommunicationCell-mediated immune response of postmetamorphic sea urchin juveniles against infectious stages of diatom Cylindrotheca closterium (Bacillariophyceae)

•Three cell-types of diatom Cylindrotheca closterium were capable of infection in sea urchin juveniles.•Red spherulocytes and amoebocytes were the main cell effectors to fence diatom infestation in two and three months old urchins.•The effectiveness of the inflammatory process in juveniles varied as a function of urchin age, cohort and individual cell pool.

In this study, successive infectious stages by diatom Cylindrotheca closterium (Bacillariophyceae) are described for the first time during the early development of sea urchin at low temperature (8 °C). Diatom cell-types enclosed or not by typical theca were capable of infection. As an immune response, red spherulocytes and amoebocytes migrated towards infested areas and restrained the infection spreading over shells in 2- and 3-month old urchins. Only amoebocyte cells appeared to be involved in the immune reaction of 1-month old specimens which turned out to be a less effective fence to stop infestation. The effectiveness of the inflammatory process caused by diatoms within sea urchin spines seemed to vary as a function of urchin age, cohort's type and individual cell pool.