Calyptospadix cerulea Clarke, 1882: colony silhouette (A), underwater image of a colony colonizing a demosponge Halichondria panicea (Pallas, 1766) (B), relaxed polyp with characteristic single distal whorl of tentacles (C), close up of branch with polyps with contracted tentacles (D), epizootic Aurelia aurita (Linnaeus, 1758) polyps (E) and Gonothyraea loveni (Allman, 1859) (F) growing on colonies of C. cerulea, nematocysts of living C. cerulea colony, white arrows – euryteles, black arrows – desmonemes (G), pseudohydrotheca covering polyp base (H).