structure of hydra. cross-section of hydra polyp.

hydra cnidaria hydrozoa vulgaris freshwater polyp animal hydroid morphology structure anatomy organism diagram zoology biology drawing illustration english title scheme schema vector ectoderma mesogloea endoderma hypostome tentacle mesoglea crosssection internal educational material cnidocyte cnidocil nematocyst capsule cnidoblast nematocyte cnidocyst cnida