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Jellyfish

Medusozoa

Jellyfish are gelatinous cnidarian invertebrates with a medusa (bell-shaped) body form. In a strict sense, it refers to the true jellyfish (class Scyphozoa) and often the box jellyfish (class Cubozoa). The term is also commonly applied to some hydrozoans with a similar medusa form, including hydromedusae and siphonophores such as the Portuguese man-of-war. Jellyfish are typically ~95% water, lack a brain/heart/blood, and have a simple nerve net that lets them sense and respond to stimuli. Their tentacles bear stinging cells (cnidocytes) containing nematocysts: tiny venomous “harpoons” used to capture prey or deter threats. Most jellyfish are marine, but a few “freshwater jellyfish” exist.

Jellyfish are gelatinous cnidarian invertebrates with a medusa (bell-shaped) body form. In a strict sense, it refers to the true jellyfish (class Scyphozoa) and often the box jellyfish (class Cubozoa). The term is also commonly applied to some hydrozoans with a similar medusa form, including hydromedusae and siphonophores such as the Portuguese man-of-war. Jellyfish are typically ~95% water, lack a brain/heart/blood, and have a simple nerve net that lets them sense and respond to stimuli. Their tentacles bear stinging cells (cnidocytes) containing nematocysts: tiny venomous “harpoons” used to capture prey or deter threats. Most jellyfish are marine, but a few “freshwater jellyfish” exist.