About Jellyfish

Jellyfish are best known for their bell-shaped form and ability to deliver a painful sting. These aquatic invertebrates range from shallow coastal habitats to deep ocean waters. Jellyfish live attached to the sea floor in their initial polyp stage, but propel themselves through the water column in their medusa stage. Jellyfish range in size, from tiny creatures that are only a few inches long, to giant animals which are in excess of 3 feet across. The sting of these marine creatures can be harmful to people and requires immediate attention.

  1. Body Form and Diet

    • The many species of jellyfish are all radially symmetrical and look the same, regardless of which side you view them from. These fascinating invertebrate creatures are completely circular in body design and do not possess angles of any nature. Jellyfish are carnivores and feed on zooplankton and other microscopic organisms. This interesting marine animal paralyzes prey organisms which come into contact with nematocysts on its tentacles. Prey items are then maneuvered by the jellyfish to its mouth. Certain species of jellyfish glow at night or in deep water.

    Reproduction

    • Jellyfish undergo a complicated life cycle. The jellyfish egg develops into a tiny free-swimming larva which is termed a planula. Jellyfish planulae settle to the sea bottom after a period of hours to days and transform into tiny polyps which bear tentacles. These polyps reproduce by forming cysts, by budding or through transverse segmentation. The segmented pieces subsequently develop into medusae, which break away to become jellyfish.

    Nematocysts and Complex Vision

    • Nematocysts are secreted by the cell's cnidoblast and are effectively the most complicated secretory product known. Nematocysts discharge by everting a tubule which is far longer than the capsule that contained it. This tubule contains a toxin which stuns prey items prior to the jellyfish feeding on them. Although not typically considered to be highly developed creatures, box jellyfish possess a complex visual system. These jellyfish have 24 eyes and keep four of these permanently focused on the surface of the ocean, where they search for copepods on which to feed.

    Adaptations

    • Jellyfish are adapting to the rise in ocean temperature and drop in pH caused by increased carbon dioxide concentrations in the atmosphere. Although living coral and plankton are negatively affected, jellyfish are prospering and expanding their natural range, partly due to the reduction in numbers of the creatures which fed on them, such as sea turtles and sun fish.