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Some ctenophores, molluscs, and flatworms eat hydroids bearing nematocysts, then store and use these stinging structures for their own defense Widespread.

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Presentation on theme: "Some ctenophores, molluscs, and flatworms eat hydroids bearing nematocysts, then store and use these stinging structures for their own defense Widespread."— Presentation transcript:

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4 Some ctenophores, molluscs, and flatworms eat hydroids bearing nematocysts, then store and use these stinging structures for their own defense Widespread in marine habitats, and a few in freshwater Most abundant in shallow marine habitats, especially in warm temperatures and tropical regions No terrestrial species Colonial hydroids are usually found attached to mollusc shells, rocks, wharves, and other animals in shallow coastal water, some species live at great depths Floating and free-swimming medusae occur in open seas and lakes, often far from shore Animals such as the Portuguese man-of-war have floats or sails by which the wind carries them Quite efficient predators of organisms that are much swifter and more complex Sometimes live symbiotically with other animals Often as commensals on the shell or other surface of their host Certain hydroids and sea anemones commonly live on snail shells inhabited by hermit crabs, providing the crabs some protection from predators

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6 Form and Function: dimorphism and polymorphism in cnidarians

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8 Medusae

9 Life Cycles In cnidarian life cycle, polyp’s and medusae play different roles Life cycle varies among cnidarian classes, but in general, a zygote develops into a motile planula larva Planula settles on a hard surface and metamorphoses into a polyp Polyp may make other polyps asexually, but eventually it produces free- swimming medusae by asexual reproduction Polyps by budding, or other specialized methods like Strobilation Medusae reproduce sexually and are dioecious A cycle that contains both an attached polyp and a swimming medusa permits organisms to take advantage of both pelagic (open water) and benthic (bottom) environments Occurs in true jellyfishes of class scyphozoa where the medusa is large and conspicuous and the polyps are typically very small Most hydroids of class hydrozoa also feature a sessile polyp stage, often in colonies, and a pelagic medusa stage There are many variations on the typical pattern

10 Continuation of Life Cycles…. Some hydrozoans have the polyp colony as not sessile but drifts across the ocean surface The Portuguese man-of-war, Physalia, is one such drifter, using an inflated polyp as a gas-filled float Other colonies are collections of both polyps and medusae where pulsating bells propel the colony through the water Several life cycles do not include medusae Anthrozoans are presumed to have diverged from an ancestor of the other cnidarians before the medusa evolved in the latter branch Other cnidarians, including the hydrozoan Hydra, probably lost the medusa secondarily Mechanism of loss is not clear in Hydra but in other hydrozoans a pattern of loss can be inferred from a comparison of modern forms Most hydrozoans release medusae that later make gametes A few forms make medusae without releasing them from the colony Gametes then form in the gonads of the medusae retained by the polyp colony Some species have only a short cuplike form surrounding the gonads In other gonads develop right on the polyp colony with no trace of a medusa body The latter organisms likely represent an extreme form of medusa retention and reduction

11 Cnidocytes

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15 Feeding, Digestion, and Epidermis

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19 Class Cubozoa

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