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CNIDARIANS

26th September, 2023

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Context

  • Caribbean box jellyfish are barely a centimeter long and have no brain.

Details

  • Cnidaria is a phylum under the kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.
  • Cnidarians -- the animal group that includes jellyfish, sea anemones, and coral -- are brainless, instead getting by with a "dispersed" central nervous system.
  • Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey.
  • Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick.
  • Cnidarians mostly have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes.
  • Both forms have a single orifice and body cavity that are used for digestion and respiration.
  • Not all cnidarians reproduce sexually, but many species have complex life cycles of asexual polyp stages and sexual medusae stages.
  • Cnidarians are distinguished from all other animals by having cnidocytes that fire harpoon-like structures and are usually used mainly to capture prey. In some species, cnidocytes can also be used as anchors.

PRACTICE QUESTION

Q. Consider the following statements.

1.Cnidarians are brainless, instead getting by with a "dispersed" central nervous system.

2.Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey.

3.Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick.

How many of the above are incorrect?

A) Only 1

B) Only 2

C) All 3

D) None

Answer: D) None