Question:

Which of the following is not related to porifers?

Updated On: Jul 27, 2022
  • choanocytes
  • myocytes
  • cnidoblasts
  • thesocytes
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The Correct Option is C

Solution and Explanation

Cnidocytes, also known as cnidoblasts or nematocytes, are prey-capture and defensive cells unique to and present in all animals of the phylum cnidaria (corals, sea anemones. Hydra, jellyfish etc.). Cnidocytes contain a characteristic subcellular organelle named cnidocyst (also cnida or nematocyst) which contains the toxic structure fired 2nd stage larva 1 st stage larva at the target animal. The cnidocysts are composed of a hollow coiled thread-like structure attached to the bulb-shaped nematocyst capsule body. The externally-oriented side of a cnidocyte cell also has a hair-like trigger on it, called the cnidocil. When the trigger is activated the cell "fires" - the shaft of the cnidocyst penetrates the target and the hollow thread is everted into the target organism body. This discharge is one of the fastest biological processes, takes no more than a few microseconds and reaches accelerations of about 40,000g. Following penetration, the toxic content of the nematocyst is injected into the target organism. The rapid activity of the injected neurotoxins serves to immediately paralyze the mobile prey, thus allowing the sessile cnidarian to devour it.
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Notes on Classification Of Animals

Concepts Used:

Classification of Animals

Classification of Animal Kingdom:

One of the most fundamental forms of classification of animals is the presence or absence of the notochord. Hence, two major groups exist, namely: Chordates and Non-chordates

Non-chordates and the Chordates-

  • The notochord is a flexible rod made out of a material similar to cartilage. If an animal has a notochord during any stage of its life, it is classified as a chordate. Contrary to popular belief, chordates do not exclusively include vertebrates.
  • There are invertebrates that possess a notochord during some point in their lives and hence, are classified as chordates. Thus all vertebrates are chordates but not all chordates are vertebrates.

Non-chordates-

  • Non-chordates are animals without a notochord – the rod-like elastic structure that supports the body. This phylum consists of a small group of worm-like, marine species with an organ-system level of organization.
  • Members of phylum Porifera, Coelenterata, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata and Hemichordata fall under Non-chordates

Vertebrates Classification:

The subphylum Vertebrata is divided into five classes of vertebrates. These five classes of vertebrates comprise of all the species of animals and have developed vertebral column as well as an internal skeleton.

Other characteristic features of vertebrates are-

  • Presence of a true vertebral column and internal skeleton with muscle attachment points for body movement.
  • A front-side muscular heart with two, three or four chambers.
  • Kidneys for excretion and osmoregulation
  • A paired appendages which may be fins or limbs.
  • Possess notochord during the embryonic stage.
  • Vertebrates are the only chordates to possess a brain as a part of the central nervous system.

Classification of Vertebrates-

  • Pisces
  • Amphibia
  • Reptilia
  • Aves
  • Mammalia