General Characteristics of CNIDARIA

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Questions and Answers

What type of body symmetry do cnidarians exhibit?

  • Bilateral symmetry
  • Radial symmetry (correct)
  • Asymmetrical
  • None of the above

Which of the following statements is true regarding the nervous system of cnidarians?

  • Their nerve cells are only located in the gastrodermis.
  • They have no nervous system at all.
  • They possess a simple nervous system forming a nerve net. (correct)
  • They possess a complex brain and CNS.

What is the primary function of cnidae in cnidarians?

  • Stinging or adhesion (correct)
  • Locomotion
  • Respiration
  • Digestion

In the class Hydrozoa, how is the enteron structured?

<p>It is not divided by mesenteries. (B)</p> Signup and view all the answers

Which of the following is a characteristic of the medusa form in Scyphozoa?

<p>Medusa is usually the dominant form. (C)</p> Signup and view all the answers

What type of reproduction do most polypoid hydrozoans primarily undergo?

<p>Asexual reproduction (A)</p> Signup and view all the answers

What type of skeletal system do Hydrozoa typically possess?

<p>External and usually chitinous (D)</p> Signup and view all the answers

Which class of cnidarians includes organisms known for their colonial and polymorphic characteristics, like Obelia?

<p>Hydrozoa (C)</p> Signup and view all the answers

What distinguishes scyphomedusa from hydromedusa?

<p>Absence of velum (C)</p> Signup and view all the answers

What feature is notable about Cubozoa medusa?

<p>Square-shaped body with tentacles at the corners (C)</p> Signup and view all the answers

What type of symmetry do comb jellies exhibit?

<p>Biradial symmetry (B)</p> Signup and view all the answers

What is unique about the reproductive system of most comb jellies?

<p>They are hermaphroditic (C)</p> Signup and view all the answers

What type of cells are involved in prey capture in comb jellies?

<p>Colloblasts (A)</p> Signup and view all the answers

What is the function of siphonoglyphs in anthozoa?

<p>To move water into the gastrovascular cavity (B)</p> Signup and view all the answers

Which statement is true regarding the mesoglea in both scyphomedusa and anthozoa?

<p>It contains amoeboid mesenchyme cells (C)</p> Signup and view all the answers

What feature enhances the predatory behavior of Cubozoa medusa?

<p>Developed swimming capabilities (D)</p> Signup and view all the answers

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Study Notes

General Characteristics of CNIDARIA

  • Radially symmetrical, facilitating food capture from all directions.
  • Diploblastic structure with epidermis and gastrodermis separated by mesoglea.
  • Single gastrovascular cavity functioning as both mouth and anus.
  • Absence of a head, brain, and central nervous system; features a simple nerve net.
  • Sense organs include statocysts and ocelli.
  • Skeletal structures may be horny or calcareous, can be internal or external.
  • No specialized structures for respiration, excretion, or transport (except in some jellyfish).
  • Unique cnidae in cnidocytes, with nematocysts being the most common type.
  • Exhibits polymorphism, existing as solitary or colonial forms (polyp or medusa).
  • Four classes identified: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa.

Class HYDROZOA

  • Enteron is not partitioned by mesenteries.
  • Tentacles of polyps typically solid, and mesoglea is acellular.
  • Cnidocytes localized only in the epidermis.
  • External chitinous skeleton predominates.
  • Hydromedusa are smaller and serve as gamete producers with ectodermal gametes.
  • Notable genera include Hydra, Gonionemus, and Obelia.

Class SCYPHOZOA

  • Medusa form is dominant; differs from hydromedusa due to the absence of velum (acraspedote).
  • Tentacles are short and may be notched along the margin.
  • Mesoglea contains amoeboid mesenchyme cells.
  • Cnidocytes present in both gastrodermis and epidermis, with gastrodermal gametes.

Class CUBOZOA (Box Jelly)

  • Medusa is square-shaped with tentacles hanging from the corners.
  • Known for strong swimming abilities and being voracious fish predators.
  • Possess advanced image-forming eyes for navigation.
  • Stings from some species (e.g., Chironex) can be lethal to humans.

Class ANTHOZOA (Sea Anemones and Coral)

  • Only polyp form is predominant, exhibiting limited mobility.
  • Oral end expands into a disc with hollow tentacles encircling a slit-like mouth.
  • Gastrovascular cavity is compartmentalized by mesenteries, which contain cnidocytes and gonads.
  • Mesoglea features amoeboid mesenchyme cells, with a pharynx leading from the mouth.

Class CTENOPHORA (Comb Jelly)

  • Features biradial symmetry and is transparent, fragile, acoelomate, and luminescent.
  • Bears eight rows of comb-like cilia for movement.
  • Largest animals moving via ciliary actions, forming musculature from gelatinous mesenchyme.
  • Lacks attached sessile life stages and is typically monomorphic.
  • Primarily hermaphroditic, developing through a cydippid larval stage.
  • Possesses a complete gut; pharynx leads to branching gastrovascular canal system with small anal pores.
  • Tentacles equipped with adhesive cells called colloblasts for trapping prey, lacking stinging nematocysts.

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