Phylum : Hemichordata

These animals have a rudimentary structure in the collar region called stomochord, which is a structure similar to the notochord and hence the name hemichordates.

Habitat: All members of this phylum are marine.

Examples:

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Balanoglossus Saccoglossus Rhabdopleura.

Body plan: They have organ-system level of organisation.

Symmetry: They are bilaterally symmetrical.

Germ layer: They are triploblastic and coelomate animals.

Body characteristics:

  • Hemichordates have a worm-like body.
  • The body is cylindrical and is divided into an anterior proboscis, a collar and a long trunk.
  • There is a stomochord (or buccal diverticulum) in the collar region.
  • They have pharyngeal gills similar to chordates.
  • Both dorsal and ventral nerve cords are present in the body.

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Physiology:

  • Circulatory system is of open type.
  • Respiration takes place through gills.
  • Excretory organ is the proboscis gland.

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Reproduction: Sexes are separate (dioecious). Fertilisation is external.

Embryo Development: Development is indirect involving tornaria larva.

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