Sub-Phylum : Hemichordata

Classification of Animal Chordates of Class 11

  • Body is soft and unsegmented divided into proboscis, collar and trunk.
  • Bilaterally symmetrical, triploblastic, eucoelomate.
  • Digestive tract complete, respiration occurs through gills.
  • Blood colourless without corpuscles.
  • Sexes separate, development direct or indirect, larva tornaria.
  • Restriction of ‘notochord’ to the anterior part of the body draws the name Hemichordata.
  • Stomochord is an outgrowth from the anterior part of gut of Balanoglossus which was earlier considered as half notochord.
  • Resemble the chordates in having all the three primary chordate structures, namely, gill-slits, notochord and dorsal hollow nerve cord.
  • Differ from the chordates in: Lacking cephalization, metamerism, paired appendages, tail, exoskeleton, cloaca, living endoskeleton, haemoglobin and RBC.
  • Containing dorsal heart
  • Having open neurocoel
  • Bearing numerous gonads
  • Gill slits are dorsal in position instead of lateral as in chordates
  • Resemble the echinoderms in nervous system, coelom and larval form. They also have common habits, ecological niche and possess remarkable power of regeneration.
  • Important from evolutionary point of view as they link the chordates with non-chordates. E.g. Balanoglossus (tongue worm).

Sub-Phylum : Hemichordata

Fig. Balanoglossus : External features in dorsal view

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