Subphylum Urochordata

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Subphylum Urochordata
(Image Source: https://scopeblog.stanford.edu/2013/08/04/image-of-the-week-botryllus-organism/)

The Urochordata also known as Tunicata is a part of Phylum Chordata.

General Characteristics of Urochordates:
  • They are marine and sedentary.
  • Their body is enclosed in a test/tunica.
  • Notochord is present in the tail region in larvae (hence urochordate) and disappears in adults.
  • Alimentary canal is complete and are ciliary feeders.
  • Respiration is through numerous gill slits (Stigmata) which opens into the ectoderm lined cavity, the atrium.
  • They show open circulation. They have special corpuscles, vanadocytes (except in Herdmania) to extract vanadium from sea water and store it in blood vessels.
  • Dorsal tubular nerve chord appears only in larval stage, which in adults is replaced by a single dorsal ganglia.
  • Sense organs are in the form of receptors.
  • Excretion is by nephrocytes, pyloric gland or neural gland.
  • Asexual reproduction is by budding.
  • Mostly hermaphrodite. Their development is indirect. Free swimming ascidian larva shows retrogressive metamorphosis.
  • They possess the ability of dedifferentiation i.e. grow smaller during starvation and develop again on normalization of conditions.
  • Examples: Ascidia, Botryllus, Salpa, Oikopleura.

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