General Characters, Example of Urochordata

Defination 

• Urochordates are put under sub phylum of Chordata , filter feeder and marine animals commonly called as sea Squirts or tunicata.

General Characters 

• They are mostly marine, colonial or solitary but some are pelagic also.

• Body is covered by test that is made up of Tunicin similar to cellulose or polysaccharide hence called as Tunicata.

• Animals are bilateral symmetrical, Triploblastic with organ system evel of organisation.

• Notochord is present in tail region of larval but not in adult because tail is absent in adult.

• Adult are sessile but larvae are free swimming.

• Alimentary canal is complete with large pharynx and endostyle.

• Respiration takes place through gill or test but two to many gills slits are also present.

• A dorsal atrial aperture and a terminal branchial aperture is present .

• Neural gland, pyloric gland and nephrocyte are present as excretory organ.

• A ventral tubular heart is present with open blood vascular system.

• Vanadocytes are present to extract the vanadium from the sea water.

• Reproduction is mostly sexual but some reproduce by budding also.

• Development is indirect with Retrogressive metamorphosis. And fertilisation is external.

Example of Urochordates

Ascidia

• It is commonly known as sea Squirts.

• Body of Ascidia is barrel shaped and attached with the substrate with branchial siphon.

• It has two prominent siphon to take water and food though filter feeding.

• It has a tough test made up of polysaccharide called as Tunicin.

• Larval of Ascidia is called as Tadpole which has dorsal nerve cord, pharyngeal gill slit and post anal tail.

• During metamorphosis, Larva lost tail and assume sac like body.

• Ascidia has sac like body and filter feeder in nature.

• It is hermaphrodite. Male and female gonad are found on same animal.

Doliolum

• Body of Doliolum is small, barrel shaped and transparent.

• Atrial and branchial siphon are present. First is located in front of body and other is back side of body.

• There are eight circular muscle bands are present.

• They use cilia to take water for feeding the phytoplankton 

• They use circular muscle to generate rapid and jerky movement.

• They exhibit alternate of generation with sexual and asexual phase.

• Buccal siphon is present at anterior end of body with sensory receptors.

• About two third of body contains gills slits.

• Doliolum has an endostyle to secrete mucus sheath to help the filter of food , called filter feeder.

Salpa

• It is transparent , barrel shaped animal covered by gelatinous sheath.

• Salpa are filter feeder and feeds phytoplankton and small particle.

• It exhibit alternation of generation asexual phase called oozoid and sexual phase called gonozoid.

• It has 5 to 6 muscle band on dorsal side for movement.

• Larva of Salpa is tadpole larva which undergoes metamorphosis to form adult larva.