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Urochordata

Urochordata. Marine animals, live in all seas from shore to depth Suspension feeders Adult sessile, solitary or colonial Only larva with notochord resembles vertebrates Figures: Class Ascidiacea (sea squirts). Adult:

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Urochordata

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  1. Urochordata

  2. Marine animals, live in all seas from shore to depth • Suspension feeders • Adult sessile, solitary or colonial • Only larva with notochord resembles vertebrates • Figures: Class Ascidiacea (sea squirts)

  3. Adult: • Thick tunic protects animal and attaches the base of the body to the substratum • Water  incurrent (branchial) siphon  stigmata of the branchial basket  atrial cavity  excurrent (atrial) siphon • Finger-like sensory tentacles surround the incurrent siphon to test the size of food particles • Endostyle (ventral groove) in branchial basket produces mucus that traps food particles. Cilia move mucus towards the gut. Undigested food passes out through the anus • Heart with two large vessels that connect to smaller vessels in pharyngeal basket. Direction of pumping alternates every few beats. From: Hickman et al. 2011

  4. Larva: • Possesses all five chordate characteristics. • An acellular tunic covers the larva, and at the anterior end of the body the epidermis forms adhesive papillae under the tunic • At the end of its planktonic existence, the larva attaches with its adhesive papillae to substratum and undergoes metamorphosis From: Hickman et al. 2011

  5. Metamorphosis: • The notochord, dorsal nerve cord and tail muscles are resorbed. All that remains of the nerve cord is a ganglion. • The pharynx enlarges and the individual starts feeding for the first time From: Hickman et al. 2011

  6. Cephalochordata (lancelets) • Small (length 3-7 cm), laterally compressed, hence name lancelet • Marine, sandy bottoms of coastal temperate or tropical waters, 29 species • Previously called Amphioxus now by priority Branchiostoma. The name “amphioxus” is still used as a common name for this group From: Hickman et al. 2011

  7. Shows the five diagnostic characteristics of chordates: dorsal notochord, hollow nerve cord above notochord, pharyngeal slits, endostyle, postanal tail. The notochord stretches from the tail up into the head, hence the name cephalochordates • Suspension feeder: Water  mouth  pharyngeal slits  atrium  atriopore • Food trapped in mucus (from endostyle) lining the pharynx  intestine. Small particles  hepatic cecum phagocytosis and intracellular digestion. Undigested food  anus. Food movement by cilia not muscles. • Segmented slanted trunk musculature • Segmental spinal nerve roots. From: Hickman et al. 2011

  8. Closed circulatory system. Flow pattern similar to fish: Ventral aorta  up through branchial arteries paired dorsal aortas unpaired dorsal aorta. No heart but bulbilli at pharyngeal arches. • No erythrocytes or hemoglobin  only distribution of nutrients. • Respiration over body surface (laterally compressed) • Sexes separate, gametes  atrium  atriopore  fertilization outside From: Kardong 2009

  9. Principles of systematics

  10. Linnean Taxonomy From: Hickman et al. 2011

  11. Cladogram of living Chordates From: Hickman et al. 2011

  12. monophyly, paraphyly, polyphyly From: Hickman et al. 2011

  13. Cladogram of living Chordates From: Hickman et al. 2011

  14. Radiata Bilateria Acoelomate Pseudocoelomate Coelomate Protostomes Deuterostomes FromKardong 1998 From: Kardong 2009

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