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Introduction To Chordates 9. Chordata: Urochordata and Cephalochordata James Hake & Eden Berdugo What is a chordate? • Vertebrates are a subphylum of the phylum Chordata (the chordates) • Chordates are bilateral • Belong to a clade of animals known as Deuterostomia James Hake & Eden Berdugo Derived Characteristics of Chordates • • Notochord – a longitudinal, flexible rod; provides flexible skeletal support Dorsal Hollow Nerve Chord – develops into central nervous system (brain/spinal cord) http://kentsimmons.uwinnipeg.ca/16cm05/16labman05/lb7pg1_files/34-02ChordateCharacters-L.gif •Pharyngeal Slits or Clefts –grooves that develop into slits that open to the outside of the body; used in gas exchange and feeding •Muscular, Post-Anal Tail –A tail extending posterior to the anus that contains skeletal elements and muscles; propelling force in aquatic species James Hake & Eden Berdugo James Hake & Eden Berdugo Tunicates (subphylum Urochordata) Sea Tulips http://en.wikipedia.org/wiki/File:Sea-tulip.jpg Bluebell Tunicates http://upload.wikimedia.org/wikipedia/commons/9/98/Blu ebell_tunicates_Nick_Hobgood.jpg Categories • Body Cavity – Coelemate – Body cavity lost in adults • Body symmetry – Bilateral • Nervous System – Simple brains with ganglion clusters • Circulatory System – Closed circulatory system in which blood is transported – Blood circulation powered by heart http://www.mun.ca/biology/scarr/142007_Urochordata.jpg James Hake & Eden Berdugo Categories [Continued] • Digestive System: – Suspension feeders; feed by filtering sea water through pharyngeal slits, where food gets caught in a mucus lining – Two openings in body cavity: in-current and excurrent siphon • Excretory System – None • Locomotion/Musculature – Sperm are mobile, but adults are immobile • Skeletal Type – None – Invertebrate http://www.mun.ca/biology/scarr/142007_Urochordata.jpg James Hake & Eden Berdugo Categories [Continued] • Sensory Structures – Light/gravity sensing cells in the larvae • Reproduction – Hermaphrodites (ie asexual reproduction) • Gas Exchange – Absorb through pharynx • Unique Features – As larvae, they move around until they find a suitable environment to become permanently fixed to. http://www.mun.ca/biology/scarr/142007_Urochordata.jpg James Hake & Eden Berdugo Urochordata Review Adult Tunicate Larvae Tunicate http://www.mun.ca/biology/scarr/142007_Urochordata.jpg James Hake & Eden Berdugo Cephalochordata (Lancelets) Branchiostoma http://www.bethel.edu/~johgre/bio114d/LowerVerts.html http://www.mun.ca/biology/scarr/142007_Urochordata.jpg James Hake & Eden Berdugo Categories • Body Cavity – Coelomate • Body Symmetry – Bilateral Symmetry • Nervous System – Dorsal, hollow nerve cord – Hox genes control development of brain – No full-fledged brain; only have swollen tip on the anterior end of the nerve cord • Circulatory System – Contains heart – Closed Blood System http://www.mun.ca/biology/scarr/Cephalochordata.html James Hake & Eden Berdugo Categories [Continued] • • • • Digestive System – Use pharyngeal slits lined with mucous to remove tiny food particles Excretory System – Composed of paired nephridia (a tubule open to the exterior; has ciliated or flagellated cells and absorptive walls) Locomotion/Musculature – Simple swimming mechanism – Coordinated contractions of muscles in chevrons (<<<) produce movement – Muscle segments called somites Skeletal Type – No solid skeleton, but has flexible notochord – Invertebrate http://www.mun.ca/biology/scarr/Cephalochordata.html James Hake & Eden Berdugo Categories [Continued] • Sensory Structures – Poorly developed • Reproduction – Separate Sexes – Males and females have multiple paired gonads – External Fertilization • Gas Exchange – Pharynx and pharyngeal slits aid gas exchange, which occurs across the external body surface • Other Unique Features – Lancelets’ bodies aren’t hard, so little fossil evidence – Adult lancelets live in the sand with their anterior ends exposed to remove tiny food particles http://www.mun.ca/biology/scarr/Cephalochordata.html James Hake & Eden Berdugo A Review of Cephalochordata (Lancelets) http://www.bethel.edu/~johgre/bio114d/LowerVerts.html James Hake & Eden Berdugo Quiz 1. A. B. C. D. Which is not a characteristic of all chordates? Notochord Radial Symmetry Nerve Cord Pharyngeal Slits 2. True or false: Urochordates are mobile throughout their entire lives. James Hake & Eden Berdugo 3. Urochordates and cephalochordates feed by: A. Chemosynthesis B. Photosynthesis C. Pharyngeal Slits and Clefts D. All of the Above 4. Regarding their notochords… A. Urochordates keep theirs for their entire lives, and Cephalochordates do not. B. Cephalochordates keep theirs for their entire lives, and Urochordates do not. C. Both Urochordates and Cephalochordates do NOT keep theirs for their entire lives. D. Both Urochordates and Cephalochordates keep theirs for their entire lives. James Hake & Eden Berdugo Answers 1. 2. 3. 4. B False C B James Hake & Eden Berdugo