CH_24_STUDENT_OUTLINE_Spring_2011

CH_24_STUDENT_OUTLINE_Spring_2011 - Chapter 24: Animal...

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Unformatted text preview: Chapter 24: Animal Diversity II, Vertebrates Chordate evolutionary tree Vertebrates Craniates Tetrapods Urochordata (tunicates) Cephalochordata (lancelets) Chondrichthyes (sharks, rays) Myxini (hagfishes) Actinistia (coelacanths) Actinopterygii (ray-finned fish) Petromyzontiformes (lampreys) Dipnoi (lungfishes) Amphibia (frogs, salamanders) Reptilia (turtles, snakes crocodiles, birds) Mammalia (mammals) Dorsal nerve cord, notochord, pharyngeal gill slits, post-anal tail Vertebral column Jaws Lungs Skull Lobed fins Limbs Amniotic egg Hair, milk Fig. 24-1 Key Features of Chordates All chordates possess four features at some stage of their lives 1. Notochord (stiff flexible rod extending the length of the body) 2.Dorsal, hollow nerve chord (expands anteriorly to form brain) 3. Pharyngeal gill slits (may form respiritory organs or may appear as grooves) 4. Post-anal tail (extends past the anus) Chordates are a group of animals that includes the vertebrates , together with several closely related invertebrates . They are united by having, at some time in their life cycle, a notochord , a hollow dorsal nerve cord , pharyngeal slits , an endostyle , and a post-anal tail . The chordates consist of three subphyla: t unicates , lancelets , and v ertebrata . Tunicates larvae have a notochord and a nerve cord but these are lost in adulthood. Lancelets have a notochord and a nerve cord but NO brain or spet sense organs, and a very simple circulatory system . Vertebrata are the only sub-phylum whose members have skulls . In all vertebrata except for Hagfish , the dorsal hollow nerve cord has been surrounded with cartilaginous or bony vertebrae and the notochord generally reduced; hence hagfish are not regarded as vertebrates. (Vertebrata are c hordates with backbones or spinal columns . The grouping sometimes includes the hagfish , which have no vertebrae, but are genetically quite closely related to lampreys ) Are Humans Chordates? Only one chordate characteristic, the nerve chord, is present in adult humans; however, human embryos exhibit all four Tail will disappear completely Notochord is replaced by the backbone Gill slits (grooves) contribute to the formation of the lower jaw As an example, observe a 5-week-old human embryo picture eye heart liver tail limb bud (future leg) limb bud (future arm) gill slit Invertebrate Chordates Lack a backbone Include the lancelets and the tunicates Lancelets are fishlike filter-feeders Adults and larvae exhibit all key chordate features Tunicates (sea squirts) live in a marine environment Larvae are motile and exhibit all key chordate features Adults are sessile filter-feeders that have lost their tail and notochord (a) Lancelet nerve cord notochord gut muscle segments tail anus gill slits mouth Fig. 24-3a Invertebrate Chordates (Lancelets) Fig. 24-3b (b) Tunicate gill slits excurrent siphon (water exits) gonad gut...
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This note was uploaded on 01/16/2012 for the course BIO 1001 taught by Professor Hrinchevich during the Fall '09 term at LSU.

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CH_24_STUDENT_OUTLINE_Spring_2011 - Chapter 24: Animal...

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