Fish

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Biological diversity - fish

  • phylum Chordata - Chordates 1st appear - fossil record, cambrian explosion (500 mya)
  • Pikaia - similar appearance - modern lancelets
  • 4 defining anatomical features - chordates (synapomorphies)
  • notochord - stiffened, flexible rod cartilage. internal support+movement
  • vertebrates - modified - development intravertebral discs
  • dorsal hollow nerve cord - nerve cord expands - brain, anterior - cephalisation. begins - infolding - dorsally located ectoderm (hollow)
  • Pharyngeal slits - perforate pharynx. feeding+respiration. aquatic chordates - gills. terrestrial chordates - jaw, neck, head
  • postanal tail - muscular tail extends beyond ****. may be lost - development
  • phylum Chordata - 3 subphyla. 2 invertebrate subphyla - cephalochordata (lancelets)+ Tunicata (seasquirts+salps). 1 vertebrate subphyla - vertebrata
  • subphylum cephalo chordata - Amphioxus/"lancelets"
  • resemble fish - no developed brain+few sensory organs
  • live buried - sand
  • filter feed: "cirri" - current through pharyngeal slits
  • closed circulatory system, simple nervous system, segmented trunk musculature+respond - light
  • subphylum Tunicata - 4 classes, 3000 species = Ascidiacae (sea squirts), Sorberacea (sea tulips), Thaliacea (salps)+Appendicularia (larvaceans)
  • subphylum Tunicata - sister group - vertebrates
  • Chordate features - larvae = muscular postanal tail, notochord, dorsal nerve chord, pharyngeal "basket" slits
  • larvae = motile - settle - substrates+undergo tissue reorganisation - adult form 
  • subphylum Tunicata - share feature - vertebrates = neutral crest cells
  • cells near dorsal margins - neutral tube - folding 
  • migrate, give rise - pigment cells - epidermis (UV protection)
  • craniates - variety - jaw structures
  • subphylum Vertebrata: class Myxini
  • Hagfish - 30 species 
  • rudimentary cartilaginous skull, no vertebrae, no jaws
  • raspinf keratinous structures - use feed - carrion+injured fish
  • produce slime = antipredator strategy. cloggs gills - predators 
  • all species = marine 
  • subphylum Vertebrata: class Petromyzontida
  • Lampreys - 40 species
  • more developed skull, cartilaginous arches extend around notochord, no true vertebrae+no jaws
  • rasping keratinous teeth feed - live fish
  • migrate between freshwater+marine (anadromous)
  • subphylum vertebrata: Agnathans
  • 2 interpretations - taxonomic relationships - agnathans (jawless) - gnathostomes (jaws)
  • A = vertebrae hypothesis - lampreys = more morphological features - common - gnathostomes vertebrates 
  • B = cyclostome hypothesis - feeding apparatus suggets lampreys+hagfish more related. B supported - molecular analysis
  • subphylum Vertebrate: the Gnathostomes
  • earliest fossil vertebrates = all jawless
  • Ostracoderms - defensive bony plates - skin+cartilaginous vertebrae
  • late Devonian (450 mya) = first jawed vertebrates (Placodermi+Acanthodii)
  • jaws evolved - cartilaginous gill arches
  • subphylum Vertebrata: class Placodermi
  • 1st jawed fish - giant, armoured predators
  • Dunkleosteus…

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