Chordata
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Chordata. Deuterstome coelomates Four features characterize: Dorsal, hollow nerve cord Develops from ectoderm > develops into CNS: brain and spinal chord Notochord Fluid-filled cells encased in stiff, fibrous tissue Pharyngeal slits/pouches Filter feeding Postanal tail

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Chordata

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Chordata

Chordata

  • Deuterstome coelomates

  • Four features characterize:

    • Dorsal, hollow nerve cord

      • Develops from ectoderm > develops into CNS: brain and spinal chord

    • Notochord

      • Fluid-filled cells encased in stiff, fibrous tissue

    • Pharyngeal slits/pouches

      • Filter feeding

    • Postanal tail

  • Urochordata and Cephalochordata are nonvertebrate subphyla


In tetrapods

In tetrapods…

Notochord develops into the nucleus pulposus in invertebral disks


Urochordata

Urochordata

  • Tunicates and salps

  • Larvae have notochord and nerve cord

    • Plainly exhibit all of the basic characteristics of chordates

  • Difficult to discern evolutionary relationship by examining an adult

  • Secretes tunic, a tough sec composed mainly of cellulose


Chordata

  • Tail and notochord are resorbed; nervous system degenerates

  • Informal name “sea squirts” b/c some species shoot a jet of water through excurrent siphon


Cephalochordata

Cephalochordata

  • Lancelets – resemble a lancet – a small, two-edged surgical knife

  • Notochord runs entire length of the dorsal nerve cord and persists throughout the animal’s life

  • Retains chordate characters as adult

  • Filter feeders

  • Closest relatives to vertebrates

  • Hox genes for swollen tip of anterior dorsal nerve cord are expressed in the same anterior-to-posterior order in lancelets and vertebrates

    • Vertebrate brain an elaboration of simple nerve cord tip?


Chordata

  • Chordates with a head = craniates

    • Brain at anterior end of dorsal nerve cord, eyes and other sensory organs, and a skull

  • Possess two clusters of Hox genes

  • Neural crest – a collection of cells that appears near the dorsal margins of the closing neural tube

    • Cells give rise to teeth, some bones and cartilage of the skull, inner layer of skin of facial region, several types of neurons


Transition to craniates

Transition to craniates

Haikouella – 530 million years old (Cambrian explosion), 3-cm-long; suspension feeder; resembled craniates in that it had a small brain, eyes, and muscular segments, tooth-like denticles. Did not have a skull.


Chordata

Haikouichthys – had a skull made of cartilage. Classified as a true craniate.


Hagfish

Hagfish


Hagfish1

Hagfish

  • Skull of cartilage but lack jaws and vertebrae

  • Use segmented muscles to exert force against notochord

  • Small brain, eyes, ears, and a nasal opening

  • Tooth-like formations of keratin in mouth

  • Secretes mucus as defense

  • Not considered fishes


Nom nom

Nom nom


Vertebrates cephalaspidomorphi

VertebratesCephalaspidomorphi

  • Gene duplication allowed development of innovations in the nervous system and skeleton

  • Vertebrae takes over mechanical role of notochord

  • Lampreys are oldest living lineage of vertebrates

  • Mostly parasitic

  • Skeleton of cartilage with no collagen

  • Pairs of cartilaginous projections partially enclose nerve chord


Conodonts cone teeth

Conodonts“cone teeth”

  • 3-10-cm-long; soft-bodied with prominent eyes controlled by numerous muscles

  • Barbed hooks made of mineralized dental tissues

    • Dental elements used to date strata

  • Other innovations such as paired fins, an inner ear with two semicircular canals, and armor made of mineralized bone

  • Extinct by end of Devonian


Chordata

  • Vertebrate skeleton evolved as a structure made of unmineralized cartilage

  • Mineralization began after lampreys diverged from other vertebrates, and mineralization began in the mouth (conodont dental elements)


Gnathostomes jaw mouth

Gnathostomes“jaw mouth”

  • Grip food, slice it up.

  • Evolved from skeletal rods that supported anterior pharyngeal slits

  • Remaining slits used for respiration (since suspension feeding was no longer necessary)

  • Additional duplication of Hox genes (four, as opposed to one cluster)

  • Lateral line system – organs sensitive to vibrations


Chordata

  • Paired fins and tail allowed more efficient swimming

  • Jaws enabled gnathostomes to grab prey or bite off chunks

  • Earliest gnathostomes (placoderms and acanthodians) are extinct


Chondrichthyes cartilage fish

Chondrichthyes“cartilage fish”

  • Sharks, rays, and relatives (ratfish)

  • Skeleton composed predominately of cartilage

    • Does not mean lineage is primitive in the evolution of vertebrates

  • 750 living species

  • Large amount of oil in liver for buoyancy, but sinks of stationary

  • Locomotion and respiration, although some have spiracles that force water across shark’s gills

  • “sleep swimming”


Sharks and rays

Sharks and Rays

  • Largest sharks and rays are suspension feeders

  • Sharks have sharp vision but cannot distinguish colors

  • Nose for olfaction, not breathing

  • Detect electric fields generated by the muscle contractions of animals

  • No eardrums; sound is transmitted by body to hearing organs of inner ear


Sharks

Sharks

  • Eggs fertilized internally

  • Oviparous and ovoviviparous – eggs that hatch outside the mother and young that are born after hatching within the uterus

  • Viviparous – develop within uterus and obtain nourishment prior to birth via mother’s blood, or by eating other eggs

  • Sibling rivalry.

  • Cloaca – opening for digestive, urinary, and reproductive tract


Osteichthyes bony fish

Osteichthyes“bony fish”

  • Includes bony fishes and tetrapods

  • Aquatic osteichthyans are informally called fishes

  • Osteichthyans have ossified (bony) endoskeleton w/ hard matrix of calcium phosphate

  • Breathe by drawing water over 4 or 5 pairs of gills located in chambers covered by protective bony flap, operculum


Chordata

  • Transfer of gas from blood to swim bladder allows control of buoyancy

  • Evidence suggests lungs came first then evolved into swim bladders…

  • Skin is covered by flattened, bony scales and mucus that reduces drag


Ray finned actinopterygii ray wing fin

Ray-FinnedActinopterygii“ray wing/fin”

  • Bass, trout, perch, tuna, herring, salmon

  • Maneuvering, defense

  • Originated in fresh water

  • Taste great.


Chordata

  • Just dance

  • Birth


Ray finned sarcopterygii

Ray-FinnedSarcopterygii

  • Evolved during Devonian

  • Rod-shaped bones surrounded by a thick layer of muscle in their pectoral and pelvic fins

  • Used fins to swim and walk underwater

  • Three lineages survive: coelacanths, lungfishes, and the lineage that gave rise to tetrapods, including humans!


Chordata

  • Lungfish


Chordata

  • The Shape of Life


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