C9

• Phylum Chordata


  Consists of a majority of species that are vertebrates (with a backbone) and minority are invertebrate chordates

  
• Chordates


  • Deuterostome coelomates with bilateral symmetry
  • Possess an endoskeleton and a closed circulatory system
  • Have segmented bodies

  
• Subphyla of Phylum Chordata

  • Cephalochordata
  • Urochordata
  • Vertebrata

  
• Notochord


  A long rod of stiffened tissue (neither cartilage nor bone) that supports the body
• Dorsal, tubular nerve cord


  Lies parallel and above the notochord and gut, with the anterior end modified into a brain
• Pharynx


  A muscular tube at the entrance to the digestive tract, with gill slits that function in feeding, respiration or both
• Postanal tail


  Exists near the anus
• Subphylum Cephalochordata - Lancelets


  • Small, fishlike animals with tapered bodies
  • Lack a well-defined head, jaws, fins and heart
  • Filter feeders that lie buried in the sand
  • Have a simple brain and closed circulation, with respiration directly across the body wall
  • Feeble swimmers that follow a simple swimming mechanism similar to fishes

  
• Subphylum Urochordata - Tunicates

  • Marine organisms covered with a gelatinous tunic
  • Larval stage resembles a tadpole with a notochord, nerve cord and tail, becoming a sessile filter feeder as an adult
  • Develop a protective covering called the tunics with two openings - incurrent siphon and excurrent siphon
• Craniates


  Animals that have a brain inside a cranium, a chamber of cartilage or bone
• The most primitive craniate fossils is called Haikouella
• Jawless armored vertebrates (e.g. Pterapsis)


  • Possess paired fins and an inner ear, with small spines at the points where paired fins develop in higher fishes
  • Have a muscular pharynx to suck bottom-dwelling organisms
• Jawless Fishes (Lampreys and Hagfishes)

  • Lack jaws and paired fins, with a cylindrical eel-like body and smooth skin lacking scales
  • Supported by a well-developed notochord and cartilaginous skeleton
• Hagfishes


  • Scavengers that look like large worms, with partial craniums on the head, no eyes, and tentacles around the mouth for sensory functions
  • Burrow on the ocean floor and prey on small invertebrates, secreting a sticky and stinky mucus when in danger
  • Produce large, thick-shelled eggs
• Lampreys


  • Parasitic on other fish, attaching with an oral, suckerlike disk to suck blood and rasp away flesh
  • Most are marine species, with some nonparasitic freshwater species
• Subphylum Vertebrata (Vertebrates)


  • Possess backbones or vertebral columns
  • Evolved with a series of bony and hardened vertebrae replacing the single, continuous notochord
  • Developed jaws from structural support for gill slits
  • Evolved fins into legs, arms and wings of higher vertebrates
  • Gradually relied less on gills and more on lungs and the circulatory system
• Conodonts (Extinct)


  • Possess mineralized mouthparts with a set of barbed hooks made of mineralized dental tissues at the anterior end of their mouth
• Gnathosomes (Jawed Fishes - Extinct)

  • Jaws evolved from skeletal rods that previously supported the gill slits, with remaining gill slits as a major site for gas exchange
  • Bony elements reinforced the notochord and pairs of fins stabilized the body
• Jawed Fish (Placoderms)


  • Streamlined bodies to reduce friction in water
  • Powerful tail muscles for propulsive force and forward motion
  • Swim bladder provides adjustable buoyancy
• Jawed Fish - Chondrichthyes (Cartilaginous Fishes)


  • Skeleton of cartilage, with a streamlined body, gill slits, fins, and small placoid scales
  • Respiration solely through gills
  • Includes sharks, skates, rays and chimaeras

  
• Sharks


  • Formidable predators with powerful jaws and replaceable teeth
  • Well developed sense organs that can locate prey, including electroreceptors
• Rays


  • Flattened bodies that live on the ocean bottom, feeding on shelled invertebrates with their flattened teeth
  • Some can jolt prey with electricity or sting with a venomous tail spine
• Chimaeras


  • Feed mostly on mollusks, with a venom gland in front of the dorsal fin
  • Almost scaleless, with a bulky body and a slender tail resembling a rat
• Jawed Fish - Osteichthyes (Bony Fishes)


  • Skeleton of bones, which provide strong support and serve as a storage site for calcium
  • Respiration solely through gills
  • Divided into ray-finned, lobe-finned, and lungfishes
• Ray-finned Fishes


  • Most bony fishes, with highly maneuverable fins supported by rays that originate from the dermis and attach to the internal skeleton
• Lobe-finned Fishes


  • Bear fleshy extensions with some skeletal elements on their ventral fins, similar in structure and position to the limbs of tetrapods
• Lungfishes


  • Have gills and one or a pair of 'lungs' that are modified gut wall outpouchings, requiring them to surface and gulp air to avoid drowning
• Amphibians


  • First successful land vertebrates, with either four legs or four-legged aquatic ancestors (tetrapods)
  • Have a body plan and mode of reproduction somewhere between 'fishes' and 'reptiles'
  • Pros of shifting to land include access to more oxygen, new food sources, and sensory input
  • Cons include variable air temperatures and lack of water support
• Amphibians


  • Bony endoskeletons and usually four legs
  • Undergo metamorphosis, with some spending their entire life in water and others laying eggs in moist places or protecting embryos internally
  • Respire through gills, lungs, and skin, but still depend on moist skin for gas exchange
• Frogs and Toads (Order Anura)


  • Distinctive with their long hind limbs that make them capable of jumping
• Amphibians


  • All have bony endoskeletons and usually have four legs
  • Undergo the metamorphosis process
  • Some spend their entire life in water, others shed their eggs into water which is also home to a free-swimming larval stage
• Amphibians adapted to life on land

  Either lay eggs in moist places or in a few cases protect embryos during development inside the moist adult body
• Amphibian respiration


  • Can respire by the use of gills and lungs but they still depend on skin and pharyngeal lining for gas exchange
  • Respiratory surfaces must be kept moist for gas exchange
  • The skin dries easily in the air, so they had not escape from water dependency fully
• Amphibian skin


  Usually thin and sometimes supplied with glands that produce toxins
• Frogs and Toads


  • Distinctive with their long hind limbs making them capable of jumping into the air and barrel through water
  • Their success on land is due to their excellent prey-grasping capability of the tongue attached at the front of the mouth
• Frogs and Toads


  • Have mucous glands, poison glands and antibiotics at their skin to protect them from diverse pathogens in aquatic habitats
  • Poisonous species has bright warning coloration
• Caecilians


  • Shaped like an earthworm/eel and they have segments
  • Most are between 4-15 inches long and up to 1 inch in diameter
  • Live burrowed in the moist / swampy forest floor where they hunt for invertebrate prey like insect's larvae and termites
• Caecilians


  • Have no limbs but do have small scales embedded in the skin that helps in the burrowing acts
  • They also lost their sight but used their sense of touch and smell to find earthworms and insect
  • Some aquatic species used electric cues
• Salamanders


  • When they walk, the body bends from side to side, much like a fish moving through water, thus, they might evolve from fish
  • Adults may retain larval features such as external gills like the axolotl

  
• Amniotes


  • The first organisms that produce shelled eggs
  • The evolution of reptiles from ancestral amphibians depends on their adaptation to become completely terrestrial
  • The evolution of the amniotic egg is extremely important as it allows them to lay eggs in terrestrial habitats