phylum chordata n.
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Phylum Chordata. *Notochord, pharyngeal slits, dorsal tubular nerve chord, and postanal tail are all present at some point in the organism’s life span. Notochord - Rod-like, supportive structure that runs along dorsal midline

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Phylum Chordata

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phylum chordata

Phylum Chordata

*Notochord, pharyngeal slits, dorsal tubular nerve chord, and postanal tail are all present at some point in the organism’s life span.


Notochord- Rod-like, supportive structure that runs along dorsal midline

  • Pharyngeal slit- Slit in pharyngeal region that allows water to pass from pharynx (area joining nasal passage to mouth passage) to the outside of body
  • Dorsal tubular nerve cord- Hollow nerve chord that runs along the mid-dorsal area.
  • Postanal tail- Tail that extends posterior to anus.
subphylum hyperotreti
Subphylum Hyperotreti
  • Class Myxini: Hagfishes
    • “Myxa” = slime (produced from slime glands)
    • No vertebrae, retain notochord
    • Tentacles around mouth
    • Live buried in mud in cold marine waters



Class Cephalaspidomorphi: Lampreys

    • Mouth (with lips) is sucker-like with teeth and tongue structure
    • Most feed on blood of prey (with anticoagulant)
    • Adults live in ocean or Great Lakes- they migrate to freshwater streams to mate and then die


class chondrichthyes
Class Chondrichthyes
  • “Chondros”= cartilage (skeleton not true bone)
    • Internal fertilization (males- clasper organ)
    • No swim bladder
    • 5 or more gill slits with no gill cover
    • Placoid scales


Subclass Elasmobranchii: Sharks, skates, rays

    • Tough skin with placoid scales (sandpaper texture) sometimes modified into “thorns” along dorsal suface. Teeth are also modified scales!
    • Rows of replaceable teeth; sometimes adapted as a “crown” of teeth
    • jaw hyostylic (single connection) or amphistylic (two connection)
    • Heterocercal tail (different sized lobes to tail)


Skate or Ray...what’s the difference?

  • Skates (order Rajiformes)
  • stocky tail w/o stinging spine 
  • Most lay eggs in case “mermaid’s purse”(oviparous)
  • Rays (order Myliobatiformes):
  • whip-like tail, usually with “stinging” spine/barb 
  • Most give birth to live young (viviparous)
  • Some rays can give an electric shock in stead of sting
  • Some rays do NOT have a defense shock/sting
  • *Skates and rays have spiracles on the dorsal surface for taking in water to gills





Rays (Stingrays)


Manta Ray: no spine/barb

shark characteristics
Shark Characteristics
  • Countershading skin camouflage (dorsal side is darker than the ventral side).
  • Some species have an eyelid-like structure called a nictitating membrane.
  • Internal ears to hear low frequency sounds
  • Large liver for buoyancy (can be up to 90% of body cavity)
  • Ampullae of Lorenzini = the electroreceptor organs enable sharks to home in on prey, which give off weak electric fields.
  • Lateral-line system sensitive to vibrations (acting like a body-length ear).
  • Because of low pectoral fins, sharks cannot swim in reverse.
  • Sharks with more than 5 gill slits are considered to be more “ancient” species.

Subclass Holocephali: Chimaeras (ratfish)

    • no spiracles
    • No scales
    • Small mouth surrounded by large lips
    • Gills covered by operculum


class osteichthyes
Class Osteichthyes
  • Osteon = bone

Major subclasses:

  • Sarcopterygii- Muscular lobes with fins and can use lungs for gas exchange
    • Lungfish
    • Coelacanths

Actinopterygii (Ray-finned fishes) – Swim bladder

    • Chondrosteans – Sturgeons (caviar!), paddlefish
    • Neopterygii – gars and bowfin
  • Scales: Ganoid (gars) ; Cycloid (bowfin)
  • Long snout with many teeth, voracious predators on small fish.
  • Restricted to North America.
  • No marine forms

Teleostei - final bony fishes

  • comprising 24,000+ species.
  • Tails homocercal in most species.
  • Scales cycloid or ctenoid, NOT ganoid.
  • Swim bladder present in most species.


• Placoid – found in sharks, they are modified on the anterior to form

teeth, they are composed of a vascular inner core of pulp, a middle

layer of dentine and a hard enamel-like outer layer of vitrodentine

• Ganoid – found in gars, bichirs and reedfish, are rhomboid in shape

and have a bony basal layer of dentine and outer layer of ganoine,

they do not overlap

• Cycloid– found in bowfin, consist of a surface bony layer and a deeper fibrous layer composed mainly of collagen

• Ctenoid – found in most teleosts, are similar to cycloid scales but

they have they have a spiny posterior margin, both cycloid and

ctenoid scales grow with the fish so they lay down concentric growth

rings and can be used to determine age and growth rates of fish.



  • Heterocercal (A): the vertebrae extend into a larger lobe of the tail.

Epicercal: the upper lobe is larger, as in sturgeons and many sharks.

Hypocercal: the lower lobe is larger, as in flying fish.

  • Protocercal (B): the tail extends around the end of the vertebral column, as in embryonic fish and hagfish.
  • Homocercal (C): the most common type of caudal fin in bony fish. The tail is symmetrical and extends beyond the end of the vertebral column.
  • Diphycercal (D): the spinal column extends horizontally all the way to the end of the tail fin, dividing it into two equal parts. Characteristic of lungfish, several other primitive fishes, and the juvenile stage of modern bony fishes.


A. caudal fin - B. dorsal fin - C. lateral line - D. nostril - E. barbelF. operculum - G. pectoral fin - H. pelvic fin - I. vent - J. anal fin