Phylum Chordata Characteristics and Classification

Characteristics of Phylum Chordata

Classification of Chordata:

3 Groups Linking to Vertebrates and Invertebrates:

There are 3 groups of taxons that link vertebrates to invertebrates. These are

• Phylum Hemochordata – never have a notchord
• Subphylum Urochordata – have notochord, but never vertebrae
• Subphylum Cephalochordata – have notochord but never vertebrae

The subphyla Urochordata and Cephalochordata are often referred to as the invertebrate chordata.

Subphylum Urochordata:

Below are the characterists of subphylum urochordata:

• Includes the tunicates or sea quirts
• They are sessile, barrel shaped, marine animals
• Urochordata are sometimes mistaken for sponges
• Adults develop tunics (a loose gown-like garment worm in ancient Greece) that are thick coats composed principally of cellulose.
• Most species are filter feeders

Subphylum Cephalochordata:

Below are few of the characteristics of Subphylum Cephalochordata

• Includes the lancelets or Amphioxus
• These are small, translucent, fishlike animals
• They are segmented and pointed at both ends
• They are found in shallow seas where they burrow in the sand
• Like the tunicates they are filter feeders

Subphylum Vertebrata

Characteristics of Subphylum Vertebrata:

• Possess a notochord
• Notochord in vertibrates usually replaced by vertebrata in vertebrates
• Forms the chief skeletal axis of the body
• Possess Pharyngal gill slits at least some time in thier lives
• Have a Dorsal hollow nerve cord
• Have a post anal tail

Body can be divided in to three regions, these are

• Possess an endoskeleton made up of cranium (skull), vertebral column (spine), visceral arches (rib cages), limb girdles (hip and collar bone) and two pairs of jointed appendage (arms and legs).
• Endoskeleton composed of bone or cartilage
• Have a well developed, closed circulatory system with a dorsal heart
• Possess a centralized nervous system with a brain
• Have a 2 image forming eyes.
• The excretory system is compact with paired kidneys
• Sexes are distinct and separate
• The digestive system is complete, is ventral to the spine column and possesses two large digestive glands, the liver and pancreas
• Coelom is large and well developed and filled with internal organ systems.

Classification of Subphylum Vertebrata:

Class Agnatha:

• These are the jawless (no jaws) fishes.
• They have no paired appendages
• They are cold blooded and fish-like
• Living examples includes lampreys and hagfish
• Members of this class are often called the first fishes
• Fossil members of this group represented by the ostracoderms which were armor plated fishes living on the bottom, obtained food by sucking up sediments and sorting out nutrients, essentially filter feeders.

Class Chondrichthyes:

• This class includes fishes with jaws with cartilaginous skeletons. Their skeletons is made of cartilage and is not made of bone
• Possessions of jaws gives organisms a distinct advantage over those without jaws.

1- Many biologist believe the front gills arches of jaw-less fishes are homologous to the upper and lower jaws of more advanced vertebrates.

2- Evolutionists believe the front and lower gill arches were modified over time to form the jaws of more advanced vertebrates.

• Members of this class are commonly called the cartilaginous fish.
• They are cold blooded
• They usually have powerful swimming muscles
• Includes sharks, rays, dogfish.
• with the exception of the whale, sharks are the largest living vertebrates and large sharks may reach 40 to 50 feet in length.

Class Osteichthyes:

• These are fishes with jaws and skeletons made of bones
• Members of this classes are called the bony fishes.
• They are cold blooded
• Respiration is accomplished by gills covered by a bony gill flap called the operculum.
• Most have a swim bladder
• Usually has paired fins that may be of the ray-finned or lobe-finned type
• Includes bass, perch,eel, bluegill, catfish and most of the other common fish in Tennessee.

Class Amphibia:

• They usually have 4 limbs (tetrapod)
• Are cold blooded
• Amphibia means “both life” or “double life” and members of the class usually have aquatic and terrestrial stages in their life cycles
• Aquatic larval forms usually breath by gills that are lost during metamorphosis and adults breathe by lungs.
• Skin is moist and susceptible to desiccation
• Limbs usually have 5 fingers
• Includes frogs, toads and salamanders.

Class Reptilia

• Usually have 4 limbs (tetrapod)
• Are cold blooded
• Reptilia means creep or crawl
• Reptiles have dry scaly skin that is not normally susceptible to desiccation
• Reptiles breath by means of lungs
• Includes turtles, lizards, snakes, crocodiles, and alligators

Class Aves

• Usually have 4 limbs (tetrapod)
• Are warm-blooded
• This is the first time we have used the term warm-blooded what it means is to be cold blooded or warm blooded
• A Cold blooded animals is one whose body temperature varies according to the temperature of its surroundings.
• A Warm blooded animal is one of that can regulate its body temperature within narrow limits.
• Aves means a bird
• forelimbs modified into wings
• body covered with features

Class Mammalia

• Usually have 4 limbs (tetrapod)
• Are warm blooded
• Mammalia means breast
• Young are nourished after birth by secretions of the mammary glands of the mother
• Bodies normally covered by hair at some stage of their existance
• Examples include squirrel, bats, monkeys and man