Subphylum Chordata: The Vertebrates

Characteristics

• Dorsal notochord: rod of tough, flexible tissue running the length of the animals body.
• Primary support
• In most chordates, before birth/hatching, it is replaced by vertebrae
• Vertebrae together are called the vertebral column or backbone
• Dorsal tubular nerve chord: 
• Passes dorsal to the notochord/or is incased in the vertebrae
• Connected with the brain at the anterior end of the cord
• Develops into spinal chord
• Pharyngeal pouches: 
• Folds of skin that develop either into gills or various structures of the lower face, neck and upper chest

Classification

• Three subphyla:
• Cephalochordata
• Retain their notochords through their entire lives
• Ex. amphioxus (lancelet): a small eel-like creature that sticks it’s head out of the sand and feeds on filtered plankton
• Urochordata
• Have notochords at the larval stage
• Ex. sea squirts: they pump water through their bodies, they keep their pharyngeal slits through adulthood
• Vetebrata
• Most familiar (95% of all chordates)
• Develop vertebral columns before birth
• We will look at this subphylum in this chapter and the next

Subphylum Vertebrata

• Vertebrate variety:
• Includes fish, amphibians, reptiles, birds, and mammals
• They live virtually every where
• From the ocean floor to the fringes of the atmosphere
• Classification:
• Ectothermic (cold-blooded): cannot generate their own body heat
• Must maintain their body temperature from external sources
• Inactive in cold temp.
• Endothermic (warm-blooded): generate their own body heat through physiological changes
• Relatively active
• Seven classes
• Ectothermic
• Agnatha
• Chondrichthyes
• Osteichthyes
• Amphibia
• Reptilia
• Endothermic
• Aves
• Mamalia
• Support
• Supported by an internal skeleton composed of bone and cartilage
• Support, protect, and surround delicate organs
• Axial skeleton: vertebral column, skull and ribs
• Appendicular skeleton: attachment of limbs
• Pectoral and pelvic girdle
• Circulation and excretion
• Closed circulatory system
• Consists of a heart and blood vessels
• Heart can have 2,3 or 4 chambers, depending on the species.
• Ventral to the vertebral column
• Blood vessels: 
• Arteries: carry blood away from the heart to body tissues
• Capillaries: thinnest branches of the arteries. 
• Pass through the body tissues. 
• Supply them with nutrients and oxygen and remove waste.
• Veins: begin with capillaries and cary blood from tissue back to the heart
• Hemoglobin: a red oxygen-carrying pigment. 
• Blood passes through a pair of kidneys to filter out waste.
• Nutrition
• There are three different types of eating habits in subphylum vertebrate:
• Herbivorous: animals that eat plans.
• Grazing animals such as horses or cows.
• Cellulose is hard to break down so the animal uses grinding teeth
• Carnivorous: animals that feed on other animals
• Sharks, lions, and eagles
• Sharp teeth, beaks, or claws
• Omnivorous: animals that eat both plans and animals.
• Varied types of teeth
• All vertebrates have an alimentary canal that is composed of:
• Esophagus
• Stomach
• Intestines
• Some have a liver, gallbladder, and pancreas
• Reproduction
• Sexes are separate
• Males have a pair of testes and females have a pair of ovaries
• Two types of fertilization:
• External fertilization
• Internal fertilization
• There are three basic methods for development:
• Oviparous: produce offspring from an egg that hatches outside the body
• Viviparous: live offspring that have been nurtured to birth inside the uterus (or similar)
• Ovoviviparous: egg remains in the mother’s body and hatches there, then emerges.
• Behavior
• Inborn
• Behavior from birth, does not need to develop
• Reflex behavior: automatic, involuntary response to stimulus
• Blinking, sucking, recoiling from pain
• Instinct behavior: elaborate behaviors, apparently the result of a stimulus or series of stimulus
• Salmon swimming upstream to spawn, mating rituals, flight or fight
• Conditioned
• A response learned by experience
• Training a dog, elephant, or seal
• Encouraged through reward/“punishment”
• Skunk spraying a dog
• Can be learned by watching other members of the species
• Intelligent
• Ability to use tools to manipulate the environment, reason out a solution to a problem, or communicate with symbols.
• Chimpanzees use rocks to open nuts and sticks to “fish” for insects
• Apes have been taught to learn sign language
• Woodpecker finch uses a cactus spike to dig out bugs
• Nervous system
• Contains:
• Brain
• Spinal cord, 
• Cranial nerves (branch from the brain)
• Spinal nerves (branch from the spinal cord)
• Sensory organs (such as eyes, ears, and taste buds)
• Five lobes of the brain
• Olfactory lobes: receive impulses from the smell receptors
• Cerebrum: controls voluntary muscle activity
• Optic lobes: receive impulses from the eyes
• Cerebellum: coordinates muscle activity and some involuntary activities
• Medulla oblongata: transports impulses to and from the spinal cord, includes some reflexes.