chapter 34 phylum hemichordata- acorn worms

Chapter 34 Phylum Hemichordata- Acorn Worms

• Have three body regions: proboscis, collar, and trunk

• Have both a ventral and dorsal nerve cord anterior portion of dorsal is hollow

• Have pharyngeal gill slits

• Have ciliated larvae identical to echinoderms

• Have a hydrostatic skeleton

• Filter-feeders using their pharyngeal slits

Hemichordata

Chapter 34 Vertebrate Evolution and Diversity

Characteristics of Chordata

1. Notochord

2. Dorsal hollow nerve cord

3. Pharyngeal Slits

4. Muscular Postanal Tail

Notochord: This is a longitudinal, flexible rod of cartilage that is located between the gut and the dorsal nerve cord. The notochord can last into adulthood, but in most cases it is replaced by the vertebral column. The spongy material in between the vertebral bones is all that is left of the notochord.

Notochord

Dorsal, Hollow Nerve Cord: This is a tube that is formed from a plate of ectoderm that is rolled up into a tube. It is located dorsal to the notochord, it lies above the gut and beneath a single, hollow nerve cord. Due to its hollow structure the dorsal nerve cord is considered very unique. It will develop into the chordate's central nervous system.

Pharyngeal Gill Slits: These structures are openings of the upper digestive tube. During the embryonic stage these slits connect the outside to the pharynx. Early chordates used them to filter feeding. Over time the slits became modified to function in gas exchange.

Anus Tail

Muscular Post anal Tail: Most chordates have a tail extending beyond the anus. In many aquatic species the tail is equipped with skeletal and muscular tissue for movement.

Subphylum Urochordata

Subphylum Urochordata-sea squirtstunicates; cellulose in outer covering

Subphylum Urochordata

Subphylum Subphylum CephalochordataCephalochordata lanceletslancelets

Subphylum Cephalochordata lancelets

• Most like early chordates (but chordates did not descend from them)

• Marine filter feeders

• Feeble swimmers

• Muscles segments develop from blocks of mesoderm called somites that are arranged around each side of the notochord.

Subphylum Cephalochordata lancelets

Subphylum Subphylum Cephalochordata Cephalochordata lanceletslancelets

Fossils of early Fossils of early vertebratesvertebrates

Subphylum Vertebrata

• Notochord develops into a cartilaginous or boney vertebral column that surrounds and protects the spinal cord

• Have a cranium or skull that surrounds and protects the brain

• Have a advanced closed circulatory system

• Cephalization increases dramatically

Embryonic formation of the neural crest

Class Myxini-Jawless fish-Hagfish-All marine No limbs or appendages; Cartilaginous skeleton; no vertebrae

Class Myxini-Jawless fish-Hagfish

Class Myxini-Jawless fish-

Hagfish

Class Cephalaspidomorphi-lamprey-Jawless fish; Cartilaginous skeleton; No limbs or appendages; notochord has dorsal extensions that partially enclose the nerve cord “vertebrae”

Class Cephalaspidomorphi-lamprey

Class Cephalaspidomorphi-

lamprey

Class Cephalaspidomorphi-lamprey

Evolution of the Vertebrate Jaw

Ostracoderms- armored but no jaws; some were active and had paired fins

Ostracoderms

Placoderms-first jaws

• Skeletal rods called gill arches of the most anterior pharyngeal gill slits became the jaw

Placoderms

Placoderms

Chondricthyes sharks and rays• Completely cartilaginous skeleton;• Strong powerful swimmers• Must swim constantly to produce water flow over gills

due to no operculum • Lateral line system that

detects sound waves• Oviparous• Ovoviviparous• Viviparous• Cloaca

Chondricthyes sharks and rays

Osteichthyes-bony fish• Operculum-bony covering over gill arches pulls

water into mouth and over the gills

• Swim bladder- gives buoyancy regulates level in water; evolved from crude lungs

• Bony fish evolved in freshwater first and developed crude lungs to supplement gills for gas exchange; then when they returned to salt water, the opening to the lungs closed and they evolved into swim bladders

• Two chambered heart

Ray-finned fishes

Lobed-finned fishes

Lobed-finned or lobed finnedfishes; Coelacanths

Lobed-finned fishes

Osteichthyes-bony fish

Amphibians

• Three chambered heart-

• External fertilization

• Embryo and larvae forms must have water

• Epidermis is permeable to water

• No claws on toes

Amphibians

Amphibians-salamander

Amphibians-tree frog

Young tadpole

Tadpole to frog

Amniote egg

Reptiles

• Amniote egg-

• Scales composed of keratin-also protein in hair and feathers

• Three chambered with partial septum in ventricle

• Internal fertilization-

• Modern reptiles are ectotherms but many dinosaurs were endotherms

Reptiles

Care of eggs and young

Reptiles

ReptilesReptiles

Reptiles

Aves-birds

• Evolved from dinosaurs (reptiles)

• Modifications for flight-

• Internal fertilization with amniote egg

• Four-chambered heart

• Elastic air sacs connected to lungs for increased respiration and dissipation of heat

Archaeopteryx

Flightless dinosaur with protofeathers

Caudipteryx flightless but with true feathers

Aves-Birds

Mammalian Characteristics

• Hair- composed of keratin

• Endothermic

• Mammary glands

• Four-chambered heart

• Diaphragm

• Internal fertilization

• Differentiated teeth

Monotremes

Monotremes-echidnas

MonotremesMonotremes-echidnas

Monotremes-echidnas

Marsupials

Prosimians-lemurs

HominoidHominid

Primates

New world monkeys Old world monkeys prehensile tail lack prehensile tail nostrils open to the sides nostrils open downward all arboreal some ground dwelling

Apes-Hominoids Not hominidsGibbon Orangutan

Gorilla

Chimpanzee

Apes-Bonobo

Hominids-bipedal-upright stance

Lucy-Australopithecus

afarensis early hominid

Turkana boy1.7 million years old

between homo habilis and homo

erectus

chapter 34 phylum hemichordata- acorn worms

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