hemichordata and invertebrate chordates l.
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Hemichordata and Invertebrate Chordates. Phylum Hemichordata. Characteristics of Hemichordata:-. All live marine environments. Bilaterally symmetrical. Body divided into three sections, a proboscis, a collar and a trunk. Body cavity a true coelom divided into three cavities.

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phylum hemichordata
Phylum Hemichordata

Characteristics of Hemichordata:-

All live marine environments.

Bilaterally symmetrical.

Body divided into three sections, a proboscis, a collar and a trunk.

Body cavity a true

coelom divided into

three cavities.

Complete digestive tract, feeds on fine particles in the water.

Dorsal, sometimes tubular, nerve cord.

class enteropneusta
Class Enteropneusta

Marine worms

Ciliated epidermis and glands

cover acorn worms

Burrow in sandy and muddy substrates

Common name ‘acorn worms’

maintenance functions
Maintenance Functions

Ventral Mouth

Lateral Pharyngeal slits,few to several hundred

Cilia and mucus assist acorn worms in feeding

Ciliary tracts converge near the mouth and form a mucoid string that enters the mouth

nervous system
Nervous system
  • Ectodermal in origin
  • Lies at the base of the ciliated epidermis
  • Consist of dorsal and ventral nerve tracts
  • No major ganglia
  • Sensory receptors are unspecialized
  • Simple diffusion of metabolic waste
  • Cilia associated with Pharyngeal slits circulate water into mouth and out of body
  • Gas exchange as water passes through pharyngeal slits
circulatory system
Circulatory system
  • Colorless blood moves nutrients and wastes
  • Dorsal and ventral contractile vessel
  • Blood moves anteriorly in dorsal
  • Posteriorly in ventral vessel
  • Branches from theses vessels lead to open sinuses (Partially open circulatory system)
  • Anterior flowing blood moves through glomerulus (excretory organ)
  • Waste filtered into proboscis coelom and out through pores found in wall of proboscis
reproduction and development
Reproduction and Development



External Fertilization

class pterobranchia
Class Pterobranchia

pteron- wing

branchia- gill

Deep marine water

Some live in shallow waters

maintenance functions16
Maintenance Functions

Filter feeders

Cilia on tentacles trap and transport

Food to mouth

Respiration and excretory exchange by diffusion

reproduction and development17
Reproduction and Development

Asexual budding is common and responsible for colony formation

Also some posses one or two gonads

Most species are dioecious

External fertilization

Planula-like larva (cnidarian)

Settles to a substrate, forms cocoon and metamorphoses into an adult

phylum chordata
Phylum Chordata

Characteristic of the chordates

Deuterostome embryo development Notochord, phayngeal slits or pouches, dorsal tubular nerve cord, and postanal tail

Coelomate animals

Bilateral symmetry


Two major groups: nonvertebrate chordates and vertebrates

subphylum urochordata
Subphylum Urochordata
  • Uro, tail and chorda, cord
  • Class ascidians
    • Tunicates or sea squirts
Solitaire or colonial
  • Sessile adults
  • Attach to solid substrates
  • two siphons that permit seawater to circulate through the body
  • Oral siphon also the mouth
  • Atrial siphon
body wall
Body wall
  • Tunic- gown
  • Connective tissue like covering
  • Tough secreted by the epidermis
  • Composed of proteins

Salts, cellulose

  • Stolons extensions of tunic help root
maintenance functions23
Maintenance Functions
  • Longitudinal and circular muscles below the body wall epithelium
  • Nervous system largely confined to body wall
  • Forms nerve plexus with a single ganglion between oral and atrial opening
  • Sensitive to mechanical and chemical stimuli around siphon but no complex sensory organs
reproduction and development24
Reproduction and Development
  • Tadpole larva
  • Attaches to substrate by adhesive papillae located below the mouth
  • During development internal structures rotate 1800 bending the digestive tract into a U-shape
reproduction and development25
Reproduction and Development
  • Monoecious
  • Self fertilization and cross fertilization
subphylum cephalochordata
Subphylum Cephalochordata
  • Elongated laterally flattened nearly transparent
  • Lancelets
  • Size up to 5 cm tadpole like animals
  • All four chordate characteristics persist throughout life
  • Shallow waters
  • genera Branchiostoma (Amphioxus)
reproduction and development27
Reproduction and Development
  • Dioecious
  • Gonads shed gametes into the atrium
  • Leave the body through the atriopore
  • External fertilization
  • Bilaterally symmetrical larva
  • Larva free swimming
  • Larva Settle to substrate then metamorph into adults
maintenance function
Maintenance Function
  • Filter feeders
  • Buried in sandy substrate
  • Mouth pointed upward
Cilia on lateral surfaces of gill sweep water into mouth
  • Food sorted in the cirri
  • Edible particles move along cilia to the gut
No true heart
  • Contractile waves in the walls of major vessels propel blood
  • Blood contains amoeboid cells and bathes tissues in open spaces
Excretory tubules are modified coelomic cells closely associated with blood vessels.
  • Coelom reduced- restricted to canals near the gill bars, endostyle and the gonads