Hemichordata and Invertebrate Chordates

Phylum Hemichordata

Bilaterally symmetrical.

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

Characteristics of Hemichordata:-

All live marine environments.

Body cavity a truecoelom divided intothree cavities.

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

Dorsal, sometimes tubular, nerve cord.

Class Enteropneusta

Burrow in sandy and muddy substrates

Ciliated epidermis and glandscover acorn worms

Marine worms

Common name ‘acorn worms’

Maintenance FunctionsVentral MouthLateral 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

Enteropneusta extends its posterior end out of the burrow during defecation.

Eww!!!

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

Respiration

• 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• 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

Dioecious!!

External Fertilization pheromones

Evolutionary ties b/w hemichordatres and echinoderms

Ciliated larvae

Class Pterobranchia

pteron- wing

branchia- gill

Deep marine water

Some live in shallow waters

Body divided into three regions

Size 0.1 - 5mm

Individuals called zooids

Most live in secreted tubes in asexually produced colonies

Maintenance Functions

Filter feeders

Cilia on tentacles trap and transportFood to mouth

Respiration and excretory exchange by diffusion

Reproduction and Development

Asexual budding is common and responsible for colony formation

Also some posses one or two gonads

Most species are dioeciousExternal fertilizationPlanula-like larva (cnidarian) Settles to a substrate, forms cocoon and

metamorphoses into an adult

Phylum Chordata

Characteristic of the chordatesDeuterostome embryo development

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

Coelomate animalsBilateral symmetryEndoskeletonTwo major groups: nonvertebrate chordates

and vertebrates

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

• Tunic- gown• Connective tissue

like covering• Tough secreted by

the epidermis• Composed of

proteinsSalts, cellulose

• Stolons extensions of tunic help root

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 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 Development

• Monoecious

• Self fertilization and cross fertilization

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 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

• 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