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Hemichordata and Invertebrate Chordates

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Presentation on theme: "Hemichordata and Invertebrate Chordates"— Presentation transcript:

1 Hemichordata and Invertebrate Chordates

2 Phylum Hemichordata All live marine environments.
Characteristics of Hemichordata:- All live marine environments. Bilaterally symmetrical. Body divided into three sections, a proboscis, a collar and a trunk.

3 Body cavity a true coelom divided into three cavities.
Complete digestive tract, feeds on fine particles in the water. Dorsal, sometimes tubular, nerve cord.

4 Class Enteropneusta Marine worms Ciliated epidermis and glands
cover acorn worms Burrow in sandy and muddy substrates Common name ‘acorn worms’

5 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

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

7 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

8 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

9 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

10 Reproduction and Development
Dioecious!! pheromones External Fertilization

11 Evolutionary ties b/w hemichordatres and echinoderms
Ciliated larvae

12 Class Pterobranchia pteron- wing branchia- gill Deep marine water
Some live in shallow waters

13 Body divided into three regions
Size mm

14 Individuals called zooids

15 Most live in secreted tubes in asexually produced colonies

16 Maintenance Functions
Filter feeders Cilia on tentacles trap and transport Food to mouth Respiration and excretory exchange by diffusion

17 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

18 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 Endoskeleton Two major groups: nonvertebrate chordates and vertebrates


20 Subphylum Urochordata
Uro, tail and chorda, cord Class ascidians Tunicates or sea squirts

21 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

22 Body wall Tunic- gown Connective tissue like covering
Tough secreted by the epidermis Composed of proteins Salts, cellulose Stolons extensions of tunic help root

23 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

24 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

25 Reproduction and Development
Monoecious Self fertilization and cross fertilization

26 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)

27 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

28 Maintenance Function Filter feeders Buried in sandy substrate
Mouth pointed upward

29 Edible particles move along cilia to the gut
Cilia on lateral surfaces of gill sweep water into mouth Food sorted in the cirri Edible particles move along cilia to the gut

30 No true heart Contractile waves in the walls of major vessels propel blood Blood contains amoeboid cells and bathes tissues in open spaces

31 Excretory tubules are modified coelomic cells closely associated with blood vessels.
Coelom reduced- restricted to canals near the gill bars, endostyle and the gonads

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