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Hemichordata and Invertebrate Chordates. Phylum Hemichordata Bilaterally symmetrical. Body divided into three sections, a proboscis, a collar and a trunk.

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Presentation on theme: "Hemichordata and Invertebrate Chordates. Phylum Hemichordata Bilaterally symmetrical. Body divided into three sections, a proboscis, a collar and a trunk."— Presentation transcript:

1 Hemichordata and Invertebrate Chordates

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

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 Burrow in sandy and muddy substrates Ciliated epidermis and glands cover acorn worms Marine worms 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 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!! External Fertilization pheromones

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

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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 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 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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