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Hemichordata and Invertebrate Chordates

Chapter 17 Notes

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Relationship between phyla

• Animals in phyla Hemichordata & Chordata– Have pharyngeal slits• A series of openings in the pharyngeal region between

the digestive tract and the outside of the body

– A dorsal tubular nerve cord• Associated with the development of complex systems

for sensory perception, integration, and motor response

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Phylum Hemichordata• “Hemi” = half• “Chorda” = cord• Common Members:

– Acorn Worms• Burrow• Marine

– Pterobranchs• Marine• Collar has arms with many

ciliated tentacles

• Habitat:– Live in/on marine substrates

• Food:– Sediment– Suspended Organic Matter

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Hemichordata

• Reproduction:– Dioecious (Acorn worms)• Ciliated larve “tornaria”

– Asexual (Pterobranchia)• Budding

• Nervous System– Dorsal & ventral nerve tracts– No major ganglia– Unspecialized sensory structures

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Phylum Hemichordata

• Characteristics– Marine– Soft Bodied & Worm-like– Deuterostomate – anus forms from blastopore– Body divided into 3 Regions• Proboscis• Collar• Trunk

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Hemichordata

• Characteristics– Ciliated Pharyngeal slits– Open circulatory system– Complete Digestive tract– Dorsal Nerve Cord– Epidermal Nervous

system

Pterobranchs Castings on a seashore at low tide

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Phylum Chordata• Very large group

– Vertebrates – Have a back bone• have a bony vertebrae surrounding nerve cord

– Invertebrates - Do not have a back bone• examples

• Habitats:– Marine– Freshwater– Terrestrial– Aerial

• Presence of an endostyle or thyroid gland• Complete digestive tract• Ventral, contractile blood vessel (heart)

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Phylum Chordata

• 4 Characteristics Seen in all Chordates at some point of their life:1. Notochord “back cord”

a. a dorsal rod, with a sheath of connective tissue

2. Pharyngeal Slitsa. allow water to pass from pharynx to outside/ b. filter feeding mechanism

3. Dorsal Tubular Nerve cord4. Post-anal tail

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Phylum: Chordata

• Invertebrate Chordates– Do not have a bony

vertebrae– Sub Phylum:

Urochordata• Tunicates (sea squirts)

– Sub Phylum: Cephalochordata• Lancelets

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Tunicates “sea squirts”

• Sessile• Planktonic filter feeders• Development involves a

tadpole-like larva• Nervous system: – Confined to body wall– 1 ganglion - on the wall

of the pharynx– No complex sensory

organs

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Lancelets

• Small, tadpole-like filter feeders

• Live In shallow marine waters

• Notochord extends from head to tail

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Invertebrates vs. Vertebrates