1
Hemichordata and Invertebrate Chordates
Chapter 17 Notes
2
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
3
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
4
Hemichordata
• Reproduction:– Dioecious (Acorn worms)• Ciliated larve “tornaria”
– Asexual (Pterobranchia)• Budding
• Nervous System– Dorsal & ventral nerve tracts– No major ganglia– Unspecialized sensory structures
5
Phylum Hemichordata
• Characteristics– Marine– Soft Bodied & Worm-like– Deuterostomate – anus forms from blastopore– Body divided into 3 Regions• Proboscis• Collar• Trunk
6
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
7
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)
8
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
9
Phylum: Chordata
• Invertebrate Chordates– Do not have a bony
vertebrae– Sub Phylum:
Urochordata• Tunicates (sea squirts)
– Sub Phylum: Cephalochordata• Lancelets
10
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
11
Lancelets
• Small, tadpole-like filter feeders
• Live In shallow marine waters
• Notochord extends from head to tail
12
Invertebrates vs. Vertebrates