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