Phylum Chordata
• >50,000 species
• Most in Subphylum Vertebrata
• Unifying characteristics
– Postanal tail
– Pharyngeal gill slits
– Hollow dorsal nerve chord
– Notochord
Nerve Chord
Embryonic origin from
ectodermis
Phylum Chordata
Subphylum Cephalochordata (lancelets)
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~30 Species
small, fishlike
Rapid swimmer
Spend most time
burrowed in soft
sediments
Filter-feeder
4 – 8 cm long
Food in SE Asia
Resembles Nectocaris
Locomotion
• Myomeres (chevrons)
• Tail, ventral, and dorsal
fins
• Flexible notochord
• Strong swimming
actually helps them
back into sediments
Nervous System
• Rudimentary
• Small brain –
enlargement of
nerve
• Limited sensory
structures
Digestive System
Circulatory System
• Well developed (Figure 29-8)
• Dorsal and ventral aorta plus smaller
vessels
• Major branches to key systems
• No “typical” heart – ventral blood
vessel (aorta + sinus venosus) are
contractile
Subphylum Urochordata (Tunicata)
• Sea squirts and
planktonic relatives
• ~2100 species
• Most divergent
group of chordates
• Adults would not be
confused with
chordates
• Still, very diverse
group
Divergent Characteristics
• Adults lack
– Notochord
– Dorsal hollow nerve chord
– Postanal tail
• Present in brief larval stage
• Mostly sessile
• Body covered in protective
tunic (exoskeleton)
• Tunic – proteins, carbs,
cellulose
Chordata Phylogeny
• Vertebrata and Cephalochordata are
sister groups – greatest retention of
chordate features in adults
• Tunicata diverged into five major
groups and exhibit greatest diversity of
the invertebrate chordates
Chordata Phylogeny
• Chordate ancestor may have resembled
adult enteropneusts (members of P.
Hemichordata)
• Problem, there are some opposite
patterns between the two groups (also
many chordate features opposite of
what is seen in rest of invertebrates)
Opposites
• Blood flow (poster in dorsal aorta of
amphioxus)
• Food transport (dorsal in amphioxus)
• Proposed explanation – dorsoventral
axis inversion in chordates
• Evidence – larval and adult feeding in
amphioxus inverted
Cross Section – Pharyngeal Region