Phylum Chordata
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all chordates at some time during their
development have:
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1)
2)
3)
4)
5)
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
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single, hollow nerve chord
pharyngeal gill slits
notochord
post-anal tail
endostyle or thyroid gland
divided into 3 groups (subphyla): Urochordata,
Cephalochordata, and Vertebrata
Figure 15_02
Subphylum Urochordata – tunicates (aka
sea squirts); Class Ascidiacea

are actually invertebrates, but their larvae (tadpole
larvae) have the chordate characteristics
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adult form resemble sponges attaching to surfaces
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filter feeders; have an incurrent and excurrent siphon
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covered by leathery tissue called a tunic
Figure 7.48b
Purple sea squirt
Black tower sea squirt
Robust sea squirt
Yellow sea squirt
Carpet sea squirt
Subphylum Urochordata – Class
Thaliacea (salps)
typically planktonic, colonial forms
 transparent and either spindle or
cylindrical forming long chain-like
colonies
 may be bioluminescent
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Subphylum Cephalochordata - lancelets

another invertebrate chordate; has an elongated
body with a defined head and tail
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Retains all chordate characteristics throughout life
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buries in sand and filter feeds using gill slits
Figure 7.49
The Earliest Vertebrates
- ostracoderms are the earliest known vertebrate
fossils; date back about 500 million years
- were jawless, had armor of bone in dermis, lacked
paired fins
Early Jawed Vertebrates
- jaws were thought to have been derived from
modified cartilagenous gill supports
Early Jawed Vertebrates
- jaws and paired fins (for better swimming) characteristic of
these “new” groups
- placoderms first appear about 430 mya; extinct by 400 mya
- acanthodians (same time frame) gave rise to fishes of today