1. The Evolutionary Path To Vertebrates
Animals (Metazoa)
Fig 2.2

2. The Animals (Metazoa) Pathway to the Vertebrates

4. present in eumetazoa (all others)
Pathway to the Vertebrates
A. True tissues absent:
Porifera (sponges)
B. True tissues present
present in eumetazoa (all others)
What is a tissue??
interconnected cells that perform a similar function

5. 1. Diploblastic (lack true mesoderm), radiate symmetry
Pathway to the Vertebrates
A. True tissues absent:
parazoa (sponges)
B. True tissues present
present in eumetazoa (all others)
1. Diploblastic (lack true mesoderm), radiate symmetry
Radiata (e.g. cnidarians: jellyfish, sea anenomes, etc)

7. 2. triploblastic (true mesoderm), bilateral symmetry
Pathway to the Vertebrates
A. True tissues absent:
parazoa (sponges)
B. True tissues present
present in eumetazoa (all others)
1. Diploblastic (lack true mesoderm), radiate symmetry
cnidarians and ctenophorans
2. triploblastic (true mesoderm), bilateral symmetry
remaining taxa (Bilateria)

8. bilateral symmetry

9. c. Coelomates (true coelom)
Pathway to the Vertebrates
A. True tissues absent:
parazoa (sponges)
B. True tissues present
present in eumetazoa (all others)
1. Diploblastic (lack true mesoderm), radiate symmetry
cnidarians and ctenophorans
2. triploblastic (true mesoderm), bilateral symmetry
remaining taxa
Acoelomate (without body cavity)
e.g., platyhelminthes
b. Blastocoelomate (blastocoel between gut and wall)
e.g., nematoda
c. Coelomates (true coelom)

10. blastocoelomate (pseudocoelomate)
Pathway to the Vertebrates
acoelomate
blastocoelomate (pseudocoelomate)
coelomate (eucoelomate)

11. Protostomes ii. Deuterostomes A. True tissues absent:
Pathway to the Vertebrates
A. True tissues absent:
parazoa (sponges)
B. True tissues present
present in eumetazoa (all others)
1. Diploblastic (lack true mesoderm), radiate symmetry
cnidarians and ctenophorans
2. triploblastic (true mesoderm), bilateral symmetry
remaining taxa
a. Acoelomate (without body cavity)
b. Blastocoelomate (blastocoel between gut and wall)
c. Coelomates (true coelom)
Protostomes
ii. Deuterostomes

12. Deuterstome Coelomates
Pathway to the Vertebrates
Deuterstome Coelomates
radial, indeterminate cleavage
blastopore becomes anus
echinoderms, hemichordates, & chordates

13. Pathway to the Vertebrates
Deuterostomes

14. Pathway to the Vertebrates
Deuterostomes
Echinodermata

15. exclusively marine (ubiquitous) large perivisceral coelom
Pathway to the Vertebrates
Deuterostomes
Echinodermata
around 7,000 species
exclusively marine (ubiquitous)
large perivisceral coelom
simple nervous system; no brain
no excretory system

16. Echinoderm Symmetry…bilateral?
Pathway to the Vertebrates
Deuterostomes
Echinoderm Symmetry…bilateral?
exhibit pentamerous radial symmetry as adults (larvae are bilateral)
pentamerous = body parts arranged in 5’s
radial = arranged around central axis

17. Pathway to the Vertebrates
Deuterstomes

18. 85 species, most in Class Enteropneusta = acorn worms or tongue worms
Pathway to the Vertebrates
Deuterostomes
Phylum Hemichordata
= “half chordate”
85 species, most in Class Enteropneusta
= acorn worms or tongue
worms
vermiform body with 3 body regions
proboscis
collar
where mouth is
trunk
benthic marine habitats as adults
share some characteristics with chordates

20. share some characteristics with chordates pharyngeal gill slits
Pathway to the Vertebrates
Deuterostomes
Phylum Hemichordata
= “half chordate”
share some characteristics
with chordates
pharyngeal gill slits
ciliated to facilitate water flow
dorsal (hollow) nerve chord
other characteristics:
complete digestive tract
dioecious with external fertilization

21. Phylum Chordata 4 chordate synapomorphies: 1. pharyngeal slits
Pathway to the Vertebrates
Phylum Chordata
4 chordate synapomorphies:
1. pharyngeal slits
2. dorsal hollow nerve chord
3. notochord
4. post-anal tail

22. Chordata 4 chordate synapomorphies: pharyngeal slits
Pathway to the Vertebrates
Chordata
4 chordate synapomorphies:
pharyngeal slits
perforated slitlike openings in pharyngeal cavity
2. dorsal hollow nerve chord
3. notochord
4. post-anal tail

23. Chordata 4 chordate synapomorphies: 2. dorsal hollow nerve chord
Pathway to the Vertebrates
Chordata
4 chordate synapomorphies:
1. pharyngeal slits
2. dorsal hollow nerve chord
3. notochord
4. post-anal tail

24. Chordata 4 chordate synapomorphies: 3. notochord
Pathway to the Vertebrates
Chordata
4 chordate synapomorphies:
1. pharyngeal slits
2. dorsal hollow nerve chord
3. notochord
dorsal, elastic rodlike structure
4. post-anal tail

25. Chordata 4 chordate synapomorphies: 4. post-anal tail
Pathway to the Vertebrates
Chordata
4 chordate synapomorphies:
1. pharyngeal slits
2. dorsal hollow nerve chord
3. notochord
dorsal, elastic rodlike structure
4. post-anal tail

26. Pathway to the Vertebrates
The Chordates

27. = tunicates, sea squirts 3,000 species solitary & colonial
Pathway to the Vertebrates
Chordata
Urochordata
= tunicates, sea squirts
3,000 species
solitary & colonial
all marine suspension feeders
superficially resemble poriferans

28. bilaterally symmetrical
Pathway to the Vertebrates
Chordata
Urochordata
tunicate body plan
bilaterally symmetrical
use pharyngeal gill slits for suspension feeding

29. use pharyngeal gill slits for suspension feeding
Pathway to the Vertebrates
Chordata
Urochordata
tunicate body plan
use pharyngeal gill slits for suspension feeding
water flows into mouth (incurrent siphon)
through gill slits
out excurrent siphon
gut is u-shaped
anus empties waste into excurrent siphon

30. Pathway to the Vertebrates

31. So these things are really related to vertebrates??
Pathway to the Vertebrates
So these things are really related to vertebrates??
look at metamorphosis

32. Chordata
Urochordata
reproduction & development
most tunicates are hermaphroditic
external fertilization typical
results in free-swimming tadpole larva
chordate characters much more apparent in larva

34. reproduction & development external fertilization typical
Pathway to the Vertebrates
Chordata
Urochordata
reproduction & development
external fertilization typical
results in free-swimming tadpole larva
larva settles on substrate, anterior end first
secretes adhesive
which triggers
irreversible
metamorphosis
tail absorption
begins within
minutes

35. viscera & siphons undergo 90o rotation brings organs to adult position
Pathway to the Vertebrates
viscera & siphons undergo 90o rotation
brings organs to adult position
pharynx enlarges for filtering
many larval organs lost (e.g, nervous system)