The Evolutionary Path To Vertebrates Animals (Metazoa) Fig 2.2
The Animals (Metazoa) Pathway to the Vertebrates http://tolweb.org/tree?group=Animals&contgroup=Eukaryotes
http://tolweb.org/tree?group=Bilateria&contgroup=Animals
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
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)
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)
bilateral symmetry
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)
blastocoelomate (pseudocoelomate) Pathway to the Vertebrates acoelomate blastocoelomate (pseudocoelomate) coelomate (eucoelomate)
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
Deuterstome Coelomates Pathway to the Vertebrates Deuterstome Coelomates radial, indeterminate cleavage blastopore becomes anus echinoderms, hemichordates, & chordates
Pathway to the Vertebrates Deuterostomes
Pathway to the Vertebrates Deuterostomes Echinodermata
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
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
Pathway to the Vertebrates Deuterstomes
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
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
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
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
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
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
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
Pathway to the Vertebrates The Chordates
= 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
bilaterally symmetrical Pathway to the Vertebrates Chordata Urochordata tunicate body plan bilaterally symmetrical use pharyngeal gill slits for suspension feeding
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
Pathway to the Vertebrates
So these things are really related to vertebrates?? Pathway to the Vertebrates So these things are really related to vertebrates?? look at metamorphosis
Chordata Urochordata reproduction & development most tunicates are hermaphroditic external fertilization typical results in free-swimming tadpole larva chordate characters much more apparent in larva
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
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)