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KINGDOM ANIMALIA
Phylum Chordata
Chordate Relatives
Common ancestry
revealed by dorsal
nerve tube and
pharyngeal gill slits
Gill slits form
(throat pocketings)
at some time during
development; used
for feeding or gas
exchange
Phylum Hemichordata
85 species of acorn or
tongue worms
Ciliated mucuscovered proboscis,
resembles acorn or
tongue
Burrow in sediment
and feed on sediment
or filter feed
Elongated trunk with
pharyngeal openings
Single dorsal nerve
cord
Phylum Chordata
Three subphyla unified by
having a notochord at
some point in life cycle
and metameric tail
Notochord = densely
packed muscle fibrils
enclosed by sheath in rod
shape; provides skeletal
support
Metameric tail = repetition
of similar segments;
extends beyond anus
Subphylum Urochordata
3000 species of tunicates or sea squirts
Earliest derivative of chordate line
Adults bear no resemblance to other
chordates, but larval features indicate nerve
cord and notochord
These disappear during metamorphosis
Only chordate feature remaining = gill slits
(filter feed)
Subphylum Urochordata
Soft-bodied marine filter feeders
Wide variety of sizes, shapes, and
colonial structure
All have outer covering (tunic) containing
tunicin (cellulose-like) and in/ex-current
siphons
Subphylum
Cephalochordata
Small group of 23 species
of lancelets or amphioxus
Fish-like and free
swimming, also burrow in
sand with only head
protruding
Unique feeding apparatus
for suspension feeding
(buccal cirri/gill slits)
Resemble vertebrates
more; may represent living
descendants of vertebrates
Subphylum Vertebrata
Around 49,000 species
of vertebrates
Significant not in size
or age of group, but
its morphological
diversity, structural
complexity, and
trophic dominance
Three novelties bind
all vertebrates
Subphylum Vertebrata
3 Vertebrate Novelties
1. Neural crest tissue = specialized kind of
ectoderm that gives rise to nervous
system, retina, gill cartilage, and
pigment cells
2. Enlargement of anterior end of neural
tube to form the brain
3. Endoskeleton = backbone composed of
vertebrae (bony/cartilaginous segments
replace notochord during development),
cranium (bony/cartilaginous housing for
brain), paired pectoral and pelvic
appendages
Subphylum Vertebrata
All are bilaterally symmetrical with regional
differentiation
Head region = houses sensory organs, brain,
anterior opening to digestive tract
Trunk region = body cavities that house viscera
Tail or caudal region = lacks viscera, but has
muscles and skeleton (function in locomotion,
reduced, or specialized)
Subphylum Vertebrata
Metamerism (serial repetition of
body parts) limited to trunk
muscles, skeleton (vertebrae and
ribs), and the nerves associated
with trunk
All have gills at some point in life
cycle (breathing organs or
transient developmental
structures)
Closed circulatory system =
arteries move blood to periphery
from multi-chambered heart,
veins move blood from periphery
to heart, capillaries
Myomeres associated with
endoskeleton
Vertebrate Classes
Vertebrate Diversity
Major evolutionary innovations among
vertebrate groups fall into four categories:
1.
2.
3.
4.
Musculoskeletal system
Nervous system
Respiratory/circulation systems
Nature of the egg
Musculoskeletal system
Most primitive in jawless
vertebrates (hagfish, lampreys),
have reduced braincase and
cartilaginous gill-arch supports
Hagfish = only notochord
Lamprey = notochord strengthened
by addition of small arches of
cartilage in anterior trunk segments
and small blocks of cartilage
posteriorly--These are evolutionary
precursors to vertebrae!
Musculoskeletal system
All other vertebrates:
– replacement of notochord
with bony* vertebrae-articulate, protective
housing for nerve cord
– development of
pectoral/pelvic
appendages (from fins to
limbs)
– appearance of jaws
associated with braincase
*cartilage in sharks/rays-descended
from bony ancestors
Nervous System
Increased structural complexity allowed an
elaborate nervous system to evolve
Cephalization: elaboration of the anterior
end of spinal cord to form hollow brain and
sensory organs (protected by skull)
Peripheral nervous system: paired nerves in
every body segment (relay brain’s messages
to periphery)
Nervous System
Autonomic nervous system: function
automatically without voluntary control
by brain
– Sympathetic: increases activity, slow
digestion
– Parasympathetic: decreases activity,
stimulate digestion
– This complementary system best
developed in mammals so they can
maintain metabolic activity while still
able to respond to external conditions
Respiratory/Circulation
Respiration:
– Vertebrates require more oxygen than inverts,
birds/mammals = highest demands (endothermic)
– Soft skin, moist environment (eel, amphibian) = gas
exchange across skin in addition to respiratory
organ
– Gills or lungs = derived from the pharynx
– Water pumped across gills, get gas exchange
– Air breathed into lung, gas exchange across
epithelial lining
– Birds also have air sacs extending from lungs into
many parts of body
– Mammals have diaphragm to forcefully pull air
in/expel air out
Respiratory/Circulation
Circulation:
– Allied with respiratory system:
transports oxygen, nutrients, and
water to cells and removes
wastes/carbon dioxide
– All systems closed: heart, arteries,
veins, capillaries
– In gilled, 2-chamber heart: one atrium,
one ventricle, blood enters heart via
veins, leaves via aortic arches in gills
(gas exchange), blood proceeds to rest
of body
– In amphibians, aortic arches are
reduced and modified into vessels in
order to pass blood from lungs to 3chambered heart (atrium separated by
septum, one ventricle)
Respiratory/Circulation
Circulation:
– In snakes and lizards, ventricle
also has septum (incomplete 4chambers)
– In birds and mammals,
complete separation of
oxygenated/deoxygenated
blood, 4-chambered heart,
efficient system with no mixing
gives greater blood volume and
higher blood pressure (needed
for metabolic requirements)
– Kidneys = separate food/water
from excess salt/waste in blood
The Egg
Eggs enclosed by plasma
membrane internally and vitelline
membrane externally
Fish and amphibian eggs pass
down oviduct where chitinous
chorion or gelatinous proteinpolysaccharide material added
(anamniote egg = no amniotic
membrane)
External fertilization; moist climate
to prevent desiccation
The Egg
Evolution of amniote egg:
equipped with extra membrane
layers of protection (amnion, yolk
sac, chorion, allantois) as well as a
leathery/calcareous shell
In reptiles and mammals
(monotremes); fertilization
internal; subject to predation
Marsupials and placental
mammals retain young internally
(helps young develop to an
advanced stage before born)