Phylum Hemichordata
(The ‘acorn worms’)





Also called acorn worms after the nutshaped proboscis (p482)
Worm-like benthic marine deuterotomes
Not ancestral to chordates, but a sister
group
Similar lifestyle to annelids, deposit feeder
Class Enteropneusta contains animals with
some chordate features:


Dorsal nerve cord
Gill slits in pharynx
The Chordates
(vertebrates and their relatives)
Chordate Subphyla
Phylum.
Chordata
Subphylum.
Subphylum.
Subphylum.
Urochordata
Cephalochordata
Vertebrata
Phylum Chordata
Includes a few ‘squishy’ animals and the vertebrates





4 Chordate Characteristics (all possess these at some
point during ontogeny- life cycle):
Notochord: a dorsal stiffening rod of cartilage, used
for endoskeletal support. Replaced by vertebrae
during development in vertebrates (including us…)
Dorsal hollow nerve cord: anterior end develops
into brain, this is the spinal cord in vertebrates
(encased in bone)
Pharyngeal gill slits: slits or grooves in pharynx,
which connect to outside in some, others (non-fish
vertebrates) form jaws, inner ear and bones, etc from
these pouches
Postanal tail: important ‘propellor,’ along with
myomeres, for bilateral animals in water. (only apes
have no tails as adults) (see fig 8-28)
Pikaia- oldest known chordate
(570mya) (see pic p 110
Subphylum Urochordata
The tunicates (‘squishy’ chordates)





~3000 species of sessile marine filter feeders
Adults have closed circulatory system, simple
ganglia for nervous system, and a large basket-like
filter feeding/respiratory structure. (see p 494)
Adults also called “sea squirts” after muscular
contraction that propels some away.
Larvae (p 496) have 4 chordate features. All are
lost in adulthood but the pharyngeal gill slits.
A population of paedomorphic (permanently
larval) sea squirts may be ancestral to vertebrates
(see p 500)
Urochordate larva:
(has four chordate features)
Incurrent
siphon
Excurrent siphon
and anus
Dorsal tubular
nerve cord
Notochord
Pharyngeal gill slits
Postanal Tail
Subphylum Cephalochordata
The lancelets (‘worm fish’)





Bilaterally symmetrical small marine filter-feeding
chordates, similar in structure to tunicate larvae
(see p 497) Adult has all chordate features,
including tail with fin. Pharyngeal gill bars
covered with cilia and mucus (like clam); used to
catch food particles.
Constant flow of water through body from oral
opening to atriopore.
Can swim, but spends most time in sediment.
Muscle groups called myomeres arranged as in
fish.
Branchiostoma is common N.A. genus, very
similar to earliest known chordate fossil genus
Pikaia (p 500)
Cephalochordata
Notochord
Nerve cord
Tail
Anus
Mouth
Pharyngeal gill slits
Atriopore
Subphylum Vertebrata
All animals with vertebrae (includes humans)







poor fossil history of very early proto-chordates
means that we don’t yet know which group gave
rise to the vertebrates(urochordates, cephalo’s,
etc)
Of early vertebrates, though, the fossil record is
not bad. These features are unique to
vertebrates:
Paired appendages as seen in early fishes (pelvic
and pectoral fins became front and back legs)
Endoskeleton: first mesodermal bone!
Bony vertebrae replaced notochord; enclosing
spinal cord and allowing attachment of limb
bones
Cranium (skull) formed to protect brain
Jaws with teeth for eating larger items
The First Fishes
(condensed evolution of the first vertebrates)




First vertebrates in fossil record are ostracoderm
fishes, which lack many of the previous features
(especially jaws), but are certainly vertebrates (see
all forms, page 502)
These early fish lacked internal bones, instead had
dermal bony plates.
Osteostracan ostracoderms (with pectoral fins) may
have evolved into first gnathostomes, which
appeared much later (during Devonian period)
See p504, Acanthodian fish with scales, bony
jaws and fins; is likely ancestor of all modern
gnathostome (jawed) fishes
Modern Fishes
Agnathans, sharks and rays, the boney fishes…



Cold-blooded (ectothermic) aquatic vertebrates
with gills and fins
~25,000 species; more than all other vertebrates
combined. Range in size from less than 1cm to 15m
Superclass Agnatha


Class Myxini (hagfishes): marine scavenging jawless
fish with cartilage instead of bones. Mucus produced
in vast quantities for defense.
Class Cephalaspidomorpha (lampreys): aquatic
ectoparasites of fish with cartilage in place of bone.
More Modern Fishes (sharks and relatives)





Class Chondrichthyes, subclass Elasmobranchiiancient “cartilage fishes,” sharks, rays~ 850 species.
Skeleton of cartilage, but boney teeth, jaws and
vertebrae
Large liver used for blood filtration and buoyancy
(instead of having an air bladder)
Intestine with spiral valve for increased absorption.
Senses: no hearing; mediocre eyesight; awesome
smell-sense (chemoreception); pressure/disturbance
sense via lateral line system; bioelectric sense via
hundreds of tiny ampullae of Lorenzini located in
the skin of sharks and rays head.
The Boney Fishes- Osteichthyes
all the other fishes
Class Sarcopterygii- Lobe-finned fishes, including
lungfishes and coelacanth fish
 Class Actinopterygii- the Ray-finned fishes: all the
fish you eat, catch or keep as pets.. ~23,000
species, arose in the Silurian soon after the
cartilaginous fish.
 Bony skeleton and fin-rays
 Air bladder used for buoyancy and respiration
 Gills release excess salt and are covered by
operculum
 Lateral line system as in sharks, no bioelectric
sense

Class Amphibia
Frogs, salamanders and how we got there…
During the Devonian, a very hot and dry period in
which many fishes lived in muddy waters with low O2,
some populations of Sarcopterygian fish developed
lungs and limb bones…
 When waters dried up, some populations survived
drought by breathing air and eventually hunting on
land. These first Tetrapods (terrestrial vertebrates
with 4 feet) were the first amphibians (both lives)
 See ‘missing links’ Eusthenopteron and Ichthyostega
 Features: scales, lungs, tail fin, limbs with humerus
radius & ulna, lateral line system, forward-facing
eyes, tear ducts, others…

Ichthyostega (see on p 541)
Modern Amphibians
Remnants of a grand old group…

Class Lissamphibia (frogs, salamanders and
caecilians)- all must reproduce in water, have no
claws and moist skin (no scales)



Order Anura- Frogs and Toads, ~3500 species: most
derived group; evolved for saltation (jumping); Toads
are most terrestrial amphibians. Complex vocalizations
Order Caudata- Salamanders, ~350 species: All have
tail, complex breeding behavior, very cold tolerant
Order Gymnophiona- Caecilians, legless
salamanders with ringed body. Few species, all
tropical, most are subterranean worm eaters
The Amniotes
(all vertebrates ‘above’ amphibians)
All land-based vertebrates that do not reproduce in
water are amniotes (reptiles, birds & mammals)
 The major step that allowed reptiles, mammals and
birds to evolve was the amniotic egg: the single
most important vertebrate evolutionary event.
 The amniotic egg is a self-contained pond (amnion),
buffet dinner (yolk), and scuba tank (allantois) in
one; the young emerge large, fat and nearly adult
(see page 559). This allowed vertebrates to colonize
arid (dry) areas.
 The first amniotes to evolve were reptiles.

See amniotic egg
Fig 28-8, p 564 Know amnion,
allantois, yolk and chorion
The Reptilian skull (or skulls)
The first reptiles had anapsid skulls (~300 mya).
They were the turtles, and some now-extinct forms.
 Later reptiles evolved synapsid skulls that had one
hole in the temporal region. This allowed for more jaw
muscle attachment, and better biting/chewing ability.
The only living reptiles with synapsid skulls are today
called mammals! (yes, that’s us…)
 The best type of reptile skull was diapsid, though; with
two temporal openings. This skull is more flexible,
allows for stronger jaws, and better protected brain.
 Two branches of diapsids:
 Archosaurs- crocodylians, dinosaurs and birds
 Lepidosaurs- lizards, snakes, pterosaurs & other
extinct groups

Major reptile groups
(see skulls, p 562)
Anapsid
 Synapsid
 Diapsid

Why Reptiles are better
(than amphibians)





Amniotic egg allowed world domination (really!)
Better egg was associated with internal
fertilization
Faster metabolism allowed for evolution of
bigger better brain to process more information
from better eyes, ears, and nose.
More flexible/efficient limbs and joints with new
carpals and tarsals (first reptiles were
small/lanky and could climb trees! Early
amphibians could not…)
Scales keep body from drying out and help
protect it
Order Testudines
the turtles





The only surviving members of the most ancient
group of reptiles, the anapsids
No teeth, horny beak instead
All senses mediocre, but defense is great- the
shell! Made of fused vertebrae, ribs and skin
bones called scutes, the shell grows with the
body
Most turtles are herbivores, but snapping turtles
and soft-shelled turtles are carnivorous
Longest-lived vertebrates… some ~200 years
Order Crocodylia
crocodiles, alligators and the garial







Ancient line of reptiles, with similar skulls to
dinosaurs and birds (archosaurs)
22 modern species, hundreds of extinct species
Have good hearing, eyesight and sense of smell.
Also have bioelectric sense like sharks!
All are fully carnivorous awesome predators…
Engage in complex parental care (like dinos and
birds), and use various vocalizations
Awesome bite force due to gigantic jaw muscles
and large pterygoid bones (3000 lbs/sq. inch)
We could go on forever! (I love the ugly
buggers)
Order Squamata
(lizards, snakes and amphisbaenians)
These are lepidosaurs (the other group of diapsids)
 All have lightweight efficient skulls with powerful
muscles.
 Suborder Sauria- lizards. Highly derived small
diapsid reptiles. Good hearing and eyesight. Most are
terrestrial insect eaters. Lots of sexual dimorphism
and mate-selection behaviors. Largest is “Komodo
dragon”
 Suborder Serpentes- snakes! Derived from early
lizards, but not as old (late Jurassic period). Poor
hearing (no external ear opening), but great sense of
smell (Jacobson’s organ). Very secretive animals that
commonly use burrowing and camouflage for defense,
as well as toxins (but most are non-venomous).

Class Aves- the birds
(or Order Aves within Class Reptilia)
Super-derived archosaurs (diapsids) directly descended
from small raptorial dinosaurs.
 More derived (changed) from original reptile stock than
are the mammals
 Lightweight skulls with much flexibility, large brains and
no teeth (beak instead).
 endothermic (warm-blooded) due to high metabolic
rate. Can live in very cold climates!
 Body covered in modified scales known as feathers
 Feathers came before flight! – original use for insulation
(warmer than hair/fur). Evidence several species of
small flightless dinos from the fossil record which are
covered in feathers! (cool…)

Birds continued…
More evidence that birds are dinos, both
have:
 hollow bones, scales and feathers, beaks,
the “wish bone,” special wrist bones, keeled
sternum, feet & claws, etc…
 Finest respiratory system on earth. Have one
large lung and many air sacs in various
locations. Get oxygen while inhaling and
exhaling (fresh air passes through lung in
both directions)
 Highly evolved social behaviors like
migration, parental care, complex
vocalization and mimicry, mate selection…
 Large number of species (~9000) for a huge
variety of habitats/food
preferences/lifestyles

See avian respiratory figure
P 593, fig 29-12
Class Mammalia
You know! People, dogs, cats, dolphins, etc…
Mammals are derived from Permian-age
synapsid reptiles called cynodonts.
 The often-discussed mammalian features
are: mammary glands, hair and/or fur,
heterodont teeth, endothermy, and a big
brain with thick neocortex
 Mammals also have the finest combination
of sensory systems, and some of the
highest metabolic rates (shrews) and
nervous reflex speeds.
 Social mammals (whales & dolphins, apes,
dogs) are most intelligent animals on the
planet (we think…)

More Mammals…
See Modifications of the teeth for various feeding
strategies (page 618)
 See that mammals which eat more plant material have
longer digestive tracts and larger cecae. (p 619)
 Order Monotremata- egg layers (like platypus)
 Order Marsupialia- viviparous pouched animals which
used to be far more common (during Cretaceous and
early Eocene) than the placentals
 Infraclass Eutheria- the placental mammals
 Orders to know: Insectivora, Chiroptera,
Primates, Lagomorpha, Rodentia, Cetacea,
Carnivora, Perissodactyla, Artiodactyla

See mammalian embryonic
condition
Fig 8-22, p 173
Vertebrate Reproduction is Sexual





Most species (all dioecious) copulate
All produce gametes (eggs & sperm) by
meiosis. Gametes are haploid.
Haploid gametes fuse after or during
copulation – fertilization.
Fused gametes called a zygote (diploid)
Zygote develops into new genetically
unique individual. (p. 138)
See vertebrate life cycle
(mating rats pic)
Fig 7-2, p 138
Embryology
(study of the embryo’s development)





Within minutes or hours of fertilization, the zygote
will begin cleavage (mitotic divisions)
Zygote divides until its called a blastula
Hollow blastula will develop a depression on one
side that grows. This is now a gastrula.
After gastrulation, cells become differentiated
into ectodermal, mesodermal or endodermal
Differentiation of tissues continues due to
expression of genes… (see figs 8-2 and 8-6)
Genetics Basics
(Remember meiosis?)






Every human body cell contains 46 chromosomes, or
23 pairs of homologous chromosomes.
Each person gets ½ their chromosomes (23) from
each parent’s gamete. Zygote then has 46.
A homologous pair look alike (usually) and carry
information about the same genes.
So, each cell has 2 copies of every gene.
Different forms of a gene are called alleles
Interaction between alleles determines the gene
expression (phenotype)
Sex determination
(see fig. 5-3)





The sex chromosomes are #23 (last)
Men- XY Women- XX
Egg cell (female gamete) can only provide
an X chromosome (that’s all Mom’s got!!)
Dad’s got an X & Y, so can donate either
of these (not both!) in his sperm.
So, the sperm cell will contain (for #23)
an X or a Y chromosome, determining the
gender of the offspring.
Allelic Interactions





Most genes exist as two alleles; dominant or
recessive
So, for each gene, a person will have two dominant
alleles, one dominant & one recessive allele or two
recessive alleles.
Alleles same: homozygous (2 dom or 2 rec)
Alleles different: heterozygous (1 of each)
In heterozygous condition, dominant allele will
usually be expressed.
In genetic diseases, the abnormal (disease) form of
the gene is usually the recessive allele
Example…





Black feathers in a chicken species are
dominant over white feathers (same gene)
Dominant= B Recessive= b
What color will the feathers of a ‘BB’
chicken be?
What color will the feathers of a ‘Bb’
chicken be?
What color will the feathers of a ‘bb’
chicken be?
Testcross





In order to determine the interaction of
dominant and recessive alleles, this is done.
Parental generation (both homozygous)
BB X bb (genotypes, what are phenotypes?)
F1 generation (offspring from P generation)
all Bb – under normal conditions, all black
F2 generation (offspring from F1 generation)
1 BB; 2 Bb; 1bb
See monohybrid cross punnett square on
board… (& see p 81)
Other genetics terms…


Incomplete dominance- condition in which
the heterozygote expresses ‘in between’ traits
(see blue chicken, p. 83)
Sex-linked inheritance- genes carried on the
X sex chromosome, which men are more likely
to express because they have only one of these.
If male possesses the defective (recessive)
allele, he will express color blindness, for
example. Women may be carriers for these
diseases (having no expression) See fig. 5-7