Download Phylum Hemichordata

Phylum Hemichordata
(The ‘acorn worms’)
Also called acorn worms after the nut-shaped 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. Urochordata
Subphylum. Cephalochordata
Subphylum. 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)
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
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 Elasmobranchii- ancient “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 nowextinct 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)
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