Download 34.4: Gnathostomes are vertebrates that have jaws - APBio10-11

INVERTEBRATES AND VERTEBRATES (ANIMALS)
3.1 ANIMALS ARE MULTI-CELLULAR , HETEROTROPHIC EUKARYOTES WITH TISSUES
THAT DEVELOP FROM EMBRYONIC LAYERS
NUTRITIONAL MODE
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Animals cannot create their own organic molecules unlike plants, so they ingest them
Animals do not feed by absorption like fungi, they digest them with enzymes
CELL STRUCTURE AND SPECIALIZATION
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Animals are multicellular, but lack structural support of fungi and plants
o Animal cells are held together by collagen
Animals have specialized cells specific to animals: muscles and nerve
o Muscle tissue is responsible for moving the body
o Nerve cells conduct nerve impulses
REPRODUCTION AND DEVELOPMENT
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Most animals reproduce sexually and diploid stage dominates the life cycle
o Usually flagellated sperm fertilizes large, nonmotile egg
o Insert chapter 47
o Sometimes animals are a larva:
 Sexually immature form of an animal that is morphologically distinct from the adult,
usually eats different food and may even have different habitats
o Metamorphosis: developmental transformation that turns the animal into a juvenile, which
resembles an adult but is not yet sexually mature
Although adult animals very widely, the underlying genetic network that controls animal development is
similar
o Genes that regulate expression: homeoboxes
o All have hox genes that control development of animal embryos
 Sponges have hox, insects have hox—who doesn’t have hox?!
 Hox regulate patterning of anterior-posterior development, formation of
structures important to the animal
32.2: THE HISTORY OF ANIMALS SPANS MORE THAN HALF A BILLION YEARS
NEOPROTEROZOIC ERA (I BILL – 542 MILL YEARS AGO)
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Ediacaraon biota: early group of multicellular eukaryotes
o Soft-bodied, found in the Ediacara Hills of Australia
Early animals
o Found in China, basic structural organization of present-day animal embyos
PALEOZOIC ERA (542 MILL – 251 MILL YEARS AGO)
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Cambrian explosion: animal diversification acceleration
o After the Cambrian explosion, more and more strata are able to be identified
o Causes?
 Predator-prey relationships (creation of defenses and locomotion)
 Rise in atmospheric oxygen (higher metabolic rates and larger body sizes thrive)
 Evolution of the Hox gene complex
Ordovician, Silurian and Devonian
o Animal diversity continued to increase, but it was punctuated by episodes of mass extinctions
o Vertebrates (fishes) emerged as the top predators of the marine food web
o Arthropods began to adapt terrestrial habits (millipedes and centipede)
o Fern galls suggests insects and plants were influencing each other’s evolution by that time
Vertebrates made the transition to land 360 mill years ago and diversified
o Amphibians and amniotes
MESOZOIC ERA (251 – 65.5 MILL YEARS AGO)
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Old phyla spread to new ecological habitats (coral reefs)
Reptiles returned to water and succeeded as large aquatic predators
Tetrapods led to the origins of wings
Smalls dinosaurs emerged
First mammals (tiny nocturnal insect-eaters) appeared
Plant diversification
CENOZOIC ERA (65.5 MILL YEARS AGO – PRESENT)
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Mass extinctions of terrestrial and marine animals caused the new era
Dinosaurs disappeared
Rise of large mammalian herbivores and predators
Global climate cooled, changing animal lineages
32.4: NEW VIEWS OF ANIMAL PHYLOGENY ARE EMERGING FROM MOLECULAR
DATA
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There’s lots of debate over how phylum relate to each other
POINTS OF AGREEMENT
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All animals share a common ancestor
a. If we could trace all extant and extinct animal lineages, they’d converge on a common ancestor
Sponges are basal animals
a. They’re a paraphyletic, falling into at least two phyla
Eumetazoa is a clade of animals with true tissues
a. Eumetazoans: true animals, all animals except sponges—diploblastic and generally feature radial
symmetry
Most animal phyla belong to the clade Bilateria
a. Bilateral symmetry and presence of three-germ layers are shared derived characters that help
define clade Bilateria. Bilaterians: are the members of this clade, and the Cambrian explosion
helped these guys out
Chordates and some other phyla belong to the clade Deuterostomia
a. Deuterostome: mode of animal development and members of a clade that includes vertebrates
and chordates
PROGRESS IN RESOLVING BILATERIAN RELATIONSHIPS
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In the diagram shown above, we divide the bilaterians into two clades: deuterosomes and protostomes.
What if they aren’t really different?
Ecdysozoans and lophotrochozoans: animal phylum in deuterosomes
o Ecdysozoan: characteristics shown by nematodes, arthropods and ecdysozoans, secrete
exoskeleton (ecdysis)
o Lophotrochozoans: develop a lophophore, a crown of tentacles that function in feeding
 Others go through a developmental phase called trochophore larva
33: A OVERVIEW
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Invertebrates: animals without a backbone, account for 95% of known animal species
33.1: SPONGES: CALCAREA AND SILICEA
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Sedentary, mistaken for plants by the Greek
Large range in size
Suspension feeders: capture food particles suspended in the water that passes through t heir body
Spongocoel: the central cavity where the water is drawn into
Osculum: the larger opening of the sponge where water is expelled
Basal animals, represent a lineage that originates near the root of the tree of animals
Lack true tissues (groups of similar cells that act as a functional unit and are isolated from other tissues by
membranous layers
Choanocytes: collar cells, lining the interior of the spongocoel
Mesohyl: gelatinous region between two layers of cells
Amoebocytes: cells that move around, take food from water and from choanocytes, digest it and carry
nutrients to other cells, manufacture touch skeletal fibers
Hermaphrodites: each individual functions as both male and female by producing both sperm and eggs
o Gametes come from choanocytes or amoebocytes
o Eggs reside in the mesohyl, but sperm are carried out of the sponge by water current
o Fertilization occurs in the mesohyl, where zygotes develop into flagellated larvae that disperse
Produce a variety of antibiotics and other defensive compounds
33.2: CNIDARIA
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One of the oldest of the Eumetazoas (animals with true tissues)
Diversified into a wide range of sessile and motile forms, including hydras, corals and jellyfish
Gastrovascular cavity: basic body plan, sac with central digestive compartment—single opening functions
as a moth and an anus
o Polyps: cylindrical forms that adhere to substrate by aboral end of their body (end opp the
mouth) and extend their tentacles, waiting for prey
o Medusa: flattened, mouth-down version of polyp, moves freely in the water by a combination of
passive drifting and contractions of its bell-shaped body
 Include free-swimming jellies
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Carnivores that often use their tentacles arranged in a ring around their mouth to capture prey and push
food into the gastrovascular cavity
o Undigested remains are expelled through the mouth/anus
o Cnidocytes: cells unique to cnidarians that function in defense and prey capture, cells are on
their tentacles
Contain capsule-like organelles that are capable of exploding outward
Nematocysts: specialized cnidae, contain a stinging thread that can penetrate the body wall of the prey
Contractile tissues and nerves occur in their simplist forms in cnidarians
o Epidermis and gastrodermis have bundles of microfilaments arranged into contractile fibers
o Gastrovascular cavity acts as hydrostatic skeleton
 When mouth is closed, V of cavity is fixed and contraction of cells cause animal to
change shape
o Movements coordinated by nerve net, but Cnidarians have no brain and no central nerve net
o They can respond to stimuli from all directions b/c of t heir sensory structures distributed radially
around the body
HYDROZOANS
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Alternate between polyp and medusa forms
o Polyp stage: colony of interconnected polyps is more conspicuous than medusa
 Hydras only exist in polyp form, reproduces by budding in favorable conditions
SCYPHOZOANS
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Medusa is generally predominant stage in the life cycle
o Live among plankton as jellies
o Most coastal types go through a stage as small polyps during their life cycle
o Oceanic types lack a polyp stage
CUBOZOANS
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“cube animals”
o Have a box-shaped medusa stage
o Have complex eyes embedded in the fringe of their medusa
o Comparatively strong swimmers, less likely to be stranded on shore
o Live in tropical oceans, equipped with toxic cnidocytes
 Ex: sea wasp (Chironex fleckeri), sting causes respiratory failure
ANTHOZOANS
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Sea anemones and corals (“flower animals”)
Only live as polyps
Corals live in solitary/colonial forms, many species create hard external skeleton of calcium carbonate
Each polyp generation builds on the skeletal remains of the earlier generation
Coral reefs provide habitat for many other species
33.3: LOPHOTROCHOZOANS , A CLADE IDENTIFIED BY MOLECULAR DATA , HAVE THE
WIDEST RANGE OF ANIMAL BODY FORMS
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Majority of animal species belong to Bilateria bilateral symmetry and tripoblastic development,
coelomates
Lophotrochozoas develop from a structure called a lophophore, a crown of ciliated tentacles that
functions in feeding OR from a stage called the trochophore larva OR neither
FLATWORMS
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Live in marine, freshwater, and damp terrestrial habitats
Include many parasitic species (flukes and tapeworms)
Flatworm body
o Undergo tripoblastic development, but are acoelomates (lack body cavity)
o Flat shape places all their cells close to water in the surrounding environment/gut
 Gas exchange occurs by diffusion across a body surface
 Protonephridia: networks of tubules with ciliated structures called flame bulbs that pull
fluid through branched ducts opening to the outside
 most flatworms have a gastrovascular cavity with only one opening
 lack circulatory system
o divided into four classes
TURBELLARIANS
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Nearly all free-living and mostly marine
Planarians: best known freshwater turbellarians from Dugesia
o Live in unpolluted ponds, prey on smaller animals/feed on dead animals
o Move by using cilia on their ventral surface
o Head is equipped w/ pair of light sensitive eyespots and lateral flaps that function mainly to
detect specific chemicals
o Some reproduce asexually from fission, others reproduce through sexual reproduction
(hermaphrodites)
MONOGENEANS AND TREMATODES
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Live as parasites, many have suckers that attach to internal organs/outer surfaces of a host animal
Though covering helps protect parasites within their hosts
Reproductive organs occupy almost the entire inside of the worms (EW EW EW EW)
Most trematodes have complicated live cycles w/ alternating sexual and asexual stages
o Require an intermediate host in which larvae develop before infecting the final host
o They have really badass defense systems that can mimic fool host systems for a really long time
Most monogeneans are external parasites of fish
1. Mature flukes live in the blood vessels of the human intestine
2. Blood flukes reproduce sexually in the human host. Fertilized
eggs exit the host in feces.
3. If the feces reach water, the eggs develop into ciliated larvae.
The larvae infect snails (intermediate hosts)
4. Asexual reproduction within the snail results in another type
of motile larva, which leaves the snail host
5. These larvae penetrate the skin/blood vessels of humans
working in fields and the cycle starts again…
TAPEWORMS (CESTODA)
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Parasitic, usually live inside humans
Anterior end (scolex) is armed with suckers and hooks that the worm uses to attach itself to the intestinal
lining of the host
Lack mouth/gastrovascular cavity, absorb nutrients released by digestion in the host’s intestine, occurs
across body surface
Posterior to scolex is a long ribbon of units called proglottids, sax of sex organs
o After sexual reproduction, proglottids are loaded with thousands of fertilized eggs are released
from the posterior end and leave the host in feces
o Infected feces contaminate water, which are fed to intermediate hosts and tapeworm eggs
develop into larvae that encyst in the muscles
o Human acquires larvae by eating undercooked meat and worms develop into mature adults
within human
ROTIFERS
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Tiny animals that inhabit freshwater, marine, damp soil habitats – usually smaller than protists, but have
multicellular and specialized organ systems
Alimentary canal: digestive tube with a separate mouth and anus
Internal organs lie within pseudocoelom, a body cavity that is not completely lined by a mesoderm – fluid
serves as a hydrostatic skeleton
Rotifer means “wheel bearer”, reference to crown of cilia that draws a vortex of water into the mouth
Reproduction
o Parthenogenesis: females that produce more females from unfertilized eggs
o Two types of eggs that develop parthenogenesis
o Forms females while the other type develops into simplified males that can’t feed themselves,
survive only long enough to fertilize eggs
LOPHOPHORATES: ECTOPROCTS AND BRACHIOPODS
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Have a lophophore, a crown of ciliated tentacles that surround the mouth that trap food particles
U-shaped alimentary canal and absence of a distinct head
Have a true coelom that is completely lined by a mesoderm
Ectoprocts: colonial animals that superficially resemble clumps of moss
o Exoskeleton: external skeleton that encases the colony, studded with pores through which
lophophores extend
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o Live in the sea and lakes, sessile
Brachiopods: Lamp shells, resemble clams
o All brachiopods are marine, most live attached to the seafloor by a stalk
MOLLUSCS
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Includes snails, slugs, oysters, clams, octopi and squids
Marine, some inhabit fresh water and land
Soft-bodied animals, but most secrete hard protective shells made of calcium carbonate
Molluscs are coelomates, and their bodies have three main part
o Foot: used for movement
o Visceral mass: containing most of the internal organs
o Mantle: fold of tissue that drapes over the visceral mass and secretes an shell
o Mantle cavity: houses the gills, anus and excretory pores
o Radula: straplike rasping organ that grasps food
Most have separate sexes and their gonads are located in the visceral mass
o Snails are usually hermaphrodites
o Life cycle usually includes a ciliated larval stage (trochophore)
Classes include: Bivalvia, Gastropoda, Polyplacophora and Cephalopoda
CHITONS
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Usually have a large oval-shaped body and a shall divided into 8 dorsal plates
You can find these clinging to rocks along the shore during low tide
Uses its foot to creep slowly over the rock surface
Use their radula to scrape algae off the rock surface
GASTROPODS
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Most are marine, but some are freshwater
Most have adapted to live on land, like snails and slugs
Torsion: as a gastropod embryo develops, its visceral mass rotates up to 180 deg causing the animals’
anus and mantle cavity to wind up above its head… wtf
Most have a single, spiraled shell into which the animal can retreat when it’s threatened
o Many have a distinct head w/ eyes at the tips of tentacles
o Move slowly by a rippling motion oof their foot/cilia, leaving a trail of slime
o Use their radula to grace on algae/plants
 Some are predators radula can bore holes through the shells of other animals
o Terrestrial snails lack the gills typical of most aquatic gastropods, instead their mantle cavity
functions as a lung
BIVALVES
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Clams, oysters, mussels and scallops
Have shell divided into two halves, hinged at the middle dorsal line and powerful adductor muscles draw
them tightly together to protect body
Have no distinct head and radula has been lost
Some have eyes/sensory tentacles
Mantle cavity
o Contains gills that are used for gas exchange/feeding
o Most are suspension feeders—trap food in their gills
Most are sessile
CEPHALOPODS
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Active predators – use their tentacles to grasp prey and bite into them with beak-like jaws
The foot of the cephalopod has become modified into a muscular excurrent siphon and a part of the
tentacles
Squids and octopi move by drawing water into their mantle cavity and firing a jet of water through the
excurrent siphon
Mantle covers the visceral mass of cephalopods, but the shell is reduced and internal (squids and cuttle
fish)/nonexistent
Only molluscs with a closed circulatory system, well-developed sense organs and complex brain
Amnonites: shelled cephalopods were FUCKING HUGE (think truck tires)
Most species are smaller—notable exceptions include the giant squid that uses its tentacles to kill its prey
ANNELIDS
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“little rings”, referring to the annelid body’s resemblance to a series of fused rings
Segmented worms that live in the sea, most freshwater habitats and in damp soil
Coelomates, range in length
Can be divided into three classes: Oligochatea, Polychaeta and Hiudinea
OLIGOCHAETES
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Named for their sparse chaetae, or bristles made of chitin
Includes earthworms, who eat their way through the soil, extracting nutrients as the soil passes t hrough
the alimentary canal
Hermaphrodites, cross-fertilize
o Received sperm is stored in an organ called the clitellum, secretes a cocoon
o Some can reproduce asexually by fragmentation/regeneration
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Each segment is surrounded by longitudinal muscle, which is surrounded by circular muscle
Coelom: is partitioned by septa
Metanephridium: each segment contains a pair of excretory tubes which ciliated funnel-shaped openings
called nephrostomes; remove wastes from blood
Chaetae: each segment has four pairs of chaetae, bristles that provide traction for burrowing
Cerebral ganglia: nervous system; ring of nerves around pharynx connects to subphryngeal ganglion
Ventral nerve cords w/ segmented ganglia: nerve cords penegrate septa and run the length of the
animal, as do digestive tract and long blood vessels
Closed circulatory system
POLYCHAETES
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Paddle-like/ridge-like structures called “parapodia” that function in locomotion
o Each has numerous chaetae, so polychaees usually have many more chaetae/seg than do
oligochaetes
Make up a large/diverse class, most are marine
LEECHES
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Mostly inhabit fresh water, some are terrestrial
Suck blood by attaching temporarily to other animals
o Host is usually oblivious b/c the leech secretes an anesthetic
o Secretes hirudin, which keeps the blood of the host from clumping
o Leech sucks as much blood as it can hold
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Until this century, leeches were used for bloodletting
Now they’re used to drawing blood that accumulates in tissues following certain injuries/surgeries
33.4: ECDYSOZOANS ARE THE MOST SPECIES-RICH ANIMAL GROUP
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Cuticle: tough external coat that is shed in this group
Molting: ecdysis
NEMATODES
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Ubiquitous animals, roundworms, found in most aquatic habitats
Do not have segmented bodies, covered by a tough cuticle that is shed as the worm grows
Have alimentary canal, but no circulatory system, nutrients are transported via fluid in the pseudocoelom,
body wall muscles are longitudinal
Reproduce sexually, by internal fertilization
Most live in moist soil/decomposing organic matter, play large role in decomposing and nutrient cycling
Sometimes they attack the roots of plants, some are parasites
o Pinworms and hookworms: acquire nematode by eating raw/undercooked pork that has juvenile
worms encysted in muscle tissue
o Have really badass molecular toolkits that allows them to redirect some for the cellular functions
of their hosts
ARTHROPODS
ORIGINS
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Segmented bodies, hard exoskeleton and jointed appendages
Have two unusual hox genes, both of which influence segmentation
GEN CHARACTERISTICS
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Appendages of some arthropods have been modified, specializing in functions such as
walking/feeding/reproduction/etc
Body is completely covered by a cuticle, exoskeleton constructed from layers of protein
o Some parts are thick and hard and others are thin and flexible
o Cannot grow without shedding its exoskeleton, producing a larger one—molting is energetically
expensive, vulnerable to predation until its new exoskeleton hardens
o Initial functions were protection and anchorage for muscles,  enabled evolution onto land
o Impermeability to water helped prevent desiccation, strength solved problem of support
Have well-developed sensory organs—eyes, olfactory receptors and antennae
Open circulatory system: fluid called hemolymph is propelled by a heart through short arteries and then
into spaces called sinuses surrounding the tissues/organs
o Reenters the heart through pores that equipped w/ valves
o Hemocoel: hemolymph-filled body sinuses, not part of the coelom
Gas-exchanged organs
o Allow diffusion of respiratory gases in spite of exoskeleton, most have gills w/ extensions that
place extensive SA in contact w/ surrounding water
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The subphylum include: cheliceriforms, myriapods, hexapods and crustaceans
CHELICERIFORMS
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Sea spiders, horseshoe craps, scorpions, ticks, mites spiders
Named for claw-like feeding appendages called chelicerae, which serve as pincers or fangs
Have anterior cephalothorax and a posterior abdomen
Lack antennae and have most simple eyes
Eurypterids: earlies forms, water scropions
Arachnids: group includes scorpions, spiders, ticks and mites
o Have a cephalothorax that has 6 pairs of appendages: chelicerae, pedipalps (sensing, feeding,
reproduction)
o Use their fangs like chelicerae, which are equipped with poison glands
Book lungs: gas exchange, stacked platelike structures contained in an internal chamber
Spiders can spin webs of silk, inhered behavior
MYRIAPODS
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Millipedes and centipedes
All are terrestrial
Mandibles: modified mouth parts, jaw-like
Millipedes (Diplopoda) have a larger number of legs
o Each trunk segments is formed from two fused segments and bears two legs
o Eat decaying plant matter
Centipedes (Chilopoda) are carnivores
o Each segments of the centipede’s trunk region has one pair of legs
o Have pison claws on their foremost trunk segment that paralyzes prey
INSECTS
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More species rich than all of the other forms of life combined
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Live in almost every terrestrial habitat and in fresh water
Flight
o One of the great success of insects – escape predators, find food and mates, disperse to new
habitats faster
o Have one/two pairs of wings that merge from dorsal side of the thorax, extensions of the cuticle
and not true appendages—can fly wi/o sacrificing any walking legs
o May have first evolved to absorb heat, allowed them to glide from vegetation to ground/served
as gills
o Wings evolved only once in insects
 Dragonflies were the first to fly, other insect orders evolved later than dragon flies
Incomplete metamorphosis: grasshoppers—young resemble adults but are smaller, have different body
proportions and lack wings – NYMPH undergoes series of molts, each time looking more like an adult
Complete metamorphosis: larval stages specialized for eating/growing – caterpillar/maggot/grub—looks
entirely different from the adult stage
Reproduction is usually sexual, with separate male/females – fertilization is usually internal
o Insects can only mate once in a lifetime
Numerous, diverse, widespread, etc
o We depend on them for a lot. Yknow. Food and all.
CRUSTACEANS
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Remain in marine/freshwater environments
Highly specialized appendages
o Antennae, mouthparts, walking legs, abdomen appendages
o A lost appendage can be regenerated at the next molt
Small crustaceans exchange gases across thin areas of cuticle, larger ones hav egills
Sexes are separate inmost
Isopods: include terrestrial, freshwater and marine species; abundant in habitatas at the bottom of the
ocean
Decapods: lobsters, crayfishes, crabs, shrimp; cuticle is hardened by calcium carbonate, marine
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Copepods: marine/freshwater plankton community members, krill
Barnacles: mostly sessile crustaceans whose cuticle is hardened into a shel, anchor themselves to surfaces
and extend appendages to food to eat
33.5: ECHINODERMS AND CHORDATES ARE DEUTEROSTOMES
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They all have a backbone, clade of bilaterian animals – defined by DNA similarities, not developmental
similarities
ECHINODERMS
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Echinoderms: spiny skin—slow-moving, sessile marine animals
o Thin epidermis covers endoskeleton of hard calcareous plates
o Prickly from skeletal bumps/spines
Water vascular system: network of hydraulic canals branching into extensions called…
Tube feet: that function in locomotion, feeding and gas exhcnage
Sex: involves separate male/female, external fertilization
Internal/external parts radiate from center—symmetry is not truly radial
SEA STARS
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Have multiple arms radiating from central disk, undersurfaces of which bear tube feet
o Use feet to move- creep slowly
o Attach to their prey
 Arms embrace the closed bivalve
 Sea star turns part of its stomach inside out, everting it through its moth
 Digestive system starts softening the prey
Powers of regeneration
o Can grow lost arms, some can grow an entire body from a single arm
BRITTLE STARS
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Lacks the flattened disk found in sea stars, but does screte adhesive chemicals, use tube feet to grip
substrates
Some are suspension feeders, other are predators
SEA URCHINS
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Have no arms, have rows of tube feet that function in slow movement
Mouth is ringed by highly complex, jaw-like structures that are adapted to eating seaweed
SEA LILIES AND FEATHER STARS
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Lilies attached to substrate by stalk, feather stars crawl about using their long, flexible arms
Suspension feeding
SEA CUCUMBERS
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Lack spines, endoskeleton is reduced
Elongated in oral-aboral axis, giving them their shape
Have five rows of tube feet, some around the mouth developed as feeding tentacles
SEA DAISIES
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Body is armless and typically disk-shaped
Five-sided organization and measure less than a cent in diameter
Edge is ringed with small spines
Absorb nutrients through the membrane
CHORDATES
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Bilaterally symmetrical coelomates w/ segmented bodies
34.1: CHORDATES HAVE A NOTOCHORD AND A DORSAL , HOLLOW NERVE CHORD
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Chordates: bilaterian (bilaterally symmetrical) animals, belong to the Deuterostomia
DERIVED CHARACTERS OF CHORDATES
NOTOCHORD
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Notochord: longitudinal, flexible rod located between the digestive tube and the nerve cord
o Composed of large, fluid-filled cells encased in stiff, fibrous tissue
o Provides skeletal support throughout most of the length of a chordate
DORSAL, HOLLOW NERVE CORD
 The nerve cord of a chordate embryo develops from a
plate of ectoderm that rolls into a tube located dorsal to the
notochord
 Resulting tube is a nerve tube unique to chordates
 Nerve tube develops into the central nervous system
(brian/spinal cord)
PHARYNGEAL SLITS OR CLEFTS
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Pharyngeal clefts: grooves that form along the sides of the pharynx, develop into slits that open to the
outside of the body
Pharyngeal slits: allow water entering the mouth to exit the body w/o passing through the entire
digestive tract.
o Function as suspension-feeding devices In many invertebrate chordates
o Have been modified for gas exchange and are known as gill slits
MUSCULAR, POST-ANAL TAIL
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Have a small tail that extends posterior to the anus, reduced during embryonic development
LANCELETS ^
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Lancelets: get their name from their bladelike shape
Develop notochord, dorsal-hollow-nerve-cord and numerous pharyngeal slits and post-anal tail
Larvae feed on plankton in water column, alternating between upward swimming/passive sinking
Adults can reach 5 cm, retain key chordate trains
o Adult lancelet swims down to the seafloor and wriggles back into the sand, leaving only its
anterior end exposed
o Cilia draw seawater into the lancelet’s mouth, net of mucus removes tiny food particles from the
water
o Somites: blocks of the mesoderm muscle segments develop from
TUNICATES
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Tunicates: more closely related to other chordates than are lancelets
o Characteristics are most apparent during their larval stage
o Uses its tail and muscles and notochord to swim through the water
o Once a tunicate has settled on a substrate, it undergoes a metamorphosis in which many of its
chordate characters disappear
 Tail and notochord are resorbed, nervous system degenerates, remaining organs rotate
 Incurrent siphon
 Foot particles are filtered from water by mucous net
 Anus empties into the excurrent siphon
 Degenerate adult stage only evolves only after tunicate lineage branched off from other
chordates
 Tunicate larva appears to be highly derived
 Hox genes difference
EARLY CHORDATE EVOLUTION
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Lancelets have a number of chordate characters as adults and their lineage branches from the base of the
chordate phylogenetic tree
o Ancestral chordate = lancelet: anterior end w/ mouth, notochord, dorsal-hollow nerved cord,
pharyngeal slits and post-anal tail
Why do we have to know this? Fuck it.
34.3: VERTEBRATES ARE CRANIATES THAT HAVE A BACKBONE
DERIVED CHARACTERS OF VERTEBRATES
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Dlx family: resulting genetic complexity
o Innovationsin the vertebrate nervous system and skeleton
o Extensive skull and backbone composed of a vertebrae
LAMPREYS
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Oldest living lineage of vertebrates
OH MY GOD NOT FUN EW EW EW EW EW EW EW EW EW EW EW EW EW
Larvae live in freshwater streams
o Most lampreys migrate to the sea and mature AND SUCK YOUR FACE OFF AHHHHHHHHHHHH
Skeleton made out of cartilage
o Made of stiff protein matrix
o Notochord persists as the main axial skeleton
FOSSILS OF EARLY VERTEBRATES
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Conodonts: slender, soft-bodied vertebrates with prominent eyes controlled by numerous muscles
o Had hooks in their mouths
ORIGINS OF BONE AND TEETH
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Mineralization  feeding mechanisms
o Chordates (suspension feeders)  digesting small animals
Skull?
34.4: GNATHOSTOMES ARE VERTEBRATES THAT HAVE JAWS
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Gnathostomes: jawed vertebrates
DERIVED CHARACTERS OF GNATHOSTOMES
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Named for their hinged jaws with teeth that enable the gnathostomes to grip food items firmly and slice
them
Anterior gill slit—respiratory gas exchange
Additional duplication of hox genes  1 became four
o Forebrain is enlarged and has enhanced sense of smell and vision
Lateral line system: organs which form a row along each side of the body, sensitive to vibrations in the
surrounding water
FOSSIL GNATHOSTOMES
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Paired fins and tail allowed them to swim efficiently
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Jaws enabled them to bite off chunks of flesh
Placoderms: earliest gnathostomes, “plate-skinned” – less than a meter long
Acanthodians: jawed vertebrates that disappeared later
CHONDRICHTHYANS (SHARKS, RAYS, COMPANY)
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Chondrichthyan: cartilage fish
o Streamlined body, swift swimmers, but can’t maneuver very well
o Movements of the trunk and caudal fin propel them forward
o Dorsal fins are just stabilizers – more dense than water and if it stops swimming, it sinks
o Sharks don’t have lungs – gas exchange in the mouth and out of gills
o Largest sharks and rays are suspension feeders that consume plankton
o Most sharks are carnivores
 Sharks have large rows of teeth that rotate
 Digestive tract is smaller
 Intestine is a spiral valve, which increases surface area and prolongs the passage of food
through the digestive tract
o Sharks have sharp vision but can’t distinguish colors
o Have really awesome nostrils for smelling
o Regions of skin that can detect electric fields generated by muscle contractions of nearby animals
o No eardrum
o Eggs are fertilized internally
 Oviparous: lay eggs that hatch outside the mother’s body
 Claspers: male uses these to transfer sperm
 Ovoviviparous: retain fertilized eggs in the oviduct—develop into young that are born
after hatching within the uterus
 Viviparous: young develop in the uterus and obtain nourishment prior to birth by
receving nutrients via placenta
 Cloaca: common chamber that has a single opening to the outside
o Rays vs Sharks
 Rays are bottom dwellers
 Use their flattened shape to propel themselves through the water
 Tail of many rays is whiplike and have barbs
RAY-FINNED FISHES AND LOBE-FINS
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Clade: Osteichthyes
o Bony fish – body endoskeleton with a hard matrix of calcium phosphate
o Operculum: protective bony flap which covers the gills
o Swim bladder: air sac that controls buoyancy of a fish
o Skin of a fish is covered by flattened, bony scares that differ in structure, secrete slimy mucus to
reduce drag while swimming
RAY -FINNED FISHES
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Ray-finned fishes: fins are supported by bony rays and are modified for maneuvering, defense, etc
o Originated in fresh water and spread to seas
o Serve as a major source of protein for humans, who have harvested them for years
LOBE-FINS
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Lobe-fins: presence of rod-shaped bones surrounded by a thick layer of muscle in their pectoral and pelvic
fins
o Lived in brackish water, used their lobed fins to swim and walk underwater across the substrate
o Coelacanths (SE Asia), Lungfishes and tetrapod
34.5: TETRAPODS ARE GNATHOSTOMES THAT HAVE LIMBS
DERIVED CHARACTERS OF TETRAPODS
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Tetrapods: four feet – limbs that can support their weight on land and feet w/ digits that allow them to
transmit muscle-generated forces to the ground whenthey walk
o Head is separated from the body by a neck
ORIGINS OF TETRAPODS
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Fins became more progressively limb-like  amphibians
AMPHIBIANS
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Amphibians: represented by salamanders, frogs, caecilians
Urodela: salamanders: live on land as adults – side to side bending of the body
Anurans: frogs: powerful hind legs, great adaptations like poisonous skin glands and camouflage
Apodans: legless and nearly blind, resemble earthworms
Amphibians can live on both water and land (tadpole – froggy)
o Most are found in damp habitats bc of lung adaptations—reliance on moisture for gas exchange
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Fertilization is external in most cases – awkward restrained frog sex
o Typically lay their eggs in the water, dehydrate quickly b/c they lack a shell
o Social behaviors? – males vocalize to defend breeding territory/attract females
34.6: AMNIOES ARE TETRAPODS THAT HAVE A TERRESTRIALLY ADAPTED EGG
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Amniotes: group of tetrapods whose extant members are reptiles and mammals
DERIVED CHARACTERS OF AMNIOTES
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Amniotic egg: four specialized membranes: amnion, chorion, yolk sac and allantois
o Reptiles have a shell—made of calcium
o Slowls down dehydration in the air
Use their rib cage to ventilate their lungs – rib cage ventilation, abandon breathing through skin and
develop less permeable skin (conserving water)
EARLY AMNIOTES
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They could live in drier environments than did he first tetrapods
REPTILES
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Reptile : clade includes tuataras, lizards, snakes, turtles, crocodilians and birds
Have scales that contain keratin – help protect skin from dessication and abrasion
Most reptiles lay shells eggs on land – internal fertilization
“cold blooded” do not use metabolism to control their body temperature, instead have behavioral
adaptations
o Ectothermic: absorb external head as their main source of body heat
o Vs endothermic: regulate body temp through metabolic activity
ORIGIN AND EVOLUTIONARY RADIATION OF REPTILES
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Parareptiles: first major groups of reptiles to emerge—large, stocky quadrupedal herbivores – died out by
the end of the Triassic period
Diapsid: pair of holes on each side of the skull, behind the eye socket
o Lepidosaurs: tuataras, lizards and snakes
o Archosaurs: crocodilians
o Pterosaurs: first tetrapods to exhibit flapping flight
o Dinosaurs: very diverse little critters
 Theropods: bipedal carivores – T-rex
Dinosaurs gave rise to birds – endothermic – metabolism debate?
They were really fast and badass.
And they all became extinct. How upsetting.
LEPIDOSAURS
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Tuataras: feed on insects, small lizards and bird eggs and chicks
o Lizards and snakes – squamates – most numerous and diverse reptiles alive today
o Snakes are legless lepidosaurs whose closest living relatives include the Komodo Dragon
o Snakes are proficient at moving on land, producing waves of lateral bending that pass from head
to tail
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o
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Carnivorous—acute chemical sensors, lack eardrums but sensitive to ground vibrations
Heat-detecting organs between eyes and nostrils help them locate the prey
Flicking tongue fans odors towards olfactory organs
Poison through the hollow teeth
Loose jawbones and elastic skin enable most snakes to swallow huge prey
TURTLES
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Box-like sell made of upper and lower shields fused to the vertebrae, calvicles and ribs
Not closely related to archosaurs
Earliest turtles could retract their head into shell
Adapted to deserts, seas, ponds, rivers
ALLIGATORS AND CROCODILES
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Quadrupeds w/ long, slender legs – larger and adapted to aquatic habitats w/ nostrils that turned
upwards
BIRDS
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Birds are archosaurs – almost every feature has been modified to flight
DERIVED CHARACTERS OF BIRDS
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Lack urinary bladder, females only have one ovary
o Gonads are small except during breeding season
o Toothless, trims weight of the head
Wings and feathers – feathers made of B-keratin
o Flight + = enhances hunting and scavenging, eat bugs, ready escape from predators, migrate
distances to exploit different food resources and seasonal breeding areas
Great amounts of energy
o Endothermic – constant high body temp
o Efficient resp system and circ system
Acute vision and fine muscle control
Complex breeding behaviors
THE ORIGIN OF BIRDS
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From dinosaurs? That decided they needed to not be captured by predators?
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Ratites: ostrich, rhea, kiwi, cassowary, emu: all flightless
34.7: MAMMALS ARE AMNIOTES THAT HAVE HAIR AND PRODUCE MILK
DERIVED CHARACTERS OF MAMMALS
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Mammary glands: produce milk for their offspring
o Milk is balanced w/ fats and sugars and proteins and minerals and vitamins
Hair: retain heat
Endothermic, high metabolism—efficient resp and circ systems
Long duration of parental care
Larger brain
Differentiated teeth
EARLY EVOLUTION OF MAMMALS
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Synapsids: lacked hair, had sprawling gait and laid eggs—single temporal fenestra (hole behind eye socket
on each side of the skull.)
 large herbivores and carnivores  three major lineages
o Monotremes
o Marsupials
o Eutherians
MONOTREMES
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Monotremes: found only in Australia and New Guinea—echidnas and platypus
o lay eggs, but have hair and produce milk, but lack nipples
MARSUPIALS
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Marsupials: higher metabolic rates and nipples, give live birth
o Embryo develops inside a uterus, lining of the uterus form the placenta
o Marsupial is born early and completes its embryonic development while nursing in a pouch
EUTHERIANS (PLACENTAL MAMMALS)
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Eutherians: their placentas are more complex than those of marsupials and have longer pregnancies
PRIMATES:
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Opposable thumbs and forward facing eyes