Ch. 24

Question 1

Animals: Cell Structure and Specialization

Answer 1

• Animals are multicellular eukaryotes
• They lack cell walls (unlike plants and fungi)
• Their bodies are held together by an extracellular matrix (ECM) - structural proteins such as collagen
• Nervous tissue and muscle tissue are unique, defining characteristics of animals →ability to move!
• Tissues are groups of cells that have a common structure, function, or both: true tissues separated by membranous layers

Question 2

Characteristics of Animals

Answer 2

• Chemoheterotrophic: cannot make own carbon-based food source, must consume other organisms
• Sexual reproduction (mostly): motile haploid sperm fertilizes larger non-motile haploid egg to make diploid zygote
• Capable of movement: at least one stage of life cycle

Animal Diversity:
• Basal Phyla
• Protostomes
• Deuterostomes

Question 3

Motility (movement) in Animals

Answer 3

• Some are only able to move around for part of their lives
• Some are sessile (stationary/not moving) for a portion of their life cycle
(e.g., during adulthood)

Question 4

Key innovations in animal evolution

Answer 4

1. Patterns of embryonic development
2. Development of different tissues
3. Type of body symmetry
4. Presence or absence of a body cavity

Question 5

Homeotic Genes in Animals

Answer 5

• Highly conserved nucleotide sequence
• Present in all eukaryotes with crucial role in
development of morphogenesis
• Regulatory genes (that produce proteins)
→turn other genes on and off
(subset of homeotic genes found in animals)
• Control anterior to posterior developmental sequence of embryo (i.e., pattern of formation during development)
✓order of Hox genes along chromosomes is similar among different groups of animals (homologous)
✓but number of repetitions can differ

• Number of Hox genes varies among animal phyla
─absent in sponges, few in jellyfish, more in arthropods and many in vertebrates (and chordates)
• Result of several gene duplication events over evolutionary time

Question 6

Reproduction and Embryonic Development

Answer 6

• Most animals share similar pattern of early embryonic development:
• Have haploid gametes of different sizes - small motile sperm,
- large non-motile eggs
• Diploid zygote undergoes a number of mitotic cell divisions = cleavage

• Cleavage leads to formation of a multicellular, hollow blastula
• The blastula undergoes gastrulation, forming a gastrula with different layers of embryonic tissues
• During development, germ layers give rise to the tissues and organs of the animal embryo

Question 7

Embryonic Development

Answer 7

Protostomia: first invagination of the gastrula (blastopore) becomes the mouth
• proto = first, stoma = mouth

Deuterostomia: second invagination becomes the mouth
- deutero = second
(first opening become anus, or closes up)

Protostomes vs. Deuterostomes

Protostomes:
(A) Cleavage: 4-cell embryo —> 8-cell embryo, spiral cleavage
(B) mesoderm and coelom formation: it just looks different, may have to draw it out somewhere
(C) origin of mouth and anus: blasotpore develops into mouth; anus forms later

Deuterostomes:
(A) Cleavage: 4-cell embryo —> 8-cell embryo, radial cleavage
(B) mesoderm and coelom formation:
(C) origin of mouth and anus: blastopore develops into anus; mouth forms later

Question 8

Cell Cleavage

Answer 8

• Protostomes: the new row of cells is twisted slightly off centre:
— spiral cleavage
— determinate: new cell is destined to form some part of the later embryo (removal of some cells results in embryo missing organs)

• Deuterostomes: each cell division stacks the new cells directly above the previous ones
— radial cleavage
— indeterminate: early embryonic cells not differentiated (could split young embryo and get two complete later embryos→identical twins!)

Question 9

Animal Development

Answer 9

• Direct development: embryo continues gradually on towards adult form
• e.g., humans
• Indirect development: intervening stages (larvae) whose morphology and behaviour differs greatly from sexually mature adult stage
• e.g., caterpillar→butterfly

Question 10

Eumetazoa

Answer 10

• Animals with true tissues
• Tissue = integrated group of cells with common structure and function, isolated from other tissues by membranous layers Protostomia

• Parazoan design: aggregate of cells; specialized cells for different functions

• Eumetazoan design: specialized cells aggregated into distinct tissues; more advanced designs, tissues combine → organs

Question 11

Origin of Embryonic Tissue Layers and Muscles

Answer 11

• While sponges have the genetic tool kit needed for cell-to- cell and cell-to-extracellular matrix (ECM) adhesion:
─ they do not form complex tissues
• Animals other than sponges are divided into two groups: ─ based on the number of embryonic tissue layers they have
─ And they do not form complex tissues

Question 12

Germ layers

Germ Layers→Tissue

Answer 12

• Diploblastic → 2 germ layers
• Triploblastic → 3 layers

Diploblastic .vs. Triploblastic
• Germ layers:
— endo-→digestive tract (gut)
— ecto -→outer covering (skin & nerves)
— meso-→muscle and other organs

• “Radiata”: 2 embryonic cell layers
— diploblastic: endo- and ectoderm

• Bilateria: 3 embryonic cell layers
— triploblastic: endo-, ecto- and mesoderm (meso = middle)

Question 13

Body plans: symmetry

Answer 13

• Asymmetric: lacking symmetry
– e.g., sponges

• Radial symmetry: no front and back, or left and right
– e.g., sea anemones, comb jellies

• Bilateral symmetry: two-sided symmetry
– e.g., lobster, humans

(a) Radial symmetry
— Radial animals are often sessile or planktonic (drifting or weakly swimming)

(b) Bilateral symmetry
— Bilateral animals often move actively and have a central nervous system

Bilaterally symmetrical animals have
– A right and left side
– A dorsal (top) side and a ventral (bottom) side
- Anterior (head) and posterior (tail) ends
- Note: Cephalization, the development of a head (central nervous system)

Question 14

Body Symmetry

Answer 14

• asymmetric
# planes of symmetry: 0
locomotory abilities: sessile (no movement)
degree of cephalization: no head
Lifestyle: suspension feeders

• bilaterally symmetric
# planes of symmetry: 1
locomotory abilities: Highly mobile with lots of variation (some exceptions)
degree of cephalization: highly cephalized (some exceptions)
Lifestyle: Seek food (exceptions)

• radially symmetric
# planes of symmetry: >1
locomotory abilities: Usually poor
degree of cephalization: weak to none
Lifestyle: variable but often trap prey

Question 15

Associations between Body Symmetry and Nervous System

Answer 15

Radial symmetry = Nerve network

Bilateral symmetry = Central Nervous system

Question 16

Bilateral Symmetry and Cephalization

Answer 16

• Concentration of sensory organs in head
— e.g., sensory structures, receptors
— internal concentration of neural system → brain!

• Adapted for forward & direction movement
— quicker response to stimuli in environment
— better able to search for food
— better defenses capabilities

The Tube-within-a-Tube Body Plan
is common in triploblastic animals (especially in bilaterally symmetrical animals)
Animals May or May Not Have a Body Cavity

Question 17

Body Cavities

Answer 17

• Most triploblastic animals possess a fluid-filled body cavity
• A true body cavity is called a coelom, derived from mesoderm
• Coelomates are animals that possess a true coelom

(A) Coelomate:
•Coelom
•Body covering (from ectoderm)
•Tissue layer lining coelom and suspending internal organs (from mesoderm)
•Digestive tract (from endoderm)
— Earthworms Arthropods Mollusks Echinoderms Vertebrates Etc…

• Pseudocoelomate: animals that lack complete mesodermal lining
• Triploblastic animals that possess a pseudocoelom are called:

(B) Pseudocoelomate
• Pseudocoelom
• Body covering (from ectoderm)
• Muscle layer (from mesoderm)
• Digestive tract (from endoderm)
• Phylum Nematoda

• Triploblastic animals that lack a body cavity are called acoelomates

(C) Acoelomate
• Body covering (from ectoderm)
• Tissue- filled region (from mesoderm)
• Wall of digestive cavity (from endoderm)
• Phylum Platyhelminthes

Question 18

Function of body cavity?

Answer 18

• Fluid-filled cavity can be used as hydrostatic skeleton and help with movement
— by tensing muscles around incompressible fluid
• Cushions internal organs from blows to outside body (protection)
• Allows functioning of some internal organs
— e.g., digestive organs may only be able to function properly if they are
free to move, such as through muscle movements for moving food through the digestive tract
• Allows internal organs to shift without deforming outside of
body
— e.g., movement of guts, beating of heart
• Note: coeloms independently gained and lost (evolutionarily) in different animal lineages.

Question 19

Evolutionary Relationships Among the Animals

Key shared derived characters

Answer 19

• Common ancestor resembled Choanoflagellates
• heterotrophic protist
• single flagellum surrounded by collar of microvilli (finger-like projections of cell membrane)
• cell morphology very similar to that of sponges (Porifera)

Question 20

Three lines of evidence that choanoflagellates are closely related to animals

Answer 20

1. Cell morphology similar in
   choanoflagellates and sponges
2. Cell morphology unique to animal cells
3. DNA sequence homology

Question 21

Evolution of Multicellularity

What’s the advantage of multicellularity?

Answer 21

Hypothesis: ball-shaped colony of choanoflagellates may have evolved into a simple animal with endo- and ectodermal layers.

• If cooperative aggregations of cells are able to survive better and produce more offspring than their unicellular counterparts (higher relative fitness), then these various evolutionary pathways could all be possible.
— What is the role of Natural Selection in this progression?

What’s the advantage of multicellularity?
• cooperation and coordination among cells
• = cells can specialize for different functions (= different cells)
✓protective skin
✓enzyme secretion for trapping food ✓coordinated movement
✓specialized cells for reproduction

Question 22

Diversity of Kingdom Animalia

Answer 22

Invertebrates are a Paraphyletic Group

Basal phyla Includes:
• Asymmetric body plans
• Radialsymmetrybody plans

Bilateria Includes:
• Mostly Bilateral
symmetry body plans
• Exceptechinoderms
with mostly radial symmetry

Question 23

The Sponges: Phylum Porifera

Phylum Porifera

Phylum Porifera: characteristics

Lifestyle

Answer 23

• por = pore + fer = to bear
• Lack hox genes and no symmetry
• ~ 8000 extant species, 99% are marine
• Range from a few mm to a few m in
height
• Except for larval stage, they are mostly
sessile
─ attached to one spot, do not move

Phylum Porifera: characteristics
• No obvious tissues or organs
─e.g., no gut, no muscles, no nervous system
• Structural support comes from spicules ─tiny, hard needles or rods
─calcium carbonate or silica
• Some sponges have only tough collagen-protein network for support (= spongin)
• 2 major cell types
─ choanocytes – flagellated for creating stream of water for
feeding
─ amoebocytes – motile, moves nutrients between cells

Lifestyle
• They are suspension feeders → filter food out of the water
─ use cells called choanocytes that have flagella and draw water into the sponge through pores called porocytes

Question 24

Eumetazoans

Answer 24

• specialized cells aggregated into distinct tissues; more advanced body plans, tissues combine → organs

Question 25

Phylum Ctenophora

Answer 25

• Gelatinous body
• Have combs – fused cilia arranged
in plates, used in locomotion
• More complex than some other groups of animals (e.g., sponges)
─ have a nervous system

Question 26

Phylum Cnidaria

Answer 26

• Includes jellyfish, hydras, sea anemones, corals
• ~10,000 extant species (99.9% marine)
• Eumetazoans: have true, differentiated tissues
• Diploblastic = two layers (ecto- and endoderm)
• Most have radial symmetry & simple body plan
• Cnidarians are named for unique cells = cnidocytes
─ A specialized cell used for feeding & defense
• Each cnidocyte contains very complex endocellular structure
- most common type is nematocyst
• Have a sac-like body, with a mouth surrounded by tentacles
• Have nerve cells
• Cnidocytes can send out a barbed nematocyst that can puncture and capture prey (feeding)
• Reproduction: many species alternate between the medusa and polyp forms
─ Often one form (medusa or polyp) is dominant
─ Produce planula (larvae) through sexual reproduction

Two basic body forms:

• Polyp (sessile form): oral end upwards, attached to a substrate

• Medusa (motile form): oral end downwards, moves freely through the water via hydrostatic skeleton

Question 27

Life cycles in cnidarians

Answer 27

• Have asexual or sexual reproduction
• Haploid gametes (sperm and eggs) are
produced during sexual reproduction
• Some are polymorphic (like most “invertebrates”)
─ Have more than one form during their life cycle
→ Benefit: can exploit different types of environments during different life stages

Question 28

Corals – specialized mutualism

Answer 28

Anthozoa – coral polyp
zooxanthellae
= dinoflagellates

Question 29

KEY CONCEPTS

Answer 29

• Animals are a monophyletic group, with sponges as the basal animal
• The evolution of animals is more complicated than a smooth transition from simple to complex
─ Many key innovations did not arise all at once
─ Evolution did not stop within any of the lineages
• Body symmetry is a key morphological aspect of an animal’s body plan

Question 30

…

Answer 30

Diploblastic:
Ancestral colonial flagellate —> Metazoa —> Eumetazoa —> Cnidaria + Ctenophora

Triploblastic:
Ancestral colonial flagellate —> Metazoa —> Eumetazoa —> Bilateria —> deuterostomia + protostomia

Deuterostomia —> ectoprocta + brachiopoda + (echinodermata + chordata)

protostomia —> platyhelminthes
protostomia —> rotifera + mollusca (Annelida + arthropoda) + nematoda

Question 31

Kingdom Animalia: Protostomes

Answer 31

• monophyletic

•Lophotrochozoa
— platyhelminthes, rotifera, ectoprotca, brachiopoda, annlide

• ecdysozoa
— Nematoda, Arthropoda

• Protostome embryos typically have determinate, spiral cleavage as cells divide
• Protostome mesoderm differentiates near the blastopore and forms a coelom (schizocolom) within the mesoderm.
• In Protostomes the blastopore becomes the mouth and a second, later opening becomes the anus.

Question 32

Clade Bilateria

Answer 32

• Bilateral symmetry
• Varying degrees of cephalization (differentiation of a head region)
• anterior concentration of neural ganglia (brain)
• reduced in sedentary animals (e.g., clams) • Triploblastic
• endo-,ecto-andmesoderm

• Nephrozoa refers to the presence of an excretory system

Question 33

Protostomes are Monophyletic with two major lineages

Answer 33

• Fossils indicate both lineages originated in the ocean:

– Protostomes made the transition from water to land multiple times as they diversified

– Challenges:
1. Avoid drying out
2. Gas exchange
3. Hold up bodies

Question 34

Lophotrochozoans and Ecdysozoans differ in their mechanism of growth

Answer 34

Lophotrochozoans: Incremental growth

Ecdysozoans: Moult between growth phases

Question 35

Superphylum Lophotrochozoa

Answer 35

• includes ~18 phyla

• range from morphologically very simple (e.g., flatworms) to morphologically and behaviourally very complex (e.g., mollusks like octopuses)

• some have lophophore larval stage and others have trochophore larvae

• Relationships among lophotrochozoan phyla unclear
– Lophotrochozoa identified by molecular data

Clade Lophotrochozoa
Clade is polyphyletic!!
Very different animal types What do they share?
Protostome development
• first invagination = mouth • spiral cleavage
Unique molecular characters

Question 36

Phylum Platyhelminthes

Answer 36

• Flatworms (~20, 000 species) • platy = flat, helminth = worm

• Acoelomate

• triploblastic

• but no fluid-filled body cavity

• basically solid tissue

• Most have eye spots (called ocelli)

• No special circulatory or gas-exchange system – How do they “breathe”?

• Nervous system has few ganglia (cluster of nerve cells)

• Do not have a complete digestive system
✓ have a mouth and a gut lumen, but no anus
✓ so, their excretory tube lacks an internal opening
✓ some parasitic ones lack mouths and guts
Consequences of body plan?

• bilateral symmetry → cephalization
• flattened body → larger surface area → nutrients and gases diffuse more efficiently (in water)

Question 37

Phylum Annelida (~16,500 spp.)

Answer 37

• Segmented worms (annulus = ring)

• polychaetes, earthworm-like worms, leeches

characteristics
• Segmented
─ many repeated units with similar internal and external anatomy (divided by septa)
• Eucoelomate
─ body cavity completely lined with mesodermally derived tissues
─ hydrostatic skeleton
• Closed circulatory system
• blood contained in vessels
• Gas exchange via skin
• Complete digestive system with anus
• applies to all subsequent taxa
• Excretory system
• Nervous system

Question 38

Phylum Mollusca

Answer 38

• The basic body plan is highly adaptive
• 2nd only to Arthropods
• ~93,000 named species
─ snails, clams, squids and many others
• 8 classes
• Most marine, but many freshwater and terrestrial
• Calcareous (i.e., calcium carbonate) shell enclosing soft body
• Shell lost or reduced in many taxa
─ moll = soft, originally named for octopuses and
cuttlefish

characteristics
• Mantle: thin layer of tissue that secretes shell • Muscular ventral foot used for movement
• Organs contained in a visceral mass above foot
• Mouthparts a straplike rasping organ called radula

• Gills for gas exchange and sometimes for feeding
─ e.g., bivalves like scallops
• Open circulatory system (most) ─ blood not in vessels
─ coelom reduced
• Not clearly segmented
• Many with trochophore larvae
• e.g., snails, nudibranchs, clams, mussels, squid, octopus
• very diverse phylum, with the following similarities…
— Visceral mass (internal organs)
— Mantle (tissue that may secrete shell)
— Foot (muscular, often aids in movement)
→these 3 structures are highly modified in each group of mollusks depending on their lifestyle!

Question 39

Superphylum Ecdysozoa

Answer 39

(ecdysis = molting)
• Ecdysozoans are the most species-rich animal group
• 8 phyla
• Ecdysis: process of molting the cuticle in order to grow
– entire cuticle shed at once
– cuticle = non-living outer layer of skin
• Cuticlefrequentlysclerotized
– scler = hard
• Only particular regions are hardened
– called sclerites when shaped like plates
• Unsclerotizedcuticleinbetween
– flexible, allows for movement

About the cuticle
• Below cuticle is epidermis: living cells that secrete substances→cuticle
• Cuticle has 3 layers:
– endocuticle (endo = within) – exocuticle (exo = outside)
– epicuticle (epi = upon)
• very fine ducts run from epidermis to top of cuticle

Question 40

Phylum Nematoda

Answer 40

• Roundworms, threadworms – nemato = thread
• 0.3 mm – 8+ meters long (most < 5mm)
• ~25,000 named species
– estimates of up to 100 x more
• Morphologically similar* – no segmentation
– no appendages
– no eyes
– slightly blunt at one end, slightly pointy at the other
• Must shed cuticle too - moult like other Ecdysozoa

*Note: Simplicity in this case is an example of “secondary” simplification derived from a more complex body plan.

• Pseudocoelomate
– body cavity, not completely lined by mesoderm
• Two sexes:
– internal fertilization
– some are hermaphrodites
• Provide an example of how the pseudocoelom can
help in movement:
1. longitudinal muscles occur along its length
2. to move, they contract the muscles
3. the pressure (called hydrostatic pressure) in the
pseudocoelom straightens the animal once the muscles relax
→ Move side-to-side by contraction of longitudinal body wall muscles

Question 41

Phylum Nematoda vs. Phylum Annelida

Answer 41

• pseudocoelomate
— cavity between meso & endo

• coelomate
— cavity lined with mesoderm

Question 42

Phylum Arthropoda

Answer 42

Origins of diversity?
• Morphological and physiological diversification has a genetic basis
•Until recently, biologists wrongly assumed that very different organisms required very different genetic instructions

• Earliest confirmed fossils:Cambrian explosion(~500Mya)
• Most species-rich phylum of any organism (~1 million living, named
species; estimated more than 3 millions!)
– estimates of 3-30 million in total
– 3 out of every 4 named species of animals is an arthropod
• Mostecologically important group of animals – especially decomposition and pollination

Characteristics
• Cephalization
– nervous tissue becomes concentrated toward head during
course of evolution
– head region composed of several segments specialized for feeding and sensing
• Open circulatory system
– hemolymph in hemocoel
• Jointed appendages
– arthros = joint, pod = foot
– specialized functions (walking, feeding, sensory, reproduction, defense)
• Segmented body
– Changes to regulation of Hox genes
• Sclerotized cuticle made of chitin – acts as an exoskeleton
– must moult to grow
– provides support (life on land!) and a rigid surface for muscle attachment

Question 43

Morphological diversity

Answer 43

• Multicellular animals have a common tool kit of genes that establish the animal body plan during development (recall: Hox genes)
– Expressing the genes in the tool kit at different times and different places during development can lead to dramatic differences
• Variation in Gene expression + Ecological opportunity = Diversity

• Diversification of animal body plans can occur by the generation of new genes over time
• However, changing the expression pattern of existing genes likely had an even larger impact on animal body plan diversification
– a small set of elements can be reused and rearranged to produce a large variety of outcomes

Question 44

What traits should Arthropods share?

Answer 44

Clade Metazoa
1. Collagen, multicellular, motile
2. Tissues, gastrulation, hox genes, symmetry
3. Bilateral, triploblastic, cephalization, coelom?
4. Protostome (spiral, determinate cleavage)
5. Ecdysis
6. Jointed appendages, segmentation, chitin exoskeleton

Question 45

Tagmatization

Answer 45

— Specialization in the body regions of arthropods
— Segmented body & jointed appendages arranged into functional units (= tagmata) with specialized functions (division of labour)
→increase in arthropod diversity!
• head and thorax often merged as cephalothorax

Question 46

Body plans of arthropods
Tagmatization = fusion of segments

Answer 46

Divide arthropods into two groups

Chelicerae:
- Fang like structure for mouth, don’t have antennae

Mandibles:
- Mendibles for mouth and have antennae on the head

Question 47

5 Main Groups of Arthropods
Subphyla

Answer 47

• Trilobita
– trilobites, all extinct
• Chelicerata
– scorpions, spiders, mites, etc.
• Myriapoda
– millipedes, centipedes, etc.
• Crustacea
– crabs, lobsters, shrimp, etc.
• Hexapoda
– springtails, insects, etc.

Kingdom
^
|
Subkingdom
^
|
Superphylum
^
|
Phylum

Kingdom: Metazoa

Subkingdom: Eumetazoa

Superphylum: Deuterostomia + Lophotrochozoa + Ecdysoza

Phylum: Portifera + Ctenophora + Cnidaria + Acoela + Exhinodermata + Chordata + Platyheiminithes + Mollusca + Annelida + Nematoda + Arthropoda

Question 48

KEY CONCEPTS

Answer 48

• Modifications to the body plan through selection have lead to great diversity based on
─ feeding and locomotion
• Evolution resulted in innovation related to ─ respiratory mechanisms
─ excretory systems
─ food capture
─ morphology related to locomotion

Question 49

Deuterostomia
blastopore → anus

Answer 49

• Based on molecular data (~ 4-5 phyla)
– 2 main phyla: Echinodermata and Chordata (they are sister clades. 1 does not evolve from the other)
-represents living organisms not the ones that are extinct

• Some shared developmental characters:
– triploblastic (3 germ layers) (embryo development)
– radial, indeterminate cleavage

• embryos have indeterminate, radial cleavage.
• mesoderm instead forms as outpocketings of the archenteron, forming the coelom (enterocolom) from the space in the outpocketings.
• The blastopore becomes the anus, and the mouth instead forms from a later opening.

Note: chordates did NOT evolve from echinoderms, they share a common ancestor!!

Question 50

Echinoderms and Vertebrate origins

Answer 50

-Chordates have gill slits
-Echino do not = lost that trait —> based on phylogenetic tree

Question 51

Phylum Echinodermata

Answer 51

• sea stars, sea urchins, sea lilies, sea cucumbers

• ~7000 extant species

• very good fossil record since the Cambrian – ~13,000fossilspecies

• Calcareous endoskeleton suited to fossilization

•large diversity, even larger in fossil record
— easier to fossilize b/c have hard exoskeleton

3 synapomorphic characteristics:
1. Radial symmetry in adults

2. Calcareous endoskeleton (contains calcium carbonate) but always covered by a thin soft layer
3. Water vascular system – with tube feet

Question 52

Phylum Echinodermata
Basic characteristics

Answer 52

• Slow, sessile, marine
• Adults: pentaradial symmetry
– penta = 5
• Larvae - bilateral symmetry
- share with

• Mouth at centre of arms and faces down

• Thin epidermis covers endoskeleton (CaCO3)

• Diffuse nervous system with no central brain
-common to other groups of invertebrates

• Typically, both sexes engage in broadcast spawning
– fertilization occurs externally, in open water. By externally realizing gametes out into water

•say their ancestor had bilateral symmetry, hence they are categorized like they are in the phylogenetic tree

• Water vascular system
– network of hydraulic canals branching into extensions called tube feet
– madreporite: small calcified plate with a porous opening in the middle that allows water to flow in and out of system. (Is on top slighty on side, anus not far from it)
-reg flow of H2O across whole vascular system to eat, movements, filter H2O
–water pressure + adhesive→operate tube feet (ampulla + podium)

• Tube feet: locomotion, feeding, detection and gas exchange

Question 53

Main Echinoderm Classes
Class Echinoidea

Answer 53

(urchins, sand dollars)
• Spines: locomotion and protection
• Eat seaweed
-have structures associated with a mouth

Question 54

Main Echinoderm Classes

Answer 54

Class Holothuroidea (sea cucumbers (penta))
• Elongated Symmetry - secondarily bilateral
(Larva is bilateral?)
• Some tube feet around the mouth serve as feeding tentacles
• filter or suspension feeders
-f= filter at bottom of ocean
-S= take nutrients from h2o

Question 55

Main Echinoderm Classes
Class Asteroidea (sea stars)

Answer 55

• Active, walk via tube feet
• Carnivorous predators

Question 56

Phylum Chordata

Answer 56

• Bilateral symmetry
• Deuterostome:
✓triploblastic – 3 germ layers
✓radial, indeterminate cleavage
• Coelom
• Segmented bodies

•cephalochordatas considered the most primitive, basic body plan

Question 57

4 chordate Synapomorphies

Answer 57

1) Notochord (noto = back, chord = cord)
• Cartilaginous skeletal structure
• Flexible rod located dorsally between the digestive tube and the nerve cord
• Stiff but not rigid support along body
• Present in all chordate embryos and some adults
• Most vertebrates - reduced to discs/pads between vertebrae

2) Dorsal hollow nerve cord • unique to chordates
- in other animals, nerve cord is solid and ventral
• develops from neural plate of ectoderm (dorsal to notochord)
• plate rolls into tube during embryonic development
• Nerve cord→spinal cord, nervous system & brain (among vertebrates)

3) Pharyngeal slits/clefts
In most chordates: clefts→pharyngeal slits
─ connects pharynx to external environment
─ allows water to exit w/o continuing through entire digestive tract
Suspension-feeding devices in many invertebrate chordates
Slits and supporting arches modified for gas exchange in vertebrates (“gills slits”)

4) Muscular, post-anal tail
• Most adult chordates have muscular tail
posterior to anus
• Contains muscles and skeletal elements
─ provides propulsive force in many swimming
species
─ acts as rudder, provides balance, grip, etc.
• Reduced in many species during embryonic development

Other Important Character States
• Bilateral symmetry
• Segmentation – what other phyla are also segmented?
• e.g.,muscle segments,vertebral column
— in Arthropoda and annelids —> externally seen
— In Chordata —> seen externally in muscles

Question 58

Phylogenetic Relationship between Echinoderms, Hemichordates &Chordates

Answer 58

Lineages split a long time ago. Most likely in the Cambrian explosion, potentially pre-Cambrian, hence why we look so different.

Question 59

SubPhylums of Chordata

Answer 59

• Includes two groups of invertebrates:
— Subphylum Urochordata
— Sybphylum Cephalochordata

• Includes animals with a backbone (= vertebral column):
— Subphylum Vertebrata

Question 60

Subphylum Cephalochordata

Answer 60

(lancelets) 25 spp., all marine
• Adult has all 4 key synapomorphies of chordates
• Segmentation
─ serial arrangement of muscle ─ cephalization is minimal
• Sedentary suspension feeders

Question 61

Subphylum Urochordata

Answer 61

(tunicates) ~1250 species, all marine
• Larvae stage has all 4 key synapomorphies of chordates
• Adults-donotlooklikechordates
─ metamorphosis→chordate characters
disappear
─ sessile, filter/suspension feeders

Question 62

Subphylum Vertebrata (= Craniata)

Answer 62

• ~ 50,000 extant spp.
• Chordateswithahead
─ cranium = skull
─ more coordinated movement and complex feeding
behaviours
• FossilformsfromChinashowapparent morphological transition from non-craniate to craniate chordates
• Cambrian fossils from Haikou district
— Haikouella: eyes and brain but no braincase
— Haikouichthys about the same size and shape but had a braincase

Question 63

Subphylum Vertbrata
synapomorphies

Answer 63

1) Two or more clusters of Hox genes
• non-craniate chordates have only 1 cluster
• greater genetic & morphological complexity

2) Neural crest
• group of embryonic cells that forms near dorsal margins
of the closing neural tube
• contributes to formation of bones and cartilages of the skull, and other structures

3) Endoskeleton and pronounced cephalization
• brain encased in protective plates (cranium ≈ skull)
• endoskeleton cartilage or bone
4) Elaborate skull – cranium
• Protects central nervous system & key sensory
structures
• Brain with 3 distinct regions

5) Circulatory system modified
• closed circulatory systems
• including a heart with two+ chambers
• Hemoglobin in red blood cells
• oxygenated by passing close to gills or lungs

6) Vertebral column = backbone
▪ a chain of skeletal elements surrounding
and protecting nerve cord
→ More complex nervous system
→ Replaces function of notochord
— providing rigidity
— provides attachment sites for muscles
and other skeletal elements (e.g., ribs)

7) Pharyngeal slits
→function as gill slits (aquatic vertebrates) →parts of braincase or ear (terrestrial vertebrates)

Question 64

Agnatha
Jawless vertebrates = Agnathans

Answer 64

• Vertebrates that lack jaws
• Two extant lineages: Cyclostomes (for some not a monophyletic group)
• More agnathans in the fossil record
• Lack teeth
• long,flexible,tubularbodies
─ but no paired fins
─ skeleton made of cartilage (not bone)

Question 65

Gnathostomata

Jawed Vertebrates = Gnathostomes

Answer 65

• Jawed fish evolved ~450 Mya
─ gnatho = jaw, stoma = mouth
• Have 2 pairs of fins
─ extinct agnathans (jawless) had 1 pair ─ extant agnathans have no paired fins
• Bigger, more developed brain than agnathans
• Further duplication of Hox genes: ─ 2 x 2 = 4 clusters of Hox genes ─ added genetic diversity
— Jaws → diverse feeding behaviour
— larger brain
— improved vision and sense of smell

Why is Hox gene duplication important?
— Greater segmentation of body and greater complexity = allow for greater genetic diversity

Question 66

Where did jaws come from?

Answer 66

• Modifications of 2 pairs of gill arches (=skeletal rods) that used to support anterior pharyngeal slits
• With hinged jaws, more ways of getting food than suspension feeding using pharynx
─ grasp, kill, shred and crush large food items
— allowed modification of feeding = no longer limited too small food
• Posterior slits→specialized for gas exchange (gill slits) in aquatic vertebrates

The significance of jaws
-grooming, carrying young, building nests, allows for more diversity of what can eat

Question 67

Fossil Gnathostomes

Answer 67

• The earliest gnathostomes in the fossil record is an extinct lineage of armored vertebrates called placoderms

• Appeared in the Ordovician- Silurian, at least 450 million years ago

• Had bony exoskeleton but still cartilaginous endoskeleton

Question 68

OVERVIEW OF KEY EVENTS IN VERTEBRATE EVOLUTION

Answer 68

Key innovations
1. Pharyngeal gill slits.
2. Notochord dorsal, hollow nerve cord, post-anal tail
3. Cranium, neural crest, rudimentary, vertebrae, or vertebral column (fossil agnathans (🟠))
3. Jaws, fins. (🟣)
4. Internal skeleton, swim bladder or air breathing Organ (🟢)
5. Loped fins, lungs.
6. Paired limbs.(🔴)
7. Amniotic egg (🔵)

Carboniferous Amniotic egg (🔵)
Devonian Limbs capable of moving on land. (🔴)
Devonian bony endoskeleton (🟢)
Silurian. Jaws (🟣)
Ordovician. Bony exoskeleton (🟠)

Question 69

KEY CONCEPTS

Answer 69

• Deuterostomes are a monophyletic group
• Echinodermatabodyplan
— Radial symmetry in adults, endoskeleton, and water vascular system
• Ancestral Chordate body plan has been retained but modified in diverse lineages
— Duplication of Hox genes led to development of complex body structures including limbs for dynamic locomotion
— Vertebrate evolution shows development of brain, and diversification of feeding methods
— Jaws likely evolved from the pharyngeal slits to aid feeding
• Know the key characteristics in chordate evolution and main groups covered in lecture slides