Lec 10

Animals are:

multicellular

Animals are:

• multicellular

• heterotrophic

• eukaryotes

• with layers of tissues

Heterotrophs ingest other organisms

Do only animals have nerve tissue?

Yes, only animals have nerve tissue

Their bodies are held together by structural proteins

Like collagen

Animals have

been around for

more than a billion

years

The kingdom has

a huge diversity of

living species

– And an even

greater diversity

of extinct ones

After a sperm fertilizes an egg

A zygote is formed

– The zygote undergoes cleavage

– forming a ball of cells called a blastula

The blastula then forms a hollow embryo called a

gastrula

An embryo folds inward, producing the

ectoderm (outer layer) and the

endoderm (inner layer).

The common ancestor of all living animals

– Probably lived 1 billion years ago

– Probably resembled some modern protists

Colonial protist,

A cluster of

identical cells

Some of the earliest animals are the Ediacaran

fauna

– Discovered first in Australia

– they were all soft-bodied and small

The Cambrian explosion was the first appearance

of the major groups of living animals

– Including the first predators and prey

Many of these died out in

a mass extinction

When did this take place?

540 Million Years Ago

When was the Mesozoic Era

(250–65 Million Years Ago)

Our era began with the mass

extinctions of most animals.

Modern groups of mammals and insects

diversified rapidly during this time.

when was The Cenozoic Era 

(65 Million Years Ago to the Present)

Some have radial symmetry like a flower pot.

What is this?

Any slice through

the central axis

divides the animal

into mirror images.

Others have bilateral symmetry

two-sided symmetry

What is this?

Only one cut can

divide the animal

into mirror-image

halves.

Bilaterally symmetrical animals have

– A dorsal (top) side and a ventral (bottom) side

– A right and left side

– Anterior (head) and posterior (tail) ends

– Cephalization, the development of a head

What are Tissues:

collections of specialized cells

– isolated from other tissues by membranes

Diploblastic animals

– Have two tissue layers

– These animals split early from the other groups

Triploblastic animals

– Have three tissue layers

– Include most of the animals we all know

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The Cambrian explosion was the first appearance

of the major groups of living animals

– Including the first predators and prey

Many of these animals died

out in a mass extinction

Zoologists currently recognize about 35 major groups

or phyla of animals

Invertebrates

are animals that lack a backbone

– They are 95% of known animal species

Sponges, phylum Porifera split off first

-They are different from all other animals

There are more than 5000 described sponge species

Sponges 

– Live in both fresh and salt water

• They are sessile

• They have a porous body

• Lack true tissues and organs

Their bodies are structured with silica fibers

called

 spicules

Most sponges are hermaphrodites

– each individual is both male and female

– And they can reproduce sexually or asexually.

Sponges are filter feeders

By beating flagella, the

choanocytes create current

Food particles are trapped

in the mucus, engulfed, and digested

Amoebocytes

transport nutrients to other cells

All other animals except sponges belong to the

clade Eumetazoa,

– animals with true tissues

Most animals are in the clade Bilateria

These are triploblastic

And split into three branches:

Jellies: phylum Cnidaria

Cnidarians were among the earliest eumetazoans

– Have a wide range of sessile and floating forms

– They have a diploblastic body

The body of a cnidarian

– Is a sac with a central digestive compartment,

the gastrovascular cavity

• A single opening acts as both mouth and anus

There are about 10,000 described cnidarian species

They have radial symmetry

There are two variations on this body plan

The sessile polyp

– and the floating medusa

All cnidarians are carnivores

They are armed with tentacles and cnidocytes

for capturing prey

The phylum Cnidaria has four major classes:

Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa

Many jellies are bioluminescent.

The largest are more

than 100 m long

In the class Scyphozoa

Jellies (medusae) are the prevalent

form of the life cycle

the class Cubozoa includes deadly sea wasps

– whose poison is more potent than cobra venom.

Class Anthozoa includes the corals

and sea anemones

– They occur only as polyps

Most animal species belong to the clade

Bilateria, which have bilateral symmetry and

triploblastic development

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The simplest are Flatworms: phylum Platyhelminthes

Live in water and in damp terrestrial habitats

– They are acoelomate:

– they have no body cavity

– and no vascular system

Rotifers,

Are tiny animals that inhabit water and damp soil

– They are one type of plankton

Rotifers are smaller than many protists

– But they are multicellular, with organs like ours

– they mate by hypodermic impregnation

Bryozoans or Ectoprocts

– Are called moss

animals

Nemerteans

– Are called proboscis worms

Molluscs, Phylum Mollusca

– Includes snails, slugs, oysters, clams,

octopuses and squids

• Most molluscs are marine

All molluscs have a similar body plan with three

main parts:

– A muscular foot

– A visceral mass

– A mantle

About three-quarters of all living mollusc species

belong to class Gastropoda

– They have a single, spiraled shell

True or False

Slugs are gastropods whose ancestors had

shells

True

Molluscs of class Bivalvia

– Include many species of clams, oysters,

mussels, and scallops

– Have a shell divided into two halves

The visceral mass has gills for feeding and breathing

Class Cephalopoda includes squids and

octopus

– Carnivores with beaks surrounded by tentacles

of their modified foot

Squids use their siphon

– To fire a jet of water, which allows them to

swim very quickly

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Annelids are segmented worms, their bodies are

a series of repeating units.

Polychaete worms

 Have bristles that function as gills and aid

locomotion

The Phylum Arthropoda

Arthropods are also segmented coelomates

• Two out of every three known species of

animals are arthropods

• They are found in nearly all habitats of the

planet

Cheliceriforms

Are named for clawlike feeding appendages

called chelicerae

–(you might call them fangs)

Arachnid bodies have 2 main segments:

• an abdomen and a cephalothorax

Millipedes

• Have a large number of legs, two per segment

• Centipedes

–Are carnivores with jaw-like mandibles

–Have one pair of legs per segment

Insects: the most successful animals

–Are more diverse than all other forms of

animal life combined

–They live in almost every terrestrial habitat

The anatomy of an insect:

Metamorphosis occurs during a pupal stage

Larva (caterpillar)

Pupa Pupa

Emerging adult

Adult

Decapods 

are all relatively large crustaceans

–And include lobsters, crabs, crawfish, and shrimp

Planktonic crustaceans include copepods

–Which are among the most numerous of all

animals

Echinoderms have a water vascular system

–A network of hydraulic canals

–for locomotion, feeding, and gas exchange

Brittle stars have a distinct central disk

– And long, flexible arms

Sea urchins and sand dollars have no arms

– But they do have five rows of tube feet that

function in movement

In the Cambrian period, 540 million years ago

A huge variety of animals inhabited Earth’s oceans

One of these animals gave rise to chordates, one of the

most successful groups of animals

Chordates

–Phylum Chordata, the phylum to which

humans belong

–includes some invertebrates

–and the vertebrates

Chordates have grooves in the neck called

pharyngeal pouches

Used for breathing in aquatic vertebrates

– they develop into parts of the neck in terrestrial

vertebrates.

All chordates share these characters:

Tunicates or Sea Squirts

–Are marine animals

–Are the earliest branch of chordates

Tunicates most resemble other chordates during

their “tadpole” larval stage

An adult tunicate draws in water through a siphon,

filtering food

Lancelets,

– Are named for their bladelike shape

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Craniates are chordates with a skull

Cephalization opened up a new way of feeding for

chordates: predation

The most primitive surviving craniates are the

hagfishes

Vertebrates

Get their name from vertebrae, the series

of bones that make up the backbone

There are about 52,000 species of vertebrates

Vertebrates have:

–Vertebrae enclosing a spinal cord

–An elaborate skull

Vertebrates have:

–Vertebrae enclosing a spinal cord

–An elaborate skull

–Fin rays (in aquatic forms),

–or limb bones (that evolved from these fin rays)

Lampreys

• the oldest living group of vertebrates

–Have cartilage vertebrae

–And no jaws

Cartilaginous fishes have a soft skeleton

• Interestingly the cartilaginous skeleton

–Evolved secondarily from a mineralized

skeleton

The vast majority of vertebrates – 40,000 species

–Belong to a group called Osteichthyes or bony

fishes.

Tetrapods are bony fishes with limbs and feet.

• At some point in vertebrate history the fins of

some lobe-fins evolved into the limbs and feet of

tetrapods

Amphibians

Class Amphibia

– has about 5,000 species

– Amphibians have moist skin that

complements the lungs in breathing

Amphibian means “two lives”

Order Anura

– Includes frogs and toads, which lack tails

And caecilians

– which are legless and resemble worms

Reptiles

Have scales that create a waterproof barrier

– Lay shelled eggs on land

Their amniotic eggs contain specialized

membranes that protect the embryo.

includes – lizards& snakes, – turtles,

– crocodilians, – the extinct dinosaurs, 

– And birds!

Most reptiles are ectothermic

– Absorbing external heat as the main source of body

heat

• Birds are endothermic

– Capable of keeping the body warm through

metabolism

The oldest reptilian fossils date to about 300

million years

And birds are archosaurs too!

– But almost every part of their reptile anatomy has

been modified for flight

Birds probably descended from theropods

– bipedal, carnivorous dinosaurs

By 150 million years ago

– Feathered theropods had evolved into birds

• Archaeopteryx is the oldest bird known

The ratites

– Are all flightless: emus, ostriches and rheas

Lecture 14: Mammals and Genes

 Mammals, class Mammalia have more than 5,000 living species

Mammals originated about 225 million years ago
 

What are they named for?

Mammary glands

• Hair

• A larger brain than other vertebrates of

equivalent size

Monotremes

Are a small group of egg-laying mammals

– including the echidna or spiny anteater

Marsupials

A marsupial is born very early in its development

– And completes its embryonic development whilenursing within a pouch called a marsupium

Include opossums,kangaroos, and

koalas

Eutherian

 also called placental mammals

mammals have a longer period of

pregnancy.

• Eutherians complete their embryonic

development within a uterus

• joined to the mother by the placenta – a

combination of the mother’s and baby’s tissue

Genetics

– Is the scientific study of heredity

Heredity

– Is the transmission of traits from one generation to

the next

– Offspring differ somewhat in appearance from

parents and sibling

Before cell division

– The DNA in each chromosome uncoils and gets

replicated in a process called 

Synthesis

DNA molecules are packaged into structures

called

chromosomes

In humans

–Somatic cells (typical body cells) have 46

Unlike somatic cells

–Gametes are haploid cells, containing only

23 chromosomes

–Half of each pair

Where are sex cells produced?

In the gonads

in a process called

meiosis

somatic cells are

divided into gametes

In sexual reproduction

– Two parents produce offspring that have unique

combinations of genes from both parents

Homologous chromosomes

Are the two chromosomes composing a pair

– We get one of each pair from each parent

– They contain the same genes – so they control the same traits.

This genetic variation is the raw material for

evolution.

Gregor Mendel (1822-1884)

Discovered the mechanisms of

inheritance: Mendelian genetics

Mendel was the first person able to explain this

3:1 inheritance pattern

Before Mendel the major explanation of heredity

was a “blending” hypothesis

The idea that genetic material contributed by two

parents mixes in the that way blue and yellow paints

blend to make green

Mendel figured out that we pass on discrete

heritable units of information called genes.

Mendel discovered an interesting thing:

–The white trait disappears when you cross purple

with white – but reappears in the next generation

First, there are alternative versions of genes

– now called alleles

– two alleles are necessary to produce each trait

If the two alleles for a gene differ

– Then one, the dominant allele, determines the

organism’s appearance

– The other allele, the recessive allele, has no

noticeable effect on the organism’s appearance

An organism’s phenotype

– Is its physical appearance

An organism’s genotype

– Is its genetic makeup

An organism that is homozygous for a particular

gene

– Has a pair of identical alleles for that gene

An organism that is heterozygous

– Has a pair of alleles that are different for that gene

A testcross

–Crosses an individual with the dominant

phenotype with an individual that is

homozygous recessive

–This allows us to determine the genotype of

an individual with the dominant phenotype

A Punnett square