Comparing Invertebrates
Chapter 29
Invertebrate Evolution
Chapter 29-1
29-1 Invertebrate Evolution
Origins of Invertebrates

Early animals were flat, soft bodied organisms that
lived on the bottom of shallow seas.
•
•

Segmented with bilateral symmetry.
NO cell specialization.
Recently scientists discovered microscopic fossils
that are 610-570 million years old.
•
Seem to be developing embryos of early multi-cellular
organisms.
29-1 Invertebrate Evolution
The First Multicellular Animals



Ediacaran Fossils found in China
610 to 570 Million Years old
They are the ancestors of today’s
multicellular animals
29-1 Invertebrate Evolution
The First Multicellular Animals

The fossils:
• were flat and plate shaped
• were segmented
• had bilateral symmetry
• lived on the bottom of shallow seas
• were made of soft tissues
• absorbed nutrients from the surrounding
water
29-1 Invertebrate Evolution
Invertebrate Phylogeny

Many features of modern invertebrates
evolved during the Cambrian period
such as:
• tissues and organs
• patterns of early development
• body symmetry
• cephalization
• segmentation
• formation of three germ layers and a coelom
29-1 Invertebrate Evolution
Invertebrate Phylogeny

Invertebrate Evolutionary Relationships
29-1 Invertebrate Evolution
Invertebrate Phylogeny
Roundworms
Flatworms
Cnidarians
Sponges
Unicellular ancestor
29-1 Invertebrate Evolution
Invertebrate Phylogeny
29-1 Invertebrate Evolution
Invertebrate Phylogeny
29-1 Invertebrate Evolution
Invertebrate Phylogeny

Invertebrate Evolutionary Relationships
29-1 Invertebrate Evolution
Evolutionary Trends

Specialized cells, Tissues, and Organs
• Sponges - 1st with specialized cells
• Jelly fish - 1st with muscle tissue
• Flatworms - 1st with organs

Body Symmetry
• Asymmetrical (no symmetry) – Sponges
only
• Radial – Jellyfish and Echinoderms
• Bilateral – Flatworms, Roundworms,
Annelids, arthropods, and Mollusks
29-1 Invertebrate Evolution
Evolutionary Trends
• Cnidarians and echinoderms exhibit radial
symmetry where parts extend from the center of
the body.
Radial symmetry
Planes of
symmetry
29-1 Invertebrate Evolution
Evolutionary Trends
• Worms, mollusks, and arthropods exhibit bilateral
symmetry, or have mirror-image left and right
sides.
Bilateral symmetry
29-1 Invertebrate Evolution
Evolutionary Trends

Cephalization
• Cephalization is the concentration of sense
organs and nerve cells in the front of the body.
• Invertebrates with cephalization can respond to
the environment in more sophisticated ways
than can simpler invertebrates.
•
•
•
•
None: Sponges
Nerve Net: Cnidarians
Ganglia: Worms, Clams, Echinoderms
Brains: Cephalopod Mollusks, Arthropods
29-1 Invertebrate Evolution
Evolutionary Trends
 Segmentation
• Over the course of evolution, different
segments in invertebrates have often become
specialized for specific functions.
• Segmentation allows an animal to increase its
size with minimal new genetic material.
29-1 Invertebrate Evolution
Evolutionary Trends
•Coelom Formation
• Flatworms are acoelomates. This means they have no
coelom, or body cavity, that forms between the germ
layers.
Ectoderm
Mesoderm
Digestive
cavity
Acoelomate
Endoderm
29-1 Invertebrate Evolution
Evolutionary Trends

Pseudocoelomates have a body cavity lined
partially with mesoderm.
Pseudocoelom
Digestive tract
Pseudocoelomate
29-1 Invertebrate Evolution
Evolutionary Trends
• Most complex animal phyla have a true
coelom that is lined completely with tissue
derived from mesoderm.
Coelom
Digestive tract
Coelomate
29-1 Invertebrate Evolution
Evolutionary Trends
29-1 Invertebrate Evolution
Evolutionary Trends
• Embryological Development
• In most invertebrates, the zygote divides to form a
blastula—a hollow ball of cells.
29-1 Invertebrate Evolution
Evolutionary Trends


In most worms and arthropods, nerve
cells are arranged in structures called
ganglia.
In more complex invertebrates, nerve
cells form an organ called a brain.
29-1 Invertebrate Evolution
Evolutionary Trends
29-1 Invertebrate Evolution
Evolutionary Trends
Invertebrate Form &
Function
Chapter 29-2
The End
29-2 Form and Function in Invertebrates
Feeding and Digestion

Intracellular: Food
digested by cells and
passed around by diffusion.
(ex: sea anemone)
• Extracellular: food
broken down in
cavity and then
absorbed. (ex: earthworm)
29-2 Form and Function in Invertebrates
Feeding and Digestion

Feeding and Digestion
• The simplest animals break down food
primarily through intracellular digestion. More
complex animals use extracellular digestion.
29-2 Form and Function in Invertebrates
Feeding and Digestion


When food is digested inside cells, this
process is known as intracellular
digestion.
Sponges use intracellular digestion.
29-2 Form and Function in Invertebrates
Feeding and Digestion



In extracellular digestion, food is
broken down outside the cells in a
digestive cavity or tract and then
absorbed into the body.
Mollusks, annelids, arthropods, and
echinoderms rely almost entirely on
extracellular digestion.
Flatworms and cnidarians use both
intracellular and extracellular digestion.
29-2 Form and Function in Invertebrates
Feeding and Digestion


Cnidarians and most flatworms ingest
food and expel wastes through a single
opening.
Food is digested in a cavity through both
extracellular and intracellular means.
29-2 Form and Function in Invertebrates
Feeding and Digestion
Mouth/anus
Gastrovascular cavity
Digestive
cavity
Cnidarian
Pharynx
Mouth/anus
Flatworm
29-2 Form and Function in Invertebrates
Feeding and Digestion


In more-complex animals, food enters
the mouth and wastes leave through the
anus.
A one-way digestive tract often has
specialized regions.
29-2 Form and Function in Invertebrates
Intestine
Feeding and
Digestion
Gizzard
Crop
Pharynx
Mouth
Annelid
Anus
Pharynx
Crop
Anus
Arthropod
Mouth
Stomach and
digestive glands
Rectum
Intestine
29-2 Form and Function in Invertebrates
Respiration
• All respiratory systems have two basic requirements:
• a large surface area that is in contact with the air or
water
• the respiratory surfaces must be moist for diffusion to
occur
29-2 Form and Function in Invertebrates
Respiration

Aquatic invertebrates:
 Require moist respiratory
surfaces
 Some through the pores
of the skin
 Some through gills (large
feathery structure rich in
blood vessels)
29-2 Form and Function in Invertebrates
Respiration
• Aquatic Invertebrates
• Gills are feathery structures that expose a large
surface area to the water.
29-2 Form and Function in Invertebrates
Respiration

Terrestrial Invertebrates:
Book Lungs
 Covered by water or mucus
inside the body.
 Book lungs – spiders
 Spiracles - other insects
Spiracles
29-2 Form and Function in Invertebrates
Respiration
• Terrestrial Invertebrates

Grasshoppers and other insects have
spiracles and tracheal tubes.
29-2 Form and Function in Invertebrates
Circulation

Most complex animals have one or
more hearts to move blood through
their bodies and either an open or
closed circulatory system
29-2 Form and Function in Invertebrates
Circulation

Open – blood partially contained in vessels

Closed – blood forced through vessels
29-2 Form and Function in Invertebrates
Circulation
• Open Circulatory Systems
• In an open circulatory system, blood is only
partially contained within a system of blood
vessels.
• One or more hearts or heartlike organs pump blood
through blood vessels into a system of sinuses, or
spongy cavities.
• The blood makes its way back to the heart.
29-2 Form and Function in Invertebrates
Circulation

Open circulatory systems are
characteristic of arthropods and most
mollusks.
29-2 Form and Function in Invertebrates
Circulation
• Closed Circulatory Systems
• In a closed circulatory system, a heart or
heartlike organ forces blood through vessels that
extend throughout the body.
• Materials reach body tissues by diffusing across
the walls of the blood vessels.
• Closed circulatory systems are characteristic of
larger, more active animals.
29-2 Form and Function in Invertebrates
Circulation

Among the invertebrates, closed circulatory systems
are found in annelids and some mollusks.
Heartlike structure
Small vessels in tissue
Blood vessels
Annelid: Closed
Circulatory System
Heartlike structures
29-2 Form and Function in Invertebrates
Excretion
• Most animals have an excretory system
that rids the body of metabolic wastes
while controlling the amount of water in
the tissues.
• In aquatic invertebrates, ammonia
diffuses from their body tissues into the
surrounding water.
29-2 Form and Function in Invertebrates
Excretion

Aquatic invertebrates:
• Diffusion: aquatic mollusks, sponges, and jelly fish
Mollusk examples
• Flame cells: flatworms
29-2 Form and Function in Invertebrates
Excretion

Terrestrial Invertebrates
• Convert ammonia to urea
to conserve water
• Nephridia: Terrestrial mollusks
and earthworms
• Malpighian tubules: insects
and spiders
29-2 Form and Function in Invertebrates
Excretion

Flatworms use a network of flame cells to
eliminate excess water.
Flame Cells
Excretory
tubules
Flame Cell
Flatworm
Excretory tubule
29-2 Form and Function in Invertebrates
Excretion

In annelids and mollusks, urine forms in
tubelike structures called nephridia.
Nephrostome
Excretory pore
Annelid
Nephridia
29-2 Form and Function in Invertebrates
Excretion



Fluid enters the nephridia through
openings called nephrostomes.
Urine leaves the body through excretory
pores.
Urine is highly concentrated, so little
water is lost.
29-2 Form and Function in Invertebrates

Some insects and arachnids have Malpighian
tubules, saclike organs that convert ammonia
into uric acid.
Excretion
Digestive tract
Arthropod
Malpighian
tubules
29-2 Form and Function in Invertebrates
Excretion


Uric acid and digestive wastes combine
to form a thick paste that leaves the
body through the rectum.
The paste helps to reduce water loss.
29-2 Form and Function in Invertebrates
Response
•Invertebrates show three trends in
the evolution of the nervous system:
centralization, cephalization, and
specialization.
29-2 Form and Function in Invertebrates
Response

Nerve Nets: individual nerve cells in a net-like
formation.

Ganglia: Centralized nerve cells connected to the
nerve net.

Brain: Highly organized ganglia connected to
nerve net.

Specialization: when cells have a special job (ex:
eyespots, eyes, chemical receptors, etc.)
29-2 Form and Function in Invertebrates
Response
• Centralization and Cephalization
• Cephalization is the concentration of nerve tissue
and organs in one end of the body.
29-2 Form and Function in Invertebrates
Response
• Specialization
• The more complex an animal’s nervous system is,
the more developed its sense organs tend to be.
• Complex animals may have a variety of specialized
sense organs that detect light, sound, chemicals,
movement, and electricity.
29-2 Form and Function in Invertebrates
Response

Cnidarians have nerve
nets which consist of
individual nerve cells
that form a netlike
arrangement throughout
the animal’s body.
Nerve cells
Cnidarian
29-2 Form and Function in Invertebrates
Response


In flatworms and
roundworms, the
nerve cells are
more centralized.
There are a few
clumps of nerve
tissue, or ganglia,
in the head.
Ganglia
Flatworm
29-2 Form and Function in Invertebrates
Response
Brain

In cephalopod
mollusks and
arthropods,
ganglia are
organized into a
brain.
Ganglia
Arthropod
Brain
Mollusk
29-2 Form and Function in Invertebrates
Movement and Support


Most animals use muscles to move,
breathe, pump blood, and perform other
life functions.
In most animals, muscles work together
with some sort of skeletal system that
provides firm support.
29-2 Form and Function in Invertebrates
Movement and Support

Hydrostatic skeleton: muscles surround
a fluid-filled body cavity.

Exoskeleton: Arthropods: Hard body
covering made of chitin.

Endoskeleton: Echinoderms: internal
structural support.
29-2 Form and Function in Invertebrates
Movement and
Support
• Hydrostatic
Circular muscles
contracted
Skeleton
Water
Longitudinal
muscles
contracted
Water
29-2 Form and Function in Invertebrates
Movement and
Support
• Exoskeleton
Flexed joint
Extended joint
29-2 Form and Function in Invertebrates
Movement and
Support
• Endoskeleton
Skeletal plates
Tube foot
29-2 Form and Function in Invertebrates
Sexual & Asexual Reproduction

Sexual reproduction maintains genetic
diversity in a population.

Asexual reproduction allows animals to
reproduce rapidly and take advantage of
favorable conditions in the environment.
29-2 Form and Function in Invertebrates
Sexual & Asexual Reproduction

Sexual reproduction is the production
of offspring from the fusion of gametes.

Male and female gametes join to create
a zygote.

The zygote grows through mitosis and
develops into a multicellular animal.
29-2 Form and Function in Invertebrates
Sexual & Asexual Reproduction

In most animals, each individual is a single
sex. (male of female)

The individual produces either sperm or eggs.

Some animals are hermaphrodites—individuals
that produce both sperm and eggs.
29-2 Form and Function in Invertebrates
Sexual & Asexual Reproduction

In external fertilization, eggs are
fertilized outside the female’s body.

In internal fertilization, eggs are
fertilized inside the female’s body.
29-2 Form and Function in Invertebrates
Sexual & Asexual Reproduction

The offspring of asexual reproduction
grow into multicellular organisms by
mitosis of diploid cells.

Some animals reproduce asexually
through budding or by dividing in two.
29-2 Form and Function in Invertebrates
Reproduction

Most invertebrate reproduce sexually to
increase genetic diversity.

BUT….in certain conditions they will
reproduce asexually in order to ensure
continuation of species.