Download Comparing Invertebrates

Comparing Invertebrates
What is an Animal?

Animals, members of the kingdom
Animalia, are multicellular, eukaryotic
heterotrophs whose cells lack cell walls

Invertebrates are animals that have no
backbone, or vertebral column


Includes over 95% of all animal species
Vertebrates are animals that have a
backbone

Includes 5% of all animal species
Modern Evolutionary Relationships

Cladogram indicating the sequence in which important
invertebrate features evolved
What Animals Do to Survive

Animals carry out the following essential
functions:
1.
2.
3.
4.
5.
6.
7.
Feeding – herbivores, carnivores,
omnivores, detritivores
Respiration – take in O2 and give off CO2
Circulation – diffusion, closed/open
circulatory system
Excretion – ridding the body of liquid and
solid wastes
Response – nervous systems
Movement – sessile or mobile
Reproduction – asexual or sexual
Trends in Animal Evolution

Complex animals tend to have high
levels of cell specialization and internal
body organization, bilateral body
symmetry, a front end or head with
sense organs, and a body cavity
Trends in Animal Evolution
mollusks
echinoderms
roundworms
flatworms
cnidarians
sponges
annelids arthropods
chordates
Early Development

Animals that reproduce sexually begin life
as a zygote (fertilized egg)



The zygote undergoes a series of divisions
(cleavage) to form a blastula (hollow ball of cells)
 The blastopore leads to a central tube that
becomes the digestive tract
A protostome is an animal whose mouth is formed
from a blastopore (most invertebrates)
A dueterostome is an animal whose anus is formed
from the blastopore (most vertebrates)
Body Symmetry

With the exception of sponges, all
animals exhibit some type of body
symmetry
 Radial symmetry: body plan in
which body parts repeat around
the center of the body

Bilateral symmetry: body plant
in which only a single imaginary
line can divide the body into 2
equal parts
Cephalization

Animals with bilateral
symmetry usually
exhibit what is called
cephalization
 Cephalization is the
concentration of
sense organs and
nerve cells at the
anterior, or front,
end of the body
Evolutionary Trends

Specialized Cells, Tissues, and Organs


The evolution of larger and more complex
animals involved specialized cells joining
together to form tissues, organs, and
organ systems
Body Symmetry

All invertebrates except sponges exhibit
some type of body symmetry



Asymmetry: sponges
Radial: cnidarians and echinoderms
Bilateral: worms, mollusks, and arthropods
Evolutionary Trends

Cephalization


The evolution of a body plan for feeding,
defense, and other functions was
accompanied by the trend toward
cephalization
Invertebrates with cephalization can
respond to the environment in more
sophisticated ways than simpler
invertebrates
Evolutionary Trends

Segmentation


Most inverts with bilateral symmetry also
have segmented bodies specialized for
specific functions
Coelom Formation


A coelom is a body cavity that forms
between germ layers
Most complex animal phyla have a true
coelom that is lined completely with
mesoderm
About the Coelom

Coelom means body cavity (a tube within a tube).



Acoelomates

Have NO TRUE body cavity!
Pseudocoelomates

Have a fluid filled cavity BUT – it is not lined like that of higher-order animals.
Coelomates

Have a body cavity that separates the body into an inner and outer tube (fully lined).
Coelom Formation
pseudocoelom
digestive cavity
digestive tract
coelom
digestive tract
acoelomate
pseudocoelomate
coelomate
KEY TERMS TO KNOW
Early Development
During early development,
the cells of most animal
embryos separate into
three layers called germ
layers:
1.
2.
3.
ENDODERM: innermost
layer; develops into the
lining of the digestive tract
& much of the respiratory
system
MESODERM: middle
layer; develops into
muscles and much of the
circulatory, reproductive,
and excretory systems
ECTODERM: outermost
layer; develops into the
sense organs, nerves, and
outer layer of the skin
Evolutionary Trends

Early Development

In most inverts, the zygote divides
repeatedly to form a blastula (a hollow
ball of cells)


In protostomes, the opening of the blastula
(blastopore) develops into a mouth
 Includes worms, arthropods, and mollusks
In deuterostomes, the blastopore forms an anus
 Includes echinoderms and deuterostomes
KEY TERMS TO KNOW

Early Development

Protostomes are
organisms that
develop a mouth first
and then an anus.


Most invertebrates are
protostomes
Deuterostomes are
organisms that
develop an anus first
and then a mouth.

Echinoderms and all
vertebrates are
deuterostomes
Form and Function in Inverts

Feeding and Digestion

The simplest animals break down food
primarily through intracellular digestion


Food is digested in the cells
More complex animals use extracellular
digestion

Food is broken down outside the cells in a
digestive cavity and then absorbed into the
body
Patterns of Extracellular Digestion


Simple animals such as cnidarians and
flatworms ingest food and expel wastes
through a single opening
More complex animals digest food in a tube
called the digestive tract


Food enters mouth and wastes leave through the
anus
These are characteristics of a one way digestive
tract

Roundworms, annelids, mollusks, arthropods,
echinoderms
Patterns of Extracellular Digestion
Form and Function in Inverts

Respiration


Respiratory organs have large surface
areas that are in contact with the air or
water
For diffusion to occur, the respiratory
surfaces must be moist
Aquatic v/s Terrestrial Respiration




Many aquatic animals respire through
their skin (cnidarians and flatworms)
Aquatic mollusks, arthropods, and
annelids exchange gases through gills
Spiders respire using book lungs
In insects, air enters the body through
openings called spiracles, travels
through tracheal tubes and then diffuses
in and out of surrounding fluids
Invertebrate Respiratory Structures
Form and Function in Inverts

Circulation

Most complex animals move blood through
their bodies using one or more hearts and
either an open or closed circulatory system

OPEN: blood is only partially contained within a
system of blood vessels


Arthropods and most mollusks
CLOSED: vessels extend throughout the body
and blood remains contained within these
vessels

Annelids and some mollusks
Open v/s Closed Circulatory System
Form and Function in Inverts

Excretion



Most animals have an excretory system that rids
the body of metabolic wastes while controlling the
amount of water in the tissues
Aquatic: ammonia diffuses from the body tissues
into the surrounding water
Terrestrial: convert ammonia into urea before
elimination


In annelids and mollusks, urine forms in tube-like
structures called nephridia
Some insects and arachnids have Malpighian tubules
(saclike organs that convert ammonia into uric acid)
Invertebrate Excretory Systems
Form and Function in Inverts

Response: Inverts show 3 trends in the
evolution of the nervous system:
1.
2.
3.
Centralization – in flatworms and roundworms,
the nerve cells are more concentrated, or
centralized with a few clumps of ganglia (nerve
tissue) in the head
Cephalization – in mollusks and arthropods,
ganglia are organized into a brain at one end of
the body that controls the nervous system
Specialization – complex animals, such as
insects and echinoderms, have a variety of
specialized sense organs that detect light,
sound, chemicals, and movement
Invertebrate Nervous Systems
Form and Function in Inverts

Movement & Support: invertebrates have
one of 3 main kinds of skeletal systems
1.
Hydrostatic skeleton: muscles surround a fluid
filled body cavity that supports the muscles

2.
Exoskeleton: external body covering made of
chitin

3.
Annelids & some cnidarians
arthropods
Endoskeleton: structural support located inside
the body

Echinoderms and vertebrates
Form and Function in Inverts

Reproduction: most invertebrates reproduce
sexually during at least part of their life cycle


Many, however, may also reproduce asexually
Sperm and egg may meet in 2 ways:


External fertilization: eggs are fertilized outside
the female’s body (usually in water)
Internal fertilization: eggs are fertilized inside the
female’s body
“Radiata”
Eumetazoa
Metazoa
Ancestral colonial
flagellate
Deuterostomia
Protostomia
Bilateria
Nematoda
Nemertea
Rotifera
Arthropoda
Annelida
Mollusca
Platyhelminthes
Chordata
Echinodermata
Brachiopoda
Ectoprocta
Phoronida
Ctenophora
Cnidaria
Porifera