Chapter 23
Section 1 –
Section 2 –
Section 3 –
Section 4 –
Section 5 –
Section 6 –
Section 7 –
Section 8 –
Section 9 –
Invertebrate Diversity
Diverse animals share several key
characteristics
Sponges are relatively simple animals with porous
bodies
Cnidarians are radial animals with stinging cells
Flatworms are the simplest bilateral animals
Roundworms and rotifers have complete digestive
tracts
Annelida are segmented worms
Mollusks show diverse variations on a common
body form
Echinoderms have spiny skin and a water vascular
system
Animal diversity “exploded” during the Cambrian
period
What Is an Animal?

More than a million living species of animals are
organized into about 35 major groups (phyla).



Animals share four key characteristics:
 1. Animals are eukaryotic.
 2. Animal cells lack cell walls.
 3. Animals are multicellular.
 4. Animals are heterotrophs that ingest food.
The fourth characteristic refers to how animals obtain
nutrition  most animals take food into their bodies and
digest it there (called ingestion).
The life cycles of most animals are also different
from those of other organisms, especially in the
early stages of development.
Invertebrates and Vertebrates

One common way to group various animals is
based on whether they have a backbone.



Invertebrates make up approximately 95 percent
of the different kinds of animals on Earth.


INVERTEBRATES: animals without a backbone
VERTEBRATES: animals with a backbone
Most invertebrates live in aquatic or moist
terrestrial habitats.
 The majority of aquatic invertebrate species live in
marine waters (sea stars, jellyfish, worms, etc.)
Vertebrates make up the remaining 5% of
animals found within the animal population.

They live in terrestrial environments as well as
marine and freshwater habitats.
Chapter 23
Section 1 –
Section 2 –
Section 3 –
Section 4 –
Section 5 –
Section 6 –
Section 7 –
Section 8 –
Section 9 –
Invertebrate Diversity
Diverse animals share several key
characteristics
Sponges are relatively simple animals with porous
bodies
Cnidarians are radial animals with stinging cells
Flatworms are the simplest bilateral animals
Roundworms and rotifers have complete digestive
tracts
Annelida are segmented worms
Mollusks show diverse variations on a common
body form
Echinoderms have spiny skin and a water vascular
system
Animal diversity “exploded” during the Cambrian
period
The Body of a Sponge

Sponges (phylum Porifera) are the simplest animals.
Definition: member of a group of animals that lack
true tissues and organs
Unlike most animals, sponges lack true tissues and organs.
Most of the different types of cells in a sponge are
relatively unspecialized.
The body of most sponges consists of two layers of cells
separated by a jelly-like material.
 The outer layer of cells protects the interior of the
sponge and also has many pores through which water
can enter the sponge.
 The inner layer of cells (collar cells) lines the central
cavity of the sponge.
 Definition: flagellated cell in a sponge's inner layer






In the jelly-like material are cells (amoebocytes) that
pick up food from the collar cells, digest it, and carry the
nutrients to other cells.
 Definition: cell found in sponges and other animals
that may digest and distribute food, dispose of
wastes, and change into other cell types
STRUCTURE: In addition to picking up food, amoebocytes
also transport oxygen, dispose of wastes, and can change into
other cell types, such as support structures.



In some sponges, this support can be rigid.
In other sponges, the structures are composed of a
flexible protein called spongin.
DIET: Water moves into the sponge through the pores and
into the central cavity. While the water flows, it is filtered for
food particles and amoebocytes engulf those particles and
transport them to other cells. The water exits through the
large opening at one end of the sponge.
FIGURE 23-4

REPRODUCTION: Sponges live singly or in clusters formed
by budding  budding is a form of asexual reproduction
in which new sponges develop from an outgrowth of a parent
organism.
 Small fragments of a sponge body can grow into an
entire new sponge.


Sponges can also reproduce sexually – the union of
egg and sperm cells form zygotes that develop into
flagellated larvae.
MOVEMENT: Adult sponges are sessile.


Definition: anchored in place
Sponges have chemical defenses that protect them
from possible predators, disease organisms, and parasites.
 These defenses include toxins that keep predators from
eating the sponges and powerful antibiotics that fight
bacterial infections.
Diversity of Sponges

The 9,000 known species of sponges are diverse in
shape, size, and color.


Some sponges consist of a single cylinder, while other
sponges branch out irregularly over the seafloor or lake
bottoms.
Some sponges are quite small, while others can reach
heights of 2 meters.
Chapter 23
Section 1 –
Section 2 –
Section 3 –
Section 4 –
Section 5 –
Section 6 –
Section 7 –
Section 8 –
Section 9 –
Invertebrate Diversity
Diverse animals share several key
characteristics
Sponges are relatively simple animals with porous
bodies
Cnidarians are radial animals with stinging cells
Flatworms are the simplest bilateral animals
Roundworms and rotifers have complete digestive
tracts
Annelida are segmented worms
Mollusks show diverse variations on a common
body form
Echinoderms have spiny skin and a water vascular
system
Animal diversity “exploded” during the Cambrian
period
The Body of a Cnidarian

Two characteristics that all cnidarians share are
radial symmetry and tentacles with stinging
cells.


EXAMPLE: the hydra (commonly found in ponds and
lakes) has a cylindrical body (about 3 cm long) with
projections called tentacles at one end.


Definition: member of a group of invertebrates with
radial symmetry and tentacles with stinging cells
Other cnidarians include jellyfish, sea anemones, and
coral animals.
STRUCTURE: All cnidarians have radial symmetry, and all
animals with this symmetry lack a head.
 Definition: body plan in which an organism can be
divided into equal parts around a central axis
 Fluid in the body cavity provides body support and
helps give cnidarians their shape.

MOVEMENT: Most cnidarians are slow-moving or sessile
and can be found on shallow ocean floors or on the bottom of
ponds.


All cnidarians have specialized stinging cells used
for defense and capturing prey called cnidocytes 
they are abundant along the tentacles and a stinging
capsule is located within each cnidocyte.
 Definition: specialized cell in cnidarians that functions in
defense and capturing prey
The tentacles of a hydra are armed with numerous
cnidocytes and each cnidocyte holds a stinging
capsule called a nematocyst  when triggered by
touch, the fine, coiled tubule within the nematocyst
shoots out toward the prey.
 Definition: stinging capsule found in a cnidocyte
 Each nematocyst can fire only once.

DIET: Once a cnidarian captures its prey, its tentacles
maneuver the food into its mouth, located at the center of the
ring of tentacles. The mouth leads to the gastrovascular cavity.
 Definition: digestive sac
 The food that enters the digestive sac is digested at
that location and undigested material is released
back out through the mouth.
 Circulating fluids inside the cavity transport digested
food to the cells lining the cavity.

DIFFERENCES: Cnidarians have features that are absent in
sponges but present in nearly all other animals.
 Cnidarians have the presence of a gastrula stage during
embryonic development.
 Cnidarians have an outer covering (epidermis) that has
protective and sensing functions.
 The nerves enable the hydra to respond to stimuli and
coordinate its movements.
Diversity of Cnidarians


There are about 9,000 known species of cnidarians.
These organisms have two kinds of body forms –
either the polyp or the medusa.
Definition: cnidarian body form consisting of a
cylindrical body with tentacles radiating from one end
 Definition: cnidarian body form that is umbrella-shaped
with fringes of tentacles


POLYP: mostly sessile organisms (hydra)

MEDUSA: move freely about in the water (jellyfish)