Unit 8 Invertebrates
Ch. 26 Sponges & Cnidarians
Introduction to the Animal
Kingdom
Animals, members of the kingdom
Animalia, are multicellular, eukaryotic
heterotrophs whose cells lack cell walls
What Is an Animal?
Invertebrates - animals that do not have a
backbone, or vertebral column
Vertebrates - animals with a backbone
What Animals Do to Survive
Animals carry out the following essential
functions: feeding, respiration,
circulation, excretion, response,
movement, & reproduction
What Animals Do to Survive
Feeding
Most animals cannot absorb food, instead,
they ingest (or eat) it
What Animals Do to Survive
Respiration
Whether they live in water or on land, all
animals respire, they take in oxygen & give
off carbon dioxide
What Animals Do to Survive
Circulation
Small animals rely on diffusion to transport
nutrients
Large animals have a circulatory system to
move nutrients around
What Animals Do to Survive
Excretion
Most animals have an excretory system that
eliminates wastes, maintaining homeostasis
What Animals Do to Survive
Response
Animals respond to events in their
environment using specialized cells called
nerve cells
What Animals Do to Survive
Movement
Most animals are motile, meaning they can
move around
What Animals Do to Survive
Reproduction
Most animals reproduce sexually, which
helps create & maintain genetic diversity in
populations
It improves the species ability to evolve when
the environment changes
Trends in Animal Evolution
Complex animals tend to have high levels
of cell specialization & internal body
organization, bilateral body symmetry, a
front end or head with sense organs, & a
body cavity
Trends in Animal Evolution
Trends in Animal Evolution
Body symmetry
Radial symmetry - similar to a bicycle wheel,
any number of imaginary planes can be
drawn through the center
Bilateral symmetry - a single imaginary
plane can divide the body into 2 equal sides
Body Symmetry
Trends in Animal Evolution
Cephalization - the concentration of
sense organs & nerve cells at the front
end of the body
What Is a Sponge?
Sponges are classified as animals
because they are multicellular,
heterotrophic, have no cell walls, &
contain a few specialized cells
Form & Function in Sponges
The movement of water through the
sponge provides a simple mechanism for
feeding, respiration, circulation, &
excretion
Ecology of Sponges
Sponges often provide habitats for other
organisms
What Is a Cnidarian?
Cnidarians are soft-bodied, carnivorous
animals that have stinging tentacles
arranged in circles around their mouths
They are the simplest
animals to have body
symmetry &
specialized tissues
Form & Function in Cnidarians
Cnidarians typically have a life-cycle that
includes 2 different-looking stages: a
polyp & a medusa
Form & Function in Cnidarians
Response
Many cnidarians respond to touch by pulling
their tentacles inside their bodies
Form & Function in Cnidarians
Movement
Jellyfishes move by means of jet propulsion
The body contracts to force water out,
moving the jellyfish in the opposite direction
Groups of Cnidarians
Cnidarians include jellyfishes, hydras &
their relatives, & sea anemones & corals
Groups of Cnidarians
Like many marine organisms, jellyfishes
use bioluminescence, or the production of
light by an organism, to ward off
predators
The entire body becomes bioluminescent
when threatened
Groups of Cnidarians
Hydras live solely as polyps
Ex.) Portuguese man-of-war
Groups of Cnidarians
Sea anemones are polyps that live at all
depths of the ocean
Coral reefs are home to many types of
organisms & are as diverse as rain
forests
Ecology of Corals
In normal conditions, algae live within
coral tissues, carrying out photosynthesis
& giving the coral its green appearance
When stressed by pollutants or increasing
temps., these algae can die, so only the
clear cells of the coral remain