Sponges and Cnidarians
Biology II: Chapter 26
The Animal Kingdom
• Multicellular
• Eukaryotic
• Heterotrophs
• Cells lack cell walls
• 95% are invertebrates
What Animals Do to Survive
• Feeding
• Response
• Respiration
• Movement
• Circulation
• Reproduction
• Excretion
Trends in Animal Evolution
• Cell specialization and levels of organization
• Early development
• Body symmetry
• Cephalization
• Body cavity formation
SPONGES
Sponges
• Phylum Porifera
• Have tiny openings, or pores,
over their bodies
• Sessile: they live their entire life
attached to a single spot
• They are animals! Why…?
all
Sponges are Animals!!!
• Multicellular
• Heterotrophic
• No cell walls
• Contain a few
specialized cells
Form and Function in Sponges
• Have nothing resembling a
mouth or gut
• Have no tissues or organ
systems
• Simple functions are carried
out by a few specialized cells
Asymmetrical
• Have no front or back ends,
no left and right sides
• A large, cylindrical water
pump
• The body forms a wall
around a large central cavity
through which water flows
continually
Choanocytes
• Specialized cells that
use flagella to move a
steady current of water
through the sponge
• Filters several thousand
liters/day
Osculum
• A large hole at the top of
the sponge, through which
water exits
• The movement of water
provides a simple
mechanism for feeding,
respiration, circulation and
excretion
Simple Skeleton
• Spicule: a spike-shaped
structure made of
chalk-like calcium
carbonate or glasslike
silica in hard sponges
• Archaeocytes:
specialized cells that
make spicules
Feeding
• Filter feeders
• Sift microscopic
food from the water
• Particles are engulfed by
choanocytes that line the body cavity
Respiration, Circulation, & Excretion
• Rely on the movement of water through their bodies
to carry out body functions
• As water moves through the cavity:
• Oxygen dissolved in the water diffuses into the
surrounding cells
• Carbon dioxide and other wastes, diffuse into the
water and are carried away
Response
• No nervous system
• Many sponges protect
themselves by producing
toxins that make them
unpalatable or poisonous
to potential predators
Reproduction
• Sexually or asexually
• A single spore forms
both eggs and sperm;
usually at different
times
Sexual Reproduction
• Internal fertilization:
Eggs are fertilized inside
the sponge’s body
• Sperm are released from
one sponge and carried
by currents to the pores
of another sponge
Asexual Reproduction
• Budding
• Gemmules: groups of
archaeocytes surrounded
by spicules
Ecology of Sponges
• Ideal habitats for marine animals such as snails,
sea stars, sea cucumbers, and shrimp
• Mutually beneficial relationships with bacteria,
algae and plant-like protists
– Many are green due to these organisms living in
their tissues
Ecology of Sponges
• Attached to the seafloor and may receive
little sunlight
• Some have spicules that look like crossshaped antennae
• Like a lens or magnifying glass, they focus
and direct incoming sunlight
CNIDARIANS
Cnidarians
• Phylum Cnidaria
• Hydras, jellies,
sea anemones, and corals
• Soft-bodied
• Carnivorous
• Stinging tentacles arranged in circles around their mouths
• Simplest animals to have body symmetry and specialized cells
Cnidocytes
• Stinging cells that
are located on their
tentacles
• Used for defense
and to capture prey
Nematocyst
• A poison-filled, stinging
structure that contains a
tightly coiled dart
• Found within cnidocytes
Form and Function in Cnidarians
• Only a few cells thick
• Simple body systems
• Most of their responses to the environment
are carried out by specialized cells and
tissues
Radially Symmetrical
• Central mouth
surrounded by
numerous tentacles
that extend outward
from the body
• Life cycles includes
a polyp and a
medusa stage
Body Plan
• Polyp: cylindrical
body with arm-like
tentacles; mouth
points upward
• Medusa: motile, bellshaped body; mouth
on the bottom
Feeding
• Polyps and medusas have a body wall that
surrounds an internal space: the
gastrovascular cavity
• Gastrovascular cavity: a digestive chamber
with one opening
– Food enters and wastes leave the body
Respiration, Circulation, & Excretion
• Following digestion, nutrients are usually
transported throughout the body by
diffusion
• Respire and
eliminate wastes
by diffusion
through body walls
Response
• Specialized sensory cells are used to gather
information from the environment
• Nerve net: loosely organized network of nerve cells
that together allow cnidarians to detect stimuli
– Distributed uniformly throughout the body in most species
– In some species it is concentrated around the mouth or in
rings around the body
Response
• Statocysts: groups of
sensory cells that help
determine the direction
of gravity
• Ocelli: eyespots made
of cells that detect light
Movement
• Hydrostatic skeleton: a layer of circular
muscles and a layer of longitudinal muscles
that enable cnidarians to move
Reproduction: Sexually and Asexually
• Polyps can reproduce asexually by budding
• External sexual reproduction
– The sexes are separate-each individual is either
male or female
– Both egg and sperm are released into the water
Groups of Cnidarians
• Jellies (formerly jellyfishes)
• Hydras and their relatives
• Sea anemones
• Corals
Ecology of Corals
• The worldwide distribution is determined by:
– Temperature
– Water depth
– Light intensity
• Many suffer from human activity
• Coral bleaching has become common
• Global warming may add to the problem