Chapter 8
“Lower” Invertebrates I: Sponges & Radiata
Karleskint
Turner
Small
Key Concepts
• Sponges are asymmetric, sessile animals
that filter food from the water circulating
through their bodies.
• Sponges provide habitats for other
animals.
• Cnidarians and ctenophores exhibit radial
symmetry.
• Cnidarians possess a highly specialized
stinging cell used to capture prey and for
protection.
What Are Animals?
Animals:
1.
2.
3.
4.
multicellular
eukaryotic cells without cell walls
cannot produce their own food
Invertebrates or vertebrates
(most animals are invertebrates)
Sponges
Phylum Porifera
• Basic characteristics:
– no tissues or organs
– asymmetric
– sessile
Anon. Wiki Commons
Sponge Structure and Function
Sponge Structure and Function
3 basic body forms: leuconoid from most efficient, most common
Sponge Structure and Function
• Nutrition and digestion
– suspension/filter feeders
– collar cells (choanocytes) filter out tiny food
particles
– pinocytes and archaeocytes (a.k.a. amoebocytes)
ingest larger food particles by phagocytosis
– Most food digested and distributed to other cells
by archaeocytes
Sponge Structure and Function
• Reproduction in sponges
– asexual reproduction
• budding
• fragmentation
– sexual reproduction
• most hermaphrodites
• eggs from archaeocytes and sperm from modified collar cells
Fertilization
Sperm cell
engulfed by a
choanocyte
Egg cell
Asexual
reproduction
Bud
Sperm cell
(modified
choanocyte)
Embryo
Sexual
Planktonic
reproduction amphiblastula
larva
New sponge
New sponge
Larva settles and
attaches to bottom
or other surface
Figure 8-4 p193
Ecological Roles of Sponges
• Competition
– corals and bryozoans
• Predator-prey relationships
– few species eat sponges
• spicules
• chemical deterrents
Ecological Roles of Sponges
• Symbiotic relationships
– mutualistic or commensalistic hosts
– organisms live within the canals
Ecological Roles of Sponges
• Sponges and nutrient cycling
– boring sponges
Cnidarians: Animals with Stinging Cells
• Include jellyfish,
hydroids, corals
and sea
anemones
• cnidocytes
ErgoSum88
Organization of the Cnidarian Body
Stinging Cells
• Cnida
– nematocysts
Stinging Cells
• Dangerous species
– Portuguese man-of-war
– box jellyfish
Types of Cnidarians
• Hydrozoans or Hydroids
– mostly colonial
– colonial forms contain
2 types of polyp:
• Feeding polyp
• Reproductive polyp
– hydrocorals secrete a
calcareous skeleton
– some produce floating
colonies
(e.g. P. man-o-war)
Types of Cnidarians
• Jellyfish
– scyphozoans—true jellyfish (class Scyphozoa)
• plankton
• medusa is predominant
• photoreceptors
Types of Cnidarians
• Box jellyfish
– box jellyfish (class
Cubozoa)
•
•
•
•
box-shaped bells
relatively strong swimmers
tropical
complex eyes (imageforming?)
• voracious predators,
primarily of fish
Types of Cnidarians
• Anthozoans (class
Anthozoa)
– include sea anemones,
corals and gorgonians
– sea anemones
• benthic
• gastrovascular cavity
divided
• though sessile, many can
change locations
Types of Cnidarians
• Anthozoans (class
Anthozoa)
– coral animals
• polyps secrete a
calcium carbonate
skeleton
• stony corals form reefs
Nick Hobgood
Types of Cnidarians
• Anthozoans (class Anthozoa)
– soft corals
• polyps that form plant-like colonies
Nutrition and Digestion
• Gastrovascular cavity
– digestion and transport
– 1 opening: mouth/anus
• Many suspension feeders
• Jellyfish and box jellyfish are carnivorous
• Sea anemones generally feed on invertebrates,
some large species feed on fish, shallow water
species have symbiotic algae
Reproduction
• asexual polyp stage
– fission, budding common in corals
– strobilation common in hydroids and jellyfish
• sexual medusa stage
Reproduction
• Anthozoans
– asexual reproduction IS COMMON
• pedal laceration
• fission
• budding
– sexual reproduction
• male and female forms, gametes are released
• planula larva
Ecological Relationships of Cnidarians
• Predator-prey
relationships
– cnidarians are predators
– stinging cells discourage
predation
– sea turtles, some fish
and molluscs prey on
hydrozoans and jellyfish
Ecological Relationships of Cnidarians
• Habitat formation
– coral polyps form
complex 3-dimensional
structures inhabited by
thousands of other
organisms
– coral reefs provide a
solid surface for
attachment, places for
pelagic animals to rest
and hide and buffer
waves and storms
Terry Hughes
Ecological Relationships of Cnidarians
• Symbiotic relationships
– Portuguese man-of-war and man-of-war fish
– reef-forming corals and zooxanthellae
– sea anemones:
• clownfish
• hermit crab
Ctenophores
• Planktonic, nearly transparent
• Ctenophore structure
– 8 rows of comb plates
– radial symmetry
– lack stinging cells
– bioluminescent
Ctenophores
• Digestion and nutrition
– Gastro-vascular cavity
– feeds on plankton, larval fish and fish eggs
– branched tentacles, adhesive cells, jellyfish
stingers to capture prey