Chapter 8
“Lower” Invertebrates: Sponges, Jellies,
Flatworms, Ribbon Worms, Lophophorates
Karleskint
Turner
Small
What Are Animals?
Animals:
1.
2.
3.
4.
multicellular
eukaryotic cells without cell walls
cannot produce their own food (heterotrophic)
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 form most efficient, most common
Sponge Structure and Function
• Nutrition and digestion
– suspension/filter feeders
– collar cells (choanocytes) filter out tiny food
particles
– pinacocytes 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
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 (moss animals)
• Predator-prey relationships
– few species eat sponges, e.g. hawksbill sea turtle
• 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
Polyp & medusa
Stinging Cells
• Cnidocytes
– Nematocysts
Stinging Cells
• Dangerous species
– Portuguese man-of-war
– box jellyfish
Types of Cnidarians
• 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
• “True” Jellyfish
– plankton
– medusa is predominant
– photoreceptors
Types of Cnidarians
• Box jellyfish
– box-shaped bells
– relatively strong
swimmers
– tropical
– complex eyes (imageforming?)
– voracious predators,
primarily of fish
Types of Cnidarians
• Sea anemones
– benthic
– though sessile, many
can change locations
Types of Cnidarians
• Coral animals
– polyps secrete a calcium
carbonate skeleton
– stony corals form reefs
– soft corals
Nick Hobgood
• polyps form plant-like
colonies
Nutrition and Digestion
• Gastro-vascular 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 (zooxanthellae)
Reproduction
• asexual polyp stage
– fission, budding common in corals
– pedal laceration (sea anemones)
– strobilation common in hydroids and jellyfish
• sexual medusa stage
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 with adhesive cells or
incorporated nematocysts from jellyfish prey
The Evolution Of Bilateral Symmetry
• Bilateral symmetry
– allowed for streamline body shape
– Cephalization
– Most animal phyla except sponges, jellies,
(adult) echinoderms
Flatworms
•
•
•
•
Have flattened bodies and simple brains
Turbellarian flatworms – free-living
Flukes – parasitic: internal or external
Tapeworms – parasitic: internal
Helicometria sp fluke from cardinal fish digestive tract
Anon. Wiki Commons
Flatworms
• turbellarians are mostly benthic, infaunal,
members of meiofauna
• flukes usually have complex life cycles,
involving intermediate hosts (e.g. mollusks)
and definite hosts (e.g. fish)
• tapeworms live in the host’s digestive tract
Anon. Wiki Commons
Flatworms
• Ecological role of flatworms
– Turbellarians:
• prey for higher-level consumers
– Parasitic flatworms:
• can regulate population size by lowering fitness of
host
Ribbon Worms
• most are benthic
• carnivorous
• capture prey with
retractable proboscis
http://www.cabrillo.edu/~jcarothers
Ribbon Worms
• Ecological role of ribbon worms
– prey organisms for higher consumers
– burrowing in sediment moves nutrients to surface
– abandoned burrows can serve as habitat
Lophophorates
• sessile animals that lack a distinct head
• lophophore
• 3 phyla of lophophorates:
– lophophorate tube worms)
– colonial bryozoans (“moss animals”)
– lamp shells (attached by fleshy stalks)
http://www.projectnoah.org
http://northislandexplorer.com
Ecological Roles of Lophophorates
• Filter feeders
• Food for many invertebrates, especially
molluscs and crustaceans
• Largely responsible for fouling ship bottoms
p211a
p211b