Who, What, When, Where, Why, and How of
Lower Invertebrates
•
•
•
•
•
Who studies invertebrates?
What are invertebrates?
When did bilateral symmetry evolve?
Where are invertebrates found?
Why are invertebrates important to the
Marine Ecosystem?
• How do marine invertebrates influence the
marine ecosystem?
Chapter 8
Lower Invertebrates
Karleskint
Turner
Small
What Are Animals?
•
Animals:
1. are multicellular
–
distinguishes them from bacteria and most protists
2. have eukaryotic cells without cell walls
–
distinguishes them from bacteria, fungi, algae and plants
3. cannot produce their own food, depend on other
organisms for nutrients
4. can actively move at least at some point during their
life cycle
5. invertebrates = animals that lack a vertebral column
(backbone
6. vertebrates – animals with a vertebral column
7. majority of animals in sea are invertebrates
• The first animals we will talk about are
sponges
• They are assymetrical – no symmetry
• No true tisses
Phylum Porifera: Sponges
• Basic characteristics:
– simple
– asymmetric
– sessile: permanently attached to a solid surface
– have many shapes, sizes and colors
– shape often determined by shape of bottom
sediments, material on which they are growing
and local water currents
Sponge Structure and Function
• Body is built around a system of water
canals
– ostia: tiny holes or pores through which water
enters the sponge’s body
– spongocoel: spacious cavity in the sponge
into which water flows
– osculum: large opening through which water
exits from the spongocoel
Water exits
through osculum
Spicule
Archaeocyte
Water
enters
through
small
pores
(ostia)
Pinacocyte
Spongocoel
Pore cells
Spongocoel
Collar
cell
(choanocyte)
Collar
Ostium
Flagellum
Food particles
Stepped Art
Fig. 8-1, p. 193
Sponge Structure and Function
• Lacking tissues, sponges have specialized
cells
– collar cells (choanocytes) use their flagella to
provide force for moving water through the
sponge’s body
– pinacocytes in a layer provide an outer covering
for the sponge
– archaeocytes: cells that resemble amoebas,
and can move through sponge body
• can assume any of the other cell forms
• transport materials
• important role in repair and regeneration
Sponge Structure and Function
• Structural materials
– spicules: skeletal elements that give support
to a sponge’s body, produced by specialized
cells and composed of calcium carbonate,
silica or sponging
• Helps also with protection – will keep other animals
from eating the sponges
Sponge Structure and Function
• Nutrition and digestion
– sponges are suspension feeders – feed on
material suspended in seawater
– sponges are also referred to as filter feeders –
they filter food from the water
Ecological Roles of Sponges
• Competition
– compete aggressively with corals and
bryozoans for attachment space
• Predator-prey relationships
– few species eat sponges
• spicules are like needles
• some produce chemical deterrents
– a few species of bony fish and molluscs and
sea turtles (especially the hawksbill) will eat
sponges
Ecological Roles of Sponges
• Symbiotic relationships
– sponges are mutualistic or commensalistic
hosts to many organisms
• e.g. symbiotic cyanobacteria
– many organisms (shrimp, fish) live within the
canals or spongocoel, for protection and to
take advantage of water flow
• Now we will talk about animals with radial
symmetry
Phylum Cnidaria
• Animals with stinging cells
• Include jellyfish, hydroids, corals and sea
anemones
• Named for their cnidocytes—stinging cells
• Cnidocytes are used to capture prey and
protect the animal
Organization of the Cnidarian Body
• Radial symmetry: many planes can be drawn
through the central axis that will divide the
animal into equivalent halves
• Often exhibit 2 body plans within their life cycles:
– polyp: benthic form characterized by a cylindrical
body with an opening at 1 end, i.e., the mouth which
is surrounded by tentacles
– medusa: a free-floating stage (jellyfish)
• Many cnidarians have both body plans, corals
and sea anemones exist as polyps
Stinging Cells
• Cnidocytes have nematocysts
– nematocysts: discharged when it contacts
another object
Stinging Cells
• Why do they need stinging cells?
• They have very flimsy body plan. They must
paralyze their prey (sometimes a large fish), so
that they can digest it
• Dangerous species
– Portuguese man-of-war (painful stings)
– box jellyfish (can kill within 3-20 minutes)
• Groups of cnidarians
– hydrozoans
– Anthozoans
– Scyphozoans
– cubozoans
Types of Cnidarians
• Hydrozoans (class Hydrozoa)
– mostly colonial
– hydrozoans known as hydrocorals secrete a
calcareous skeleton, e.g., fire coral
– some produce floating colonies
• e.g. Portuguese man-of-war
Types of Cnidarians
• Jellyfish and box jellyfish
– scyphozoans—true jellyfish (class Scyphozoa)
• considered members of the plankton
• medusa is predominant life stage
• photoreceptors: sense organs that can determine
whether it is dark or light
– box jellyfish (class Cubozoa)
•
•
•
•
box-shaped bells
relatively strong swimmers
tropical
voracious predators, primarily of fish
Types of Cnidarians
• Anthozoans (class Anthozoa)
– include sea anemones, corals and gorgonians
– Sea anemones
• benthic, all adults are sessile
• polyps with a gastrovascular cavity divided into
compartments radiating from the central one
• though sessile, many can change locations
Types of Cnidarians
• Anthozoans (class Anthozoa)
– Coral animals
• polyps that secrete a hard or soft skeleton
• scleractinian corals = hard, stony corals
• form reefs along with coralline red algae and
calcified green algae
Types of Cnidarians
• Anthozoans (class Anthozoa)
– soft corals
• polyps that form plant-like colonies
Nutrition and Digestion
• Gastrovascular cavity: central cavity where
cnidarians digest their prey
– functions in digestion and transport
– waste products forced back out mouth
• Many hydrozoans and anthozoans are suspension
feeders
• Jellyfish and box jellyfish are carnivorous, eat fish
and larger invertebrates
• Sea anemones generally feed on invertebrates,
some large species feed on fish, shallow water
species have symbiotic algae
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
• 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
Ecological Relationships of Cnidarians
• Symbiotic relationships
– Portuguese man-of-war and man-of-war fish
– reef-forming corals and zooxanthellae
• The zooxanthellae (dinoflagellate algal protist)
provide food and oxygen to coral through
photosynthesis
• Coral provides nutrients and carbon dioxide to
algae through respiration
– sea anemones...
• Have symbiotic relationship with the clownfish
• and the hermit crab
Phylum Ctenophora
• Phylum Ctenophora
• Planktonic, nearly transparent
• Ctenophore structure
– named for 8 rows of comb plates (ctenes)
which the animal uses for locomotion
• ctenes are composed of large cilia
– exhibit radial symmetry
– lack stinging cells
– bioluminescent
Ctenophores
• Digestion and nutrition
– carnivorous, feeding on other plankton, larval
fish and fish eggs
– may use branched tentacles in a net pattern,
adhesive cells, jellyfish stingers to capture
prey
Ctenophores
• Ecological Role
– can effect zooplankton abundance directly
and fish populations by preying on fish larvae
and eggs
• Now we will talk about animals with
bilateral symmetry – all other animals have
this type of symmetry
– Bilateral symmetry
• body parts arranged such that only one plane
through the mid-line of the central axis divides
animal into similar right and left halves
• allowed for streamline body shape increasing
mobility
• favored concentration of sense organs at one end
of animal (cephalization)
Phylum Platyhelminthes
• Flatworms
– Have flattened, bilaterally symmetrical bodies
with a definite head and posterior end
– 3 groups
• Turbellaria – free living
• Trematoda – parasitic flukes
• Cestoda – parasitic tapeworms
Flatworms
• Types of flatworm
– turbellarians are mostly pelagic, and are
common members of meiofauna (invertebrates
living between sediment particles)
– turbellarians have sensory receptors in head
region to detect light, chemicals, movement and
help maintain balance
– flukes usually have complex life cycles
– tapeworms live in the host’s digestive tract
Flatworms
• Ecological role of flatworms
– Turbellarians:
• turbellarians funnel nutrients to higher trophic
levels
• prey for higher-level consumers
– Parasitic flatworms:
• can regulate population size by lowering fitness of
host
Lophophorates
• Lophophorates are sessile animals that
lack a distinct head
• Possess a lophophore: arrangement of
ciliated tentacles that surround the mouth,
used for feeding, gas exchange
• 3 phyla of lophophorates:
– Phoronida (phoronids)
– Ectoprocta (bryozoans)
– Brachiopoda (brachiopods)
Phoronids
• Small, worm-like animals
• Secrete a tube of leathery protein or chitin
that can be attached or buried in bottom
sediments
• Catch plankton and detritus with mucuscoated tentacles
• Can reproduce sexually or asexually
(budding, transverse fission)
• Have a planktonic larval stage
Bryozoans
• Small, abundant, colonial animals
• Most live on rocks, shell, algae, mangroves, etc. in
shallow water
• Along with hydroids, rank among the most
abundant marine epiphytic animals
• Most are hermaphroditic brooders
• Larvae are planktonic, settle to form new colonies
Brachiopods
• Most brachiopods (lamp shells) are benthic and
live in shallow water
• changed little since they evolved 400 million years
ago
• Have mollusc-like, bivalve shells
– valves differ in size and shape, and are dorsal and
ventral
– a pedicle (fleshy stalk) attaches the shell or is buried
• Gather detritus/algae with lophophore
• Generally have separate sexes; larvae are
planktonic and settle in 24-30 hrs.
Ecological Roles of Lophophorates
• As a group, they are filter feeders
• Food for many invertebrates, especially
molluscs and crustaceans
• Largely responsible for fouling ship
bottoms