Download Lower Invertebrates

Lower Invertebrates
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.
Key Concepts
• Most marine animals exhibit bilateral
symmetry.
• Turbellarians are free-living flatworms;
flukes and tapeworms are parasitic
flatworms.
• Ribbon worms are marine predators that
somewhat resemble flatworms.
• Phoronids, bryozoans and brachiopods
have a specialized feeding structure called
a lophphore.
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 (with the exception of adult
sponges)
5. invertebrates = animals that lack a vertebral column
(backbone
6. vertebrates – animals with a vertebral column
7. majority of animals in sea are invertebrates
Sponges
• Phylum Porifera
• 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 spongin
– spongin: a protein that forms flexible fibers
Sponge Structure and Function
• Sponge size and body form
– size is limited by water circulation
– asconoid: simplest form; tubular and always
small, found in clusters
– syconoid: sponges that exhibit the first stages
of body-wall folding
– leuconoid: sponges with the highest degree of
folding, which have many chambers lined with
collar cells
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
– large particles are engulfed and digested by
pinocytes and archaeocytes
– collar cells trap ~ 80% of food which consists of
small particles (0.1 to 1.0 micrometers in size)
– sponges are one of the few animals that can
capture such small sized particles
Sponge Structure and Function
• Reproduction in sponges
– asexual reproduction
• budding: a group of cells on the outer surface of the sponge
develops and grows into a tiny new sponge, which drops off
and establishes itself
• fragmentation: production of a new sponge from pieces that are
broken off by physical processes, e.g., waves, storms,
predators
– sexual reproduction
• most sponges are hermaphrodites
• eggs usually develop from archaeocytes and sperm from
modified collar cells
• larval stage is called a planktonic amphiblastula
Fertilization
Sperm cell
engulfed by a
collar cell
Egg cell
Embryo
Sperm cell
(modified collar cell)
Asexual
reproduction
Bud
Sexual
reproduction
Planktonic
amphiblastula
larva
New sponge
New sponge
Larva settles and
attaches to bottom
or other surface
Stepped Art
Fig. 8-3, p. 195
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
Ecological Roles of Sponges
• Sponges and nutrient cycling
– boring sponges (family Clionidae) recycle
calcium as they burrow into coral and mollusc
shells
Cnidarians: Animals with Stinging Cells
• Phylum Cnidaria
• 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
• Cnida: stinging organelle within a
cnidocyte, which may function in
locomotion, prey capture, or defense
– nematocysts: spearing type cnida, which are
discharged when the cnidocill—a bristle-like
trigger—contacts another object
Stinging Cells
• Stinging cells also triggered by certain
chemical substances released by prey
• Dangerous species
– Portuguese man-of-war (painful stings)
– box jellyfish (can kill within 3-20 minutes)
Types of Cnidarians
• Hydrozoans (class Hydrozoa)
– mostly colonial
– colonial forms contain 2 types of polyp:
• gastrozooid = feeding polyp—functions in food
capture
• gonangium = reproductive polyp—specialized for
reproduction
– 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
Reproduction
• Hydrozoans
– generally exhibit asexual polyp stage and
sexual medusa stage in the life cycle
– reproductive polyps form medusa-like buds
which grow into adults after release
– adults release gametes into the water column,
where they are fertilized and form larvae
• planula larva: planktonic larva disperses and
grows in the water column, then settles
Medusae
Sperm
Egg
Planula larva
Polyp colony
Young polyp colony
Stepped Art
Fig. 8-15, p. 204
Reproduction
• Scyphozoans
– in adult jellyfish and box jellyfish, sexes
generally separate
– medusae (sexual stage) release gametes into
the water column for fertilization
– planula larvae settle, grow into polyps, and
reproduce medusa-like buds asexually
– immature buds are released into the water
column to grow into mature medusae
Young medusa
Adult medusa
Gastrovascular
cavity
Gonad
Bell
Asexual reproduction
Tentacles
Radial canal
Mouth
Oral arms
Egg
Sexual reproduction
Young polyp
Planula
Stepped Art
Fig. 8-16, p. 205
Reproduction
• Anthozoans
– asexual reproduction IS COMMON
• pedal laceration: leaving parts of the pedal disk
(base) behind to grow into new animals
• fission: the anemone splits in two and each half
grows into a new individual
• budding produces large colonies of identical hard
corals asexually
– sexual reproduction
• corals usually have male and female forms, gametes
are released into water column
• larval stage is a 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
• 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
• Algae provide food and oxygen to coral through
photosynthesis
• Coral provides nutrients and carbon dioxide to
algae through respiration
– sea anemones...
• and clownfish
• and the hermit crab
Ctenophores
• 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
• Reproduction
– almost all are hermaphroditic
– fertilization may be in the water column, or
eggs may be brooded in the body
– cydippid larva: free-swimming larva
resembling the adult ctenophore
Ctenophores
• Ecological Role
– can effect zooplankton abundance directly
and fish populations by preying on fish larvae
and eggs
The Evolution Of Bilateral 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)
Flatworms
• Have flattened, bilaterally symmetrical
bodies with a definite head and posterior
end
• Trubellarian flatworms (class Turbellaria)
are free-living
• Flukes (class Trematoda) and tapeworms
(class Cestoda) are parasitic
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
• Reproduction
– can reproduce asexually and regenerate
missing body parts
– sexual reproduction
• reciprocal copulation—when hermaphrodites mate
and fertilize each other
• some have no larval stage; others have freeswimming planktonic larva
• turbellarians produce few eggs
• parasitic flatworms produce 10 to 100 thousand
times more eggs than turbellarians
Flatworms
• Ecological role of flatwroms
– Turbellarians:
• turbellarians funnel nutrients to higher trophic
levels
• prey for higher-level consumers
– Parasitic flatworms:
• can regulate population size by lowering fitness of
host
Ribbon Worms
• Phylum Nemertea
– most are benthic
– resemble flatworms but are longer with thicker
bodies
– sexes are separate, fertilization external
– carnivorous – feed on annelids and
crustaceans
– capture prey with proboscis (tube extending
from mouth)
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
• 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
• Colonies are composed of zooids (tiny individuals),
each inhabiting a box-like chamber it secretes
• 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