Download 2006 Thomson-Brooks Cole Chapter 8 Sponges, Cnidarians, Comb

Chapter 8
Sponges, Cnidarians, Comb
Jellies, and Marine Worms
© 2006 Thomson-Brooks Cole
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.
© 2006 Thomson-Brooks Cole
Key Concepts
• Marine worms exhibit bilateral
symmetry.
• Turbellarians are free-living flatworms;
flukes and tapeworms are parasitic
flatworms.
• Nematodes are abundant and
important members of the meiofauna.
• Polychaete diversity stems from the
evolution of a segmented body that
allows increased motility.
© 2006 Thomson-Brooks Cole
Key Concepts
• In addition to being important
consumer organisms, polychaetes are
the primary prey of many marine
animals and play an important role in
recycling nutrients.
• Several other groups of wormlike
animals, including ribbon worms,
spiny-headed worms, peanut worms,
acorn worms, and beardworms, play
important ecological roles in the
marine environment.
© 2006 Thomson-Brooks Cole
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, so they
depend on other organisms for nutrients
4. can actively move (with the exception of
adult sponges)
© 2006 Thomson-Brooks Cole
Sponges
• Phylum Porifera
• Basic characteristics:
– simple
– asymmetric
– sessile—permanently attached to a solid
surface
– have many shapes, sizes and colors
© 2006 Thomson-Brooks Cole
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
– osculum—large opening through which
water exits from the spongocoel
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
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 the body
• can assume any of the other cell forms, or
transport materials
© 2006 Thomson-Brooks Cole
Sponge Structure and
Function
• Structural materials
– spicules—skeletal elements that give
support to a sponge’s body, which are
produced by specialized cells and
composed of calcium carbonate, silica or
spongin
– spongin—a protein that forms flexible
fibers
© 2006 Thomson-Brooks Cole
Sponge Structure and
Function
• Sponge size and body form
– size is limited by water circulation
– asconoid—simplest form; tubular and
always small
– 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
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Sponge Structure and
Function
• Nutrition and digestion
– sponges are suspension feeders – they
feed on material that is suspended in
seawater
– sponges are filter feeders – they filter
their food from the water
– sponges are one of the few animals that
can capture particles 0.1 to 1.0
micrometers in size
© 2006 Thomson-Brooks Cole
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
• fragmentation—production of a new sponge
from pieces that are broken off
– sexual reproduction
• eggs usually develop from archaeocytes and
sperm from modified collar cells
• larval stage is a planktonic amphiblastula
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Ecological Roles of Sponges
• Competition
– compete for space to attach with corals
and bryozoans
• Predator-prey relationships
– few species eat sponges
• spicules are like needles
• some produce chemical deterrents
– major food source for hawksbill sea turtle
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Ecological Roles of Sponges
• Symbiotic relationships
– sponges are mutualistic or commensalistic
hosts to many organisms
• e.g. mutualistic bacteria
– many organisms live within the canals or
spongocoel, for protection, water flow
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Ecological Roles of Sponges
• Sponges and nutrient cycling
– boring sponges recycle calcium as they
burrow into coral and mollusc shells
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Cnidarians: Animals with
Stinging Cells
• Phylum Cnidaria
• Named for their cnidocytes—stinging
cells
• Cnidocytes are used to capture prey
and protect the animal
© 2006 Thomson-Brooks Cole
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—a benthic form characterized by a
cylindrical body with an opening at 1 end
– medusa—a free-floating stage (jellyfish)
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Stinging Cells
• Cnida—stinging organelle within a
cnidocyte, which may function in
locomotion, prey capture, or defense
– nematocysts—spearing type, which are
discharged when the cnidocill—a bristlelike trigger—contacts another object
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Stinging Cells
• Dangerous species
– Portuguese man-of-war (painful stings)
– box jellyfish (can kill within 3-20 minutes)
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Types of Cnidarians
• Hydrozoans (class Hydrozoa)
– mostly colonial
– colonial forms contain 2 types of polyp:
• feeding polyp—functions in food capture
• reproductive polyp—specialized for
reproduction
– hydrocorals secrete a calcareous skeleton
– some produce floating colonies
• e.g. Portuguese man-of-war
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Types of Cnidarians
• Jellyfish and box jellyfish
– scyphozoans—true jellyfish (class
Scyphozoa)
• medusa is predominant life stage
• photoreceptors—sense organs that can
determine whether it is dark or light
– box jellyfish (class Cubozoa)
• tropical
• voracious predators, primarily of fish
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Types of Cnidarians
• Anthozoans (class Anthozoa)
– sea anemones
• polyps with a vascular cavity divided into
compartments radiating from the central one
• though sessile, many can change locations
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Types of Cnidarians
• Anthozoans (class Anthozoa)
– coral animals
• polyps that secrete a hard or soft skeleton
• form reefs along with types of algae
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Types of Cnidarians
• Anthozoans (class Anthozoa)
– soft corals
• polyps that form plant-like colonies
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Nutrition and Digestion
• Gastrovascular cavity—central cavity
where cnidarians digest their prey
– functions in digestion and transport
• Many hydrozoans and anthozoans are
suspension feeders
• Jellyfish and box jellyfish eat fish and
larger invertebrates
• Sea anemones generally feed on
invertebrates
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
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,
where they are fertilized and form larvae
• planula larva—planktonic larva that grows in
the water column, then settles
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Reproduction
• Scyphozoans
– medusae (sexual stage) release gametes
into the water for fertilization
– planula larvae settle, grow into polyps,
and reproduce medusa-like buds asexually
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Reproduction
• Anthozoans
– asexual reproduction
• 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
– sexual reproduction
• larval stage is a planula larva
© 2006 Thomson-Brooks Cole
Ecological Relationships of
Cnidarians
• Predator-prey relationships
– cnidarians are predators
– stinging cells discourage predation
• Habitat formation
– coral polyps form complex 3-dimensional
structures inhabited by thousands of other
organisms
– coral reefs provide a solid surface for
attachment, and buffer waves and storms
© 2006 Thomson-Brooks Cole
Ecological Relationships of
Cnidarians
• Symbiotic relationships
– Portuguese man-of-war and man-of-war
fish
– reef-forming corals and zooxanthellae
– sea anemones...
• and clownfish
• and the hermit crab
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
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
– bioluminescent
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Ctenophores
• Digestion and nutrition
– carnivorous, feeding on other planktonic
animals
– may used branched tentacles in a net
pattern, adhesive cells, jellyfish stingers
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
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
© 2006 Thomson-Brooks Cole
Marine Worms
• Have elongated bodies, most lacking
any kind of external hard covering
• Most exhibit a hydrostatic skeleton—
support is provided by body fluid
• Types of marine worms include:
– flatworms
– nematodes
– annelid worms
– others
© 2006 Thomson-Brooks Cole
Flatworms
• Have flattened bodies with a definite head
and posterior end
• Trubellarian flatworms (class Turbellaria) are
free-living
• Flukes (class Trematoda) and tapeworms
(class Cestoda) are parasitic
• Bilateral symmetry—body parts are arranged
in such a way that only one plane through
the midline of the central axis will divide the
animal into similar right and left halves
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Flatworms
• Bilateral symmetry favors
cephalization—the concentration of
sense organs in the head region
• Types of flatworm
– turbellarians are mostly pelagic, and are
common members of meiofauna
(invertebrates living between sediment
particles)
– flukes usually have complex life cycles
– tapeworms live in the host’s digestive
tract
© 2006 Thomson-Brooks Cole
Flatworms
• Reproduction
– can reproduce asexually and regenerate
missing body parts
– sexual reproduction
• reciprocal copulation—when hermaphrodites
fertilize each other
• some have no larval stage; others have freeswimming planktonic larva
© 2006 Thomson-Brooks Cole
Nematodes
• Phylum Nematoda
• Roundworms – the most numerous
animals on earth
• Important as scavengers or parasites
• Many free-living nematodes are
carnivorous
• Most are hermaphroditic, but some
have separate sexes
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Annelids: The Segmented
Worms
• Annelids—worms whose bodies are divided
internally and externally into segments
– segments increase mobility by enhancing
leverage
– setae—small bristles used for locomotion,
digging, anchorage and protection
• Types of marine annelids
– polychaetes
– echiurans
– pogonophorans
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Polychaetes
• Polychaetes (class Polychaeta) are the
most common marine annelids
• Traditionally divided into 2 groups:
– errant polychaetes (move actively)
• may be strictly pelagic, crawl beneath rocks
and shells, be active burrowers in sand or
mud, or live in tubes
– sedentary polychaetes (sessile)
• e.g. tube worms
• create tubes from a variety of materials
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Polychaetes
• Feeding and digestion
– some errant species are active predators;
tube dwellers may partially or completely
leave the tube to feed
– many sedentary species are filter or
suspension feeders
– digestive tract is usually a straight tube
from the mouth to the posterior anus
• food enters the mouth, nutrients are absorbed
in the intestine, and wastes are excreted
through the anus
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Polychaetes
– deposit feeders—animals that feed on
organic material mixed with mineral
deposits which settle on the sea bottom
• nonselective deposit feeders ingest both
organic and mineral particles, digest the
organic particles, and excrete the minerals
– fecal casts—piles of defecated undigested materials
• selective deposit feeders separate organic
materials from minerals and ingest the former
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Polychaetes
• Reproduction in polychaetes
– asexual reproduction via budding or
fragmentation occurs in some polychaetes
– most reproduce only sexually, with the
majority having separate sexes
– gametes are released into the water
– epitoky—the formation of a pelagic
reproductive individual (epitoke) that is
different from the non-reproductive form
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Polychaetes
– epitoky in polychaetes
• swarming—males and females come to the
surface in large numbers at night to shed
sperm and eggs
• swarming of epitokes occurs only at specific
times of year, and seems related to lunar
cycles and tides
© 2006 Thomson-Brooks Cole
Echiurans
• Spoonworms (class Echiura)
• Sausage-shaped annelids resembling
sipunculid worms
• Mostly deposit feeders; at least 1 is a filter
feeder
– deposit feeders typically have a flat, ribbon-like
proboscis (tube extending from the mouth) to
collect particles
• Have separate sexes, shed gametes into the
water, and have a planktonic larval stage
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Pogonophorans
• Beardworms (class Pogonophora)
• Live in buried tubes and have a
cylindrical body with a ring of tentacles
around the anterior end
• Lack mouth or digestive tract
• May absorb nutrients dissolved in the
water or obtain nourishment from
chemosynthetic bacteria (those living
in vent communities)
© 2006 Thomson-Brooks Cole
Other Marine Worms
• Other worm-like animals live in the sea
• Anatomically and developmentally
different
• Types include:
– ribbon worms
– sipunculids
– priapulids
– hemichordates
– gastrotrichs, nematomorphs,
acanthocephalans
© 2006 Thomson-Brooks Cole
Ribbon Worms
• Phylum Nemertea
• Have ribbon-like bodies; similar to
flatworms, but longer and thicker
• Mostly benthic (some deepwater
species are pelagic)
• Some reproduce asexually by
fragmentation; most have separate
sexes and external fertilization
• Carnivorous, catching prey (annelids,
crustaceans) with a proboscis
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Sipunculids
• Phylum Sipuncula
• Solitary benthic worms that live in burrows
in mud or sand, empty mollusc shells, or
coral crevices
• Some known as peanut worms – they
contract into a peanut shape when disturbed
• Either suspension or deposit feeders; have a
proboscis and ring of tentacles
• Separate sexes, external fertilization; may
either develop directly into worms or have a
larval stage
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Priapulids
• Benthic worms that bury themselves in
sand and mud in shallow or deep water
• Small species belong to meiofauna;
may be deposit or suspension feeders
• Larger species are thought to be
carnivorous
• Have separate sexes; fertilization is
external in large species but probably
internal in smaller ones; larvae inhabit
benthic mud
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Hemichordates
• Acorn worms (phylum Hemichordata)
• Sessile bottom dwellers that burrow in
sediments of intertidal mud or sand
flats or under stones
• Collects food with a large proboscis
• Some species use their proboscis to
dig burrows; the head protrudes from
one end of the burrow, while the anus
deposits fecal material near the other
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Gastrotrichs, Nematomorphs,
and Acanthocephalans
• Gastrotrics (phylum Gastrotricha)
– small worms inhabiting spaces between
sediment particles, surface of detritus,
and surfaces of submerged plants/animals
• Neatomorphs, or horsehair worms
(phylum Nematomorpha)
– name derived from resemblance to the
hairs of a horse’s tail
– free-living as adults
– parasites of arthropods as juveniles
© 2006 Thomson-Brooks Cole
Gastrotrichs, Nematomorphs,
and Acanthocephalans
• Acanthocephalans, or spiny-headed
worms (phylum Acanthocephala)
– parasites, mostly of fish, birds and
mammals
– name is derived from cylindrical proboscis
with several rows of spines, which is used
to penetrate the intestine of the host
© 2006 Thomson-Brooks Cole
Ecological Roles of Marine
Worms
• Nutrient cycling
– as burrowing organisms, they release
nutrient buried in the ocean bottom back
to the surface for use by producers
• Predator-prey relationships
– important links in food chains – consume
organic matter unavailable to larger
consumers, and then become food for
larger consumers themselves
© 2006 Thomson-Brooks Cole
Ecological Roles of Marine
Worms
– nematodes are the most abundant
members of meiofauna
– echiurans may be significant in the diet of
some fishes
– polychaetes are a major food source for
invertebrates and vertebrates
• Symbiotic relationships
– non-carnivorous tube-dwelling and
burrowing polychaetes provide a retreat
for commensal organisms
© 2006 Thomson-Brooks Cole
Ecological Roles of Marine
Worms
• Population dynamics
– populations may be limited by physical or
biological factors
– infaunal polychaetes do not appear to be
limited by resources, but by predation
• size of the polychaete population increased 2
or 3 times when areas in the York River
estuary of the Chesapeake Bay were protected
form predatory fish and crabs by wire cages
© 2006 Thomson-Brooks Cole