Marine Animals Without a Backbone
Part 1: Intro, Porifera,
Cnidarians,Ctenophores
Marine Biology - Ch. 7
What is an Animal?
• Multicellular organism
• Heterotroph
– Cannot manufacture its
own food
Vertebrate vs. Invertebrate
• A vertebrate is an animal with a backbone
– A row of bones called vertebrae
• An invertebrate is an animal
without a backbone
– 97% of all animal species
– Most all invertebrates are marine
• Major exception: insects
Phylum Poriphera = “pore bearers”
• Sponges
• Aggregations of specialized cells
• Cellular level of organization
– No true tissues
– No organs
• Nearly all marine
• Sessile
Feeding in Poriphera
• Ostia: numerous tiny pores on the surface
– Allow water to enter and circulate
– Filter plankton and organic particles
Outer surface: pinacocytes and porocytes.
Water is pumped in through pores to larger
feeding chamber lines with choanocytes.
Flagellum creates current. Collar traps food
particles. Water exits through the osculum.
Active vs. passive suspension feeders
• Sponges are suspension feeders
– Eat particles that are suspended in water
• Sponges are filter feeders
– Actively pump or filter food particles.
• Passive suspension feeders
– Don’t actively pump water
– Use cilia and mucus to move food to mouth
Suspension vs. deposit feeders
• Deposit feeders
– Feed on particulate organic matter that settles to
the bottom
– (tube dwelling polychaetes may switch between
passive filter feeding and deposit feeding)
Supporting structures
• Spicules
– Calcareous
– Siliceous
Spongin
-- tough, elastic fibers
-- made of protein
Both are
secreted by
wandering
cells called
amebocytes
Reproduction in Sponges
• Asexual
• Sexual
– Gametes produced
• specialized collar cells or amebocytes develop into
gametes
– No gonads
– Mostly hermaphrodites
– Broadcast spawning
• Gametes released into the water
• Eggs may be retained in the body
encrusting
tubular
Coralline sponge, or sclerosponge
Cnidarians
• Phylum Cnidaria
• Also known as coelenterates
• Includes:
– Sea anemones
– Jellyfish
– corals
More complex than sponges
• Tissues to perform specific functions
• Radial symmetry
Symmetry
Fig. 7.6
2 basic cnidarian forms
• Medusa
– Bell-like
– Adapted for swimming
• Polyp
– Sac-like attached stage
– Mouth and tentacles oriented upward
Life Cycle
• The planula is the larvae stage
– Cylindrical, ciliated
– Two cell layers
Two-cell layer body
• Exodermis is external
• Gastrodermis in internal
• Narrow, gelatinous middle layer: mesoglea
– Thickened to form bell in jellyfish
Types of Cnidarians
• Hydrozoans (class Hydrozoa)
– Feathery or bushy colonies of tiny polyps
• Scyphozoans(class Scyphozoa)
• Anthozoans (class Anthozoa)
Hydrozoan life cycle: minute medusae
release gametes
Siphonophores – hydrozoans that form
drifting colonies of polyps
Toxins from nematocysts produce painful
reactions in swimmers and divers.
Scyphozoans
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•
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Larger medusae
Small polyp stage
Bell may reach 3m across
Swim with rhythmic contractions of the bell
Carried by currents
Painful stings
Anthozoans
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Solitary or colonial polyps
Lack a medusa stage
Partitioned gut (septa)
Sea anemones, corals
– Gorgonians: colonial, tough, branching skeleton
(seafans)
Feeding and Digestions
• Cnidarians are carnivores
• Nematocysts
– Fluid-filled capsule contains a thread that can be
ejected
– Thread is sticky or spined, wraps around prey
• Food is digested in the gut
• Extracellular and intracellular digestion
Behavior in Cnidarians
• Lack a brain or true nerves
• Have nerve cells
• Nerve cells interconnect to form nerve net
– Allows species identification
– Primitive eyes
• Statocysts in the medusae give a sense of
balance
Ctenophora
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Comb jellies, or ctenophores
Radial symmetry
Gelatinous body
Eight row of ciliary combs
– Beat in waves
– Refract light
• Up to 2 meters long
• Two long-armed tentacles
lined with colloblasts (sticky
cells)