Sponges and Cnidarians
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Transcript of Sponges and Cnidarians
The Animal Kingdom
• Multicellular
• Eukaryotic
• Heterotrophs
• Cells lack cell walls
• 95% are invertebrates
What Animals Do to Survive
• Feeding
• Respiration
• Circulation
• Excretion
• Response
• Movement
• Reproduction
Trends in Animal Evolution
• Cell specialization and levels of organization
• Early development
• Body symmetry
• Cephalization
• Body cavity formation
Sponges• Phylum Porifera
• Have tiny openings, or pores, all over their bodies
• Sessile: they live their entire life attached to a single spot
• They are animals! Why…?
Sponges are Animals!!!
• Multicellular
• Heterotrophic
• No cell walls
• Contain a few specialized cells
Form and Function in Sponges
• Have nothing resembling a mouth or gut
• Have no tissues or organ systems
• Simple functions are carried out by a few specialized cells
Asymmetrical
• Have no front or back ends, no left and right sides
• A large, cylindrical water pump
• The body forms a wall around a large central cavity through which water flows continually
Choanocytes
• Specialized cells that use flagella to move a steady current of water through the sponge
• Filters several thousand liters/day
Osculum
• A large hole at the top of the sponge, through which water exits
• The movement of water provides a simple mechanism for feeding, respiration, circulation and excretion
Simple Skeleton
• Spicule: a spike-shaped structure made of chalk-like calcium carbonate or glasslike silica in hard sponges
• Archaeocytes: specialized cells that make spicules
Feeding
• Filter feeders
• Sift microscopic food from the water
• Particles are engulfed by choanocytes that line the body cavity
Respiration, Circulation, & Excretion
• Rely on the movement of water through their bodies to carry out body functions
• As water moves through the cavity:
• Oxygen dissolved in the water diffuses into the surrounding cells
• Carbon dioxide and other wastes, diffuse into the water and are carried away
Response
• No nervous system
• Many sponges protect themselves by producing toxins that make them unpalatable or poisonous to potential predators
Reproduction
• Sexually or asexually
• A single spore forms both eggs and sperm; usually at different times
Sexual Reproduction
• Internal fertilization: Eggs are fertilized inside the sponge’s body
• Sperm are released from one sponge and carried by currents to the pores of another sponge
Ecology of Sponges
• Ideal habitats for marine animals such as snails, sea stars, sea cucumbers, and shrimp
• Mutually beneficial relationships with bacteria, algae and plant-like protists
– Many are green due to these organisms living in their tissues
Ecology of Sponges
• Attached to the seafloor and may receive little sunlight
• Some have spicules that look like cross-shaped antennae
• Like a lens or magnifying glass, they focus and direct incoming sunlight
Cnidarians• Phylum Cnidaria
• Hydras, jellies, sea anemones, and corals
• Soft-bodied
• Carnivorous
• Stinging tentacles arranged in circles around their mouths
• Simplest animals to have body symmetry and specialized cells
Cnidocytes
• Stinging cells that are located on their tentacles
• Used for defense and to capture prey
Nematocyst
• A poison-filled, stinging structure that contains a tightly coiled dart
• Found within cnidocytes
Form and Function in Cnidarians
• Only a few cells thick
• Simple body systems
• Most of their responses to the environment are carried out by specialized cells and tissues
Radially Symmetrical
• Central mouth surrounded by numerous tentacles that extend outward from the body
• Life cycles includes a polyp and a medusa stage
Body Plan
• Polyp: cylindrical body with arm-like tentacles; mouth points upward
• Medusa: motile, bell-shaped body; mouth on the bottom
Feeding
• Polyps and medusas have a body wall that surrounds an internal space: the gastrovascular cavity
• Gastrovascular cavity: a digestive chamber with one opening
– Food enters and wastes leave the body
Respiration, Circulation, & Excretion
• Following digestion, nutrients are usually transported throughout the body by diffusion
• Respire and eliminate wastes by diffusion through body walls
Response• Specialized sensory cells are used to gather
information from the environment
• Nerve net: loosely organized network of nerve cells that together allow cnidarians to detect stimuli
– Distributed uniformly throughout the body in most species
– In some species it is concentrated around the mouth or in rings around the body
Response
• Statocysts: groups of sensory cells that help determine the direction of gravity
• Ocelli: eyespots made of cells that detect light
Movement
• Hydrostatic skeleton: a layer of circular muscles and a layer of longitudinal muscles that enable cnidarians to move
Reproduction: Sexually and Asexually
• Polyps can reproduce asexually by budding
• External sexual reproduction
– The sexes are separate-each individual is either male or female
– Both egg and sperm are released into the water
Groups of Cnidarians
• Jellies (formerly jellyfishes)
• Hydras and their relatives
• Sea anemones
• Corals