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Sponges and Cnidarians
Biology II: Chapter 26
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The Animal Kingdom Multicellular Eukaryotic Heterotrophs
Cells lack cell walls 95% are invertebrates
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What Animals Do to Survive
Feeding Respiration Circulation Excretion Response Movement Reproduction
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Trends in Animal Evolution
Cell specialization and levels of organization Early development Body symmetry Cephalization Body cavity formation
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SPONGES
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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…?
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Sponges are Animals!!! Multicellular Heterotrophic No cell walls
Contain a few specialized cells
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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
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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
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Choanocytes Specialized cells that use flagella to move a steady current of water through the sponge Filters several thousand liters/day
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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
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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
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Feeding Filter feeders Sift microscopic food from the water
Particles are engulfed by choanocytes that line the body cavity
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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
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Response No nervous system
Many sponges protect themselves by producing toxins that make them unpalatable or poisonous to potential predators
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Reproduction Sexually or asexually
A single spore forms both eggs and sperm; usually at different times
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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
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Asexual Reproduction Budding
Gemmules: groups of archaeocytes surrounded by spicules
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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
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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
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CNIDARIANS
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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
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Cnidocytes Stinging cells that are located on their tentacles
Used for defense and to capture prey
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Nematocyst A poison-filled, stinging structure that contains a tightly coiled dart Found within cnidocytes
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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
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Radially Symmetrical Central mouth surrounded by numerous tentacles that extend outward from the body Life cycles includes a polyp and a medusa stage
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Body Plan Polyp: cylindrical body with arm-like tentacles; mouth points upward Medusa: motile, bell-shaped body; mouth on the bottom
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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
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Respiration, Circulation, & Excretion
Following digestion, nutrients are usually transported throughout the body by diffusion Respire and eliminate wastes by diffusion through body walls
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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
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Response Statocysts: groups of sensory cells that help determine the direction of gravity Ocelli: eyespots made of cells that detect light
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Movement Hydrostatic skeleton: a layer of circular muscles and a layer of longitudinal muscles that enable cnidarians to move
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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
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Groups of Cnidarians Jellies (formerly jellyfishes)
Hydras and their relatives Sea anemones Corals
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Ecology of Corals The worldwide distribution is determined by:
Temperature Water depth Light intensity Many suffer from human activity Coral bleaching has become common Global warming may add to the problem
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