Sponges and Cnidarians

Transcription

1 The Animal Kingdom Multicellular Sponges and Cnidarians Biology : Chapter 26 Eukaryotic Heterotrophs Cells lack cell walls 95% are invertebrates What Animals Do to Survive Feeding Response Respiration Circulation Movement Reproduction Excretion Jan 9 8:45 AM Trends in Animal Evolution Cell specialization and levels of organization Early development Body symmetry Cephalization Body cavity formation Jan 9 8:49 AM 1

2 Jan 9 8:51 AM Jan 9 9:02 AM SPONGES Jan 9 9:09 AM Phylum Porifera Sponges Have tiny openings, or pores, their bodies all over Sessile: they live their entire life single spot attached to a They are animals! Why? Jan 9 9:11 AM 2

3 animals chpt 26.notebook January 09, 2013 Form and Function in Sponges Sponges are Animals!!! Multicellular Heterotrophic Have nothing resembling a mouth or gut No cell walls Have no tissues or organ systems Contain a few specialized cells 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 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 Choanocytes Specialized cells that use flagella to move a steady current of water through the sponge Filters several thousand liters/day 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 3

4 Feeding Filter feeders Sift microscopic food from the water Particles are engulfed by that line the body cavity food from choanocytes 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 Reproduction No nervous system Many sponges protect themselves by producing toxins that make them unpalatable or poisonous to potential predators 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 Budding Asexual Reproduction Gemmules: groups of archaeocytes surrounded by spicules 4

5 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 Ecology of Sponges Attached to the seafloor and may receive little sunlight Some have spicules that look like cross shaped antennae Many are green due to these organisms living in their tissues Like a lens or magnifying glass, they focus and direct incoming sunlight CNIDARIANS Cnidarians Phylum Cnidaria Hydras, jellies, anemones, and corals sea 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 Nematocyst A poison filled, stinging structure that contains a tightly coiled dart Found within cnidocytes Used for defense and to capture prey 5

6 Form and Function in Cnidarians Only a few cells thick Radially Symmetrical Central mouth surrounded by numerous tentacles that extend outward from the body Life cycles includes a polyp and a medusa stage Simple body systems Most of their responses to the environment are carried out by specialized cells and tissues 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 wastes through body walls eliminate by diffusion 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 6

7 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 Groups of Cnidarians Jellies (formerly jellyfishes) Hydras and their relatives The sexes are separate each individual is either male or female Sea anemones Both egg and sperm are released into the water Corals Ecology of Corals The worldwide distribution is determined by: Temperature Water depth Light intensity Jan 6 9:38 PM Many suffer from human activity Coral bleaching has become common Global warming may add to the problem 7