Animal Body PlansConstraints Imposed by Animal Body PlansPhysical laws constrain animal formBody size and shape affect interactions with the environmentAggregate Body PlansSponges are sessile with porous bodiesSpongesConstraints Imposed by Aggregate Body PlanBlind Sac Body PlansPhylum Cnidaria: radial symmetry and a gastrovascular cavityCorals, Anenomes, Hydroids and Jelly Fish - Phylum CnidariaPhylum Ctenophora: Comb jellies possess rows of ciliary platesComb Jellies – Phylum CtenophoraFlatworms (Phylum Platyhelminthes)Constraints Imposed by Blind Sac Body PlansTube within a tube Body PlansAdvantages of Tube within a Tube Body PlansSegmented Body PlansEvolution of the ExoskeletonMolluscan Body PlanArthropod Body PlanEchinoderm Body PlanPhylum – Echinodermata (starfish, urchins, sea cucumbers, crinoids, sand dollars, sea biscuits, etc.)Animal Body Plans• Aggregate• Blind sac• Tube-within-a-tube• Segmented• Molluscan• Arthropod• Sponges• Cnidaria, Ctenophora, Platyhelminthes• Acoelomate -Eucoelomate• Annelid• Mollusca• ArthropodaConstraints Imposed by Animal Body Plans•Size• Exchange of substances with the environment (diffusion, separation of alimentary and excretory pores) • Movement/Locomotion• Feeding and Foraging • Habitat/EnvironmentPhysical laws constrain animal form• Physical requirements constrain what natural selection can “invent,” including the size of single cells.– This prevents an amoeba the size of a pro wrestler engulfing your legs when wading into a murky lake.– An amoeba the size of a human could never move materials across its membrane fast enough to satisfy such a large blob of cytoplasm.– In this example, a physical law - the math of surface-to-volume relations - limits the evolution of an organism’s form.Body size and shape affect interactions with the environment• An animal’s size and shape have a direct effect on how the animal exchanges energy and materials with its surroundings.– As a requirement for maintaining the fluid integrity of the plasma membrane of its cells, an animal’s body must be arranged so that all of its living cells are bathed in an aqueous medium.– Exchange with the environment occurs as dissolved substances diffuse and are transported across the plasma membranes between the cells and their aqueous surroundings.• For example, a single-celled protist living in water has a sufficient surface area of plasma membrane to service its entire volume because it is so small.– A large cell has less surface area relative to its volume than a smaller cell of the same shape.– These considerations place a physical constraint on cell size.Aggregate Body Plans• Porifera (Sponges) (9000 species mostly marine, 100 species in fresh water)Sponges are sessile with porous bodies• The germ layers of sponges are loose federations of cells, which are not really tissues because the cells are relatively unspecialized.• Sponges are sessile animals that lack nerves or muscles. Individual cells sense and react to changes in the environment.• The body of a simple sponge resembles a sac perforated with holes.– Water is drawn through the pores into a central cavity, the spongocoel, and flows out through a larger opening, the osculum.• Nearly all sponges are suspension feeders, collecting food particles from water passing through food-trapping equipment.– Flagellated choanocytes, or collar cells, line the spongocoel (internal water chambers) create a flow of water through the sponge with their flagella, and trap food with their collars.• The body of a sponge consists of two cell layers separated by a gelatinous region, the mesohyl.• Wandering though the mesohyl are amoebocytes.– They take up food from water and from choanocytes, digest it, and carry nutrients to other cells.– They also secrete tough skeletal fibers within the mesohyl.• In some groups of sponges, these fibers are sharp spicules of calcium carbonate or silica.• Other sponges produce more flexible fibers from a collagen protein called spongin.– We use these pliant, honeycombed skeletons as bath sponges.SpongesConstraints Imposed by Aggregate Body Plan• Sessile (immobile)• Size limitation (I cm to 2 m for Sponges)• No separation of consumption and excretion• Little opportunity for specialization of functions• Restricted to Aquatic/Marine EnvironmentBlind Sac Body Plans• Cnidaria (anenomes, jellyfish, corals, hydroids)• Ctenophora (Comb jellies)• Platyhelminthes (Flatworms)• Multicellular animals are composed of microscopic cells, each with its own plasma membrane that acts as a loading and unloading platform for a modest volume of cytoplasm– This only works if all the cells of the animal have access to a suitable aqueous environment.– For example, a hydra, built on the blind sac plan, has a body wall only two cell layers thick.– Because its gastrovascularcavity opens to the exterior, both outer and inner layers of cells are bathed in water.Phylum Cnidaria: radial symmetry and a gastrovascular cavity• The cnidarians (hydras, jellies, sea anemones, and coral animals) have a relatively simple body construction.• They are a diverse group with over 10,000 living species, most of which are marine.• The basic cnidarian body plan is a sac with a central digestive compartment, the gastrovascular cavity.• This basic body plan has two variations: the sessile polyp and the floating medusa.• The cylindrical polyps, such as hydras and sea anemones, adhere to the substratum by the aboralend and extend their tentacles, waiting for prey.• Medusas (also called jellies) are flattened, mouth-down versions of polyps that move by drifting passively and by contacting their bell-shaped bodies.• Muscles and nerves exist in their simplest forms in cnidarians.• Cells of the epidermis and gastrodermis have bundles of microfilaments arranged into contractile fibers.– True muscle tissue appears first in triploblastic animals.– When the animal closes its mouth, the gastrovascularcavity acts as a hydrostatic skeleton against which the contractile cells can work.• Movements are controlled by a noncentralizednerve net associated with simple sensory receptors that are distributed radially around the body.• The three cnidarian classes show variations on the same body theme of polyp and medusa.Corals, Anenomes, Hydroids and Jelly Fish - Phylum CnidariaPhylum Ctenophora: Comb jellies possess rows of