The Invertebrates

The Invertebrates Romina Angelelli What is an animal?Multicelled heterotrophs that move about while some are sessile but only for part of their life. Body cells do not have a wallTypically diploid Most are invertebrates meaning no backbone

Animal Body PlansOrganization: Different cells carry out different tasks within the animalCells are organized as tissuesTissue formation begins in an embryoAt first embryos had two tissue layers the outer ectoderm and the inner endoderm. (jellyfish and flatworms still do)Now a new layer called the mesoderm has evolved. It lays between both of the original layers and allows for increased complexity of the organism as well as organs. Animal Body Plans continued.Body Symmetry:Assymetrical (ex. Sponges)Radial Symmetry (ex. Jellyfish)Bilateral Symmetry (ex. Lobster)Most Bilateral animals have gone through cephalization. Meaning nerve cells have been concentrated at the head end. In some cases (lineages), evolved into a brain. Animal Body Plans continued.Gut and Body Cavity:Most animals have a gut. Saclike gut= incomplete digestive system, food enters and waste leaves through same opening.Tubular gut= complete digestive system, mouth at one and and an anus at the other. Perform several tasks simultaneously. Like taking in food, absorbing nutrients, etc. In most animals a fluid filled body cavity surrounds the gut. If surrounded by mesoderm it is the coelom. If incompletely lined it is the pseudocoel (false coelom). Advantages of Pseudocoel or coelomMaterials can diffuse through fluid to body cells.Muscles can redistribute fluid to alter body shape and locomotion.Organs can grow larger and more freely. Differences in digestive system of two major lineages of bilateral animals Protostomes: first opening that develops in embryo is mouth Deutrostomes: first opening to develop in embryo is anus

Animal Body Plans continued.Circulation: In small animals, gases and nutrients can diffuse through a body but in larger animals more is necessary to maintain them alive, a circulatory system.Circulatory system:Closed- A heart or hearts propel blood through a continuous system of vessels. Materials diffuse out into cells.Open- blood leaves vessels and exchanges materials directly with tissues before returning to the heart.Closed system= faster blood flowSegmentation:Many bilateral animals are segmentedWhen many segments specialize on the same tasks they cn change and take on new functions. Animal OriginsAdaptive RadiationIt is said that animals most likely evolved from a colonial protist similar to choanoflagelletes.Studies have shown that these protists have proteins similar to those in animals. Fossils of early animals that lived in the seas 570 million years ago were found in Australias Ediacaran hills and therefore called Ediacarans. Most dont have any living descendants. Several million years later animals underwent a dramatic adaptive radiation and by the end of the period all major animal lineages were present in the seas. Speciation occurred and all type of mutations were occurring as well. Relationships and classification Animals have traditionally been classified based on morphology and developmental patterns.The traditional classification method puts a lot of emphasis on possession of a body cavity.Recently gene sequence comparisons have been used to investigate relationships. Relationships amongst animals are still being investigated. Ex: recent genetic studies suggest that all invertebrates that molt are closely related.Simplest Living AnimalPlacozoanOnly oneTrichoplax adhaerensNo body symmetryNo tissues 4 different type of cells Marine animal2mm in diameter Sticky, hairy plateSmallest genome of any known animal Close relative of choanoflagellatesSpongesPhylum PoriferaAquaticNo symmetry, tissue, or organsDiffer in shape and sizeNon flagellated cells on the outside and flagellated collar cells within Jellylike matrix between the cell layersIntracellular digestionFilter feedersServe as habitathermaphroditePhagocytosis

CnidariaCnidarians have nematocysts in their tentacles Nematocysts- stinging cells Nematocysts help capture prey and also function as a defenseCreate a nerve net when interconnecting nerve cells extend through the tissuesFour classes: hydrozoans, anthozoans, cubozoans, and scyphozoans. Two tissues with a jellylike layer that functions as a hydrostatic skeleton between them.

FlatwormsPlatyhelminthes phylumPlanariansBilateral protostomesthe simplest animals to have organ systems. Nerve cords connect to ganglia in the head and serve as control centerSaclike gutPharynx to take in food and expel wasteTapeworms are parasitic flatworms. Their bodies are made of units called proglottids. Flukes are also parasites.

AnnelidsSegmented worms (earthworms and polychaetes) and leechesCirculatory digestiveSolute-regulatingNervous systems extend through all coelomic chambersNephridia- regulate the composition of body fluid

MollusksSheetlike mantle Most have respiratory gills in the mantle cavity Feed using a food scraping radula4 main classes Chitons: has segmented platesGastropods: have a distinct head that usually has eyes and sensory tentacles. Gastropods undergo torsion which is a unique rearrangement of body parts. (snails)Bivalves: hinged two part shells. Adductor muscles hold both valves together. (oysters, mussels, clams, etc.) Cephalopods: closed circulatory system, the smartest and fastest group of mollusks. (squids, octopuses, and relatives)

Rotifers and tardigradesTiny animals of damp or aquatic habitatsRotifers- ciliated head and pseudocoelomTardigrades- (water bears) have a reduced coelom and moltBoth can dry out and survive for long periods of adverse conditions

roundworms(Nematodes)Unsegmented bodyMolted cuticle Complete gutFalse coelom Some are human parasites

ArthropodsLargest phylum of animals Jointed exoskeletonOne or more pairs of sensory antennae in most Malpighian tubules- expel waste in land-dwelling groups.

ArthropodsChelicerates- cephalothorax, abdomen, four pairs of walking legs, eyes but no antennae. (horseshoe crabs and arachnids)Crustaceans- mostly marine. Two pairs of antennae. (wood lice, crabs, )Myriapods- predatory centipedes and scavenging millipedes. Many feet. Long body with similar segments, pair of antennae, and two simple eyes. Insects- over a million species. Most diverse group of arthropoda. Ants alone make up 10% of Earths biomass. Three part body, head, thorax, and abdomen. Undergo metamorphosis, the body form change between larval and adult stages.Echinoderms Invertebrates of the deuterostome lineage Skin with spines, spicules, or plates of calcium carbonate. Adults are radialWater-vascular system- differentiated by tubefeeteyespots

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