The Invertebrates

1. The Invertebrates Romina Angelelli

2. 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 wall • Typically diploid • Most are invertebrates meaning no backbone

3. Animal Body Plans • Organization: • Different cells carry out different tasks within the animal • Cells are organized as tissues • Tissue formation begins in an embryo • At 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.

4. 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.

5. 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 coelom • Materials 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

6. 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 flow • Segmentation: • Many bilateral animals are segmented • When many segments specialize on the same tasks they cn change and take on new functions.

7. Animal Origins Adaptive Radiation • It 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 Australia’s Ediacaran hills and therefore called Ediacarans. • Most don’t 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.

8. 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.

9. Simplest Living Animal • Placozoan • Only one • Trichoplax adhaerens • No body symmetry • No tissues • 4 different type of cells • Marine animal • 2mm in diameter • Sticky, hairy plate • Smallest genome of any known animal • Close relative of choanoflagellates

10. Sponges • Phylum Porifera • Aquatic • No symmetry, tissue, or organs • Differ in shape and size • Non flagellated cells on the outside and flagellated collar cells within • Jellylike matrix between the cell layers • Intracellular digestion • Filter feeders • Serve as habitat • hermaphrodite • Phagocytosis

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

14. Flatworms • Platyhelminthes phylum • Planarians • Bilateral protostomes • the simplest animals to have organ systems. • Nerve cords connect to ganglia in the head and serve as control center • Saclike gut • Pharynx to take in food and expel waste • Tapeworms are parasitic flatworms. Their bodies are made of units called proglottids. Flukes are also parasites.

16. Annelids • Segmented worms (earthworms and polychaetes) and leeches • Circulatory digestive • Solute-regulating • Nervous systems extend through all coelomic chambers • Nephridia- regulate the composition of body fluid

17. Mollusks • Sheetlike mantle • Most have respiratory gills in the mantle cavity • Feed using a food scraping radula • 4 main classes • Chitons: has segmented plates • Gastropods: 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)

19. Rotifers and tardigrades • Tiny animals of damp or aquatic habitats • Rotifers- ciliated head and pseudocoelom • Tardigrades- (water bears) have a reduced coelom and molt • Both can dry out and survive for long periods of adverse conditions

20. roundworms • (Nematodes) • Unsegmented body • Molted cuticle • Complete gut • False coelom • Some are human parasites

21. Arthropods • Largest phylum of animals • Jointed exoskeleton • One or more pairs of sensory antennae in most • Malpighian tubules- expel waste in land-dwelling groups.

22. Arthropods • Chelicerates- 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 Earth’s biomass. Three part body, head, thorax, and abdomen. Undergo metamorphosis, the body form change between larval and adult stages.

23. Echinoderms • Invertebrates of the deuterostome lineage • Skin with spines, spicules, or plates of calcium carbonate. • Adults are radial • Water-vascular system- differentiated by tubefeet • eyespots

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