Invertebrates

1. Invertebrates Anatomy and Physiology in Invertebrates

2. Support and Movement • Almost all animals have muscle-like tissue for movement • Three types of skeletons: • Hydrostatic skeleton • Exoskeleton • Endoskeleton

3. Hydrostatic Skeleton • Muscles supported by a water-filled body cavity • No hard structures for muscles to pull against • Push against the water in the body cavity • Cnidarians, flatworms, nematodes, mollusks, annelids

4. Exoskeleton • External skeleton, muscles attached inside • Arthropods have exoskeletons made of chitin • Exoskeletons are thin and flexible at joints, allowing for flexion and extension • Very adaptable, very strong • Drawbacks are that the animal must shed it and grow a new one as it gets larger, and it is heavy

5. Endoskeleton • Present in sponges and echinoderms (also in vertebrates) • Internal skeleton

6. Feeding and Digestion • Intracellular digestion vs extracellular digestion • Sponges filter food particles from the water and digestion is intracellular with nutrients being distributed among cells

7. Feeding and Digestion • Cnidarians and flatworms have a gastrovascular cavity • Digestive sac with a single opening – food enters, wastes leave • Food particles broken down into smaller pieces, then are taken up by cells lining the cavity and digestion is intracellular

8. Feeding and Digestion • Extracellular digestion takes place in annelids, mollusks, arthropods, invertebrate chordates • Tube within a tube digestive system – food enters through mouth and leaves through anus, digestive tract forms a separate tube within the body • Food is digested extracellulary in digestive tract and nutrients are absorbed

9. Internal Transport • Constant supply of oxygen and nutrients necessary for survival • Carbon dioxide and posionous wastes need to be eliminated • Invertebrates like sponges, cnidarians, flatworms, and nematodes do not have circulatory systems – all done by diffusion

10. Internal Transport • More complex invertebrates (and vertebrates) have circulatory systems, which include one or more pumps and tubes that move things around within the body • Open and closed circulatory systems

11. Open Circulatory System • Blood from heart is not entirely contained within blood vessels • Heart pumps blood through a series of vessels, and it is released directly onto body tissues • Flows through tissues and is collected in sinuses, eventually flowing back to heart • Seen in some types of mollusks (clams, oysters), arthropods, echinoderms

12. Closed Circulatory System • Blood contained within a system of closed vessels that pass through various parts of the body and return to the heart • Blood does not come in direct contact with tissues – more rapid and efficient • Seen in some mollusks (squids, octopuses), and annelids

13. Respiration (gas exchange) • Small soft-bodied invertebrates exchange oxygen and carbon dioxide by diffusion through body surfaces • Two respiratory problems: • Respiratory system must have large surface area to allow for enough gas exchange to support organism’s demands • Surface of organs must be kept wet because diffusion can only take place across moist membranes

14. Respiration (gas exchange) • Animals that live in water do not have these problems (sponges, cnidarians, flatworms, nematodes, echinoderms) • Mollusks and crustaceans have gills, which are rich in blood vessels and provide a large surface area for gas exchange

15. Respiration (gas exchange) • Terrestrial invertebrates have special organs for breathing air • Spiders have book lungs – sheet-like layers of thin tissue that contain blood vessels • Insects have trachea – tubes that bring air to each body cell

16. Excretion (waste elimination) • Related to maintaining proper water balance • Ammonia is a highly toxic, water soluble byproduct of the breakdown of amino acids – carried in blood and body fluids • Eliminating ammonia means eliminating water

17. Excretion (waste elimination) • Marine invertebrates (like sponges, cnidarians) have thin bodies and get rid of ammonia by diffusion through body surfaces or gill surfaces • Freshwater flatworms have flame cells, which remove water and water soluble wastes • Flame cells form a network that empties water and wastes through opening in the skin • Can also diffuse waste

18. Excretion (waste elimination) • Annelids, mollusks, invertebrate chordates have nephridia – structures that remove wastes from body fluids and return water and solutes to the body • Waste products eliminated as urine

19. Excretion (waste elimination) • Land invertebrates convert ammonia into urea (less toxic) which is concentrated into urine and expelled • Insects and some spiders convert ammonia into uric acid, which is removed by Malpighian tubules – uric acid excreted with solid waste, conserving water

20. Response • All animals have some sort of nervous system, with individual nerve cells functioning the same • Primitive invertebrates have a nerve net spreading through their body • Some cnidarians (jellyfish) show centralization where nerve cells are more concentrated, forming nerve cords or rings around the mouth

21. Response • Cephalization comes with concentrations of nerve and sensory cells in the head • Primitive flatworms have ganglia (clumps of nerve cells) while insects and some mollusks have actual brains • Brains lead to nerve cords

22. Response • Along with nervous development comes increased sensory development • Flatworms have eye spots • Insects have well developed, compound eyes

23. Reproduction • All invertebrates are capable of sexual reproduction, though some also reproduce asexually • Sexual reproduction creates and helps maintain genetic variation