Arthropods and Echinoderms

1. Biology I: Chapter 28 Arthropods and Echinoderms

2. ARTHROPODS

4. Arthropods • Phylum Arthropoda • Insects, crabs, centipedes, spiders • Segmented body • Tough exoskeleton made of chitin • Jointed appendages

5. Evolution of Arthropods • Fewer body segments • Highly specialized appendages for feeding, movement and other functions

6. Form and Function in Arthropods • Complex organ systems; some only found only in this phylum • Tracheal tubes (respiration) • Open circulatory system • Excrete wastes through saclike tubules

7. Feeding • Herbivores, carnivores, omnivores, bloodsuckers, filter feeders, detritivores, and parasites • Mouthparts have evolved to allow them to eat anything imaginable • Pincers or fangs to sickle-shaped jaws that can cut through the tissues of captured prey

8. Respiration: Terrestrial Arthropods • Tracheal tube: one of many branching, air-filled tubes that extend throughout the body • Spiracle: small opening located along the side of the body through which air enters and leaves the body • Book lung: organ that has layers of respiratory tissue stacked like the pages of a book: used to exchange gases

9. Respiration: Aquatic Arthropods • Respire through feather-like gills (i.e. lobster and crabs) • The horseshoe crab respires through organs: book gills

10. Circulation • Open circulatory system • Well-developed heart pumps blood through arteries that branch and enter the tissues • Blood leaves the blood vessels and moves through sinuses, or cavities • The blood recollects in a large sinus surrounding the heart • It reenters the heart and is again pumped throughout the body

11. Excretion • Terrestrial Arthropods • Malpighian tubules: sac-like organ that extracts wastes from the blood and adds them to feces that move through the gut Aquatic Arthropods • Diffusion moves cellular wastes from the arthropod’s body into the surrounding water

12. Response • Well-developed nervous system • Brain • Sophisticated sense organs, (i.e. eyes and taste receptors)

13. Movement • Well-developed groups of muscles that are coordinated and controlled by the nervous system • Allows arthropods to beat their wings against the air to fly, push their legs against the ground to walk, or beat their flippers against the water to swim

14. Reproduction • Terrestrial Arthropods • Internal fertilization • Sperm or sperm packet Aquatic Arthropods • Internal or external fertilization

15. Growth and Development in Arthropods • Molting • As the time for molting approaches, skin glands digest the inner part of the exoskeleton and other glands secrete a new skeleton • The animal pulls itself out of the remains of the original skeleton…this can take several hours • The new exoskeleton is soft and the animal is vulnerable to predators

16. Groups of Arthropods • Classified based on the number and structure of their body segments and appendages-particularly their mouthparts • Crustaceans • Spiders and their relatives • Insects and their relatives

17. Crustaceans • 2 pairs of branched antennae • 2-3 body sections • Mandibles: chewing mouthparts • Primarily aquatic • Examples: Crabs, shrimps, lobsters, crayfishes, and barnacles • Range in size from small terrestrial pill bugs to spider crabs that have masses around 20 kg

18. Crustaceans • Cephalothorax: region of a crustacean formed by the fusion of the head with the thorax • Thorax: body part of crustacean that lies just behind the head and houses most of the internal organs • Abdomen: posterior part of an arthropod’s body

19. Crustaceans • Carapace: the part of the exoskeleton that covers the cephalothorax • Mandible: mouthpart adapted for biting and grinding food • Cheliped: one of the first pair of legs of decapods (five pairs of legs: crayfishes, lobsters and crabs) • Swimmerets: flipper-like appendages used by decapods for swimming

20. Spiders and Their Relatives • Chelicerates • Mouthparts: chelicerae • 2 body sections • 4 pairs of walking legs • Horseshoe crabs, spiders, ticks, and scorpions

21. Horseshoe Crabs • The oldest living arthropods • First appeared more than 500 mya and have changed little since that time • Not true crabs at all! Anatomy is closer to that of spiders • Chelicerae, five pairs of walking legs, a long spike-like tail used for movement

22. Arachnids: Spiders • The largest group of arachnids • Spin webs of a strong, flexible protein called silk • Do not have jaws for chewing: must liquefy food to swallow it

23. Arachnids: Spiders • Chelicerae: pair of mouthparts in chelicerates that contain fangs and are used to stab and paralyze prey • Pedipalps: pair of mouthparts in chelicerates that are usually modified to grab prey • Spinneret: organ in spiders that contains silk glands

24. Arachnids: Mites and Ticks • Small arachnids that are usually parasitic • Chelicerae and pedipalps are specialized for digging into a host’s tissues and sucking out blood or plant fluids • Mouthparts are so strong that if you try to pull off a tick the cephalothorax may separate from the abdomen and remain in your skin

25. Arachnids: Scorpions • Widespread in warm areas around the world • Have pedipalps that are enlarged into claws • The long, segmented abdomen of a scorpion carries a venomous stinger that can kill or paralyze prey • Chew their prey using their chelicerae

26. Insects and Their Relatives • Uniramians have jaws, one pair of antennae, and unbranched appendages • A group that contains more species than any other group of animals living today • Wide variety of forms and lifestyles • Centipedes • Millipedes

28. Insects • Have a body divided into three parts: • Head • Thorax • Abdomen • Three pairs of legs are attached to the thorax • Like all arthropods, insects have a segmented body, exoskeleton, and jointed appendages

29. Responses to Stimuli • Multiple of sense organs are used to respond to stimuli • Compound eyes • Chemical receptors for taste and smell on their mouthparts • Well-developed ears that hear sounds far above the human range

30. Adaptations for Feeding • Three pairs of appendages that are used as mouthparts, including a pair of mandibles • Adaptations for feeding are not restricted to their mouthparts • Many produce saliva containing digestive enzymes that help break down food

31. Movement and Flight • 3 pairs of legs • Used for walking, jumping, flying, capturing and holding prey, etc. • The evolution of flight has allowed insects to disperse long distances and to colonize a wide variety of habitats

32. Metamorphosis • Incomplete metamorphosis: type of insect development characterized by a similar appearance throughout all stages of the life cycle • Nymph: immature form that lacks functional sex organs and other adult structures

33. Metamorphosis • Complete metamorphosis: type of insect development in which the larvae look and act nothing like their parents and also feed in completely different ways • Pupa: stage of metamorphosis in which an insect changes from a larva into an adult

34. Insects and Humans • Many insects are known for their negative effects • Termites destroy wood structures, moths eat their way through wool clothing, etc. • Despite their association with destruction and disease, insects contribute to agriculture by pollinating 1/3 of the food that you eat • Produce commercially valuable silk, wax and honey

35. Insect Communication • Communicate using sound, visual, chemical, and other types of signals • Much of the communication involves finding a mate • Pheromones: specific chemical messengers that affect the behavior of development of other individuals of the same species

36. Insect Societies • Ants, bees, termites, and some of their relatives form complex associations called societies • Society: a group of closely related animals of the same species that work together for the benefit of the whole group • Caste: group of individual insects specialized to perform particular tasks, or roles

37. ECHINODERMS

39. Endoskeleton: internal skeleton; hardened plates of calcium carbonate Five-part radial symmetry Echinoderms • Phylum Echinodermata • Live only in the sea • Spiny skin • Water vascular system • Tube feet: suction-cuplike structures

40. Form and Function in Echinoderms • The water vascular system, which is filled with fluid, carries out many essential body functions in echinoderms including respiration, circulation, and movement • Madreporite: sieve-like structure through which the water vascular system of an echinoderm opens to the outside

41. Feeding • Several methods of feeding • Sea urchins use five-part jaw-like structures to scrape algae from rocks • Sea lilies use tube feet to capture floating plankton • Sea stars feed on mollusks by pushing the stomach out through the mouth

42. Respiration and Circulation • Other than the water vascular system, echinoderms have few adaptations to carry out respiration or circulation • In most species, the thin-walled tissue of the tube feet provides the main surface for respiration

43. Excretion • Solid wastes are released as feces through the anus • Nitrogen-containing cellular wastes are excreted primarily in the form of ammonia • It is passed through the tube feet and skin gills

44. Response • Do not have a highly developed nervous system • Most have a nerve ring that surrounds the mouth and radial nerves that connect the ring with the body sections • Most have scattered sensory cells that detect light, gravity, and chemicals released by potential prey

45. Movement • Most move by tube feet and thin layers of muscle fibers attached to their endoskeleton • Mobility is determined by the kind of endoskeleton

46. Reproduction • Reproduce by external fertilization • The sexes are separate in most sea star species

47. Groups of Echinoderms • 7000 species • Sea urchins and sand dollars • Brittle stars • Sea cucumbers • Sea stars • Sea lilies and feather stars

48. Ecology of Echinoderms • Common in a variety of marine habitats • A rise or fall of echinoderms can cause major changes to populations of other marine organisms • Sea urchins control the distribution of algae and other forms of marine life • Sea stars are important carnivores that control the numbers of other organisms such as clams and corals