Ch 38 – Phylum Arthropoda

1. Ch 38 – Phylum Arthropoda

2. Characteristics of Arthropods • Segmented (Arthropod means “jointed foot” • Body segments have jointed appendages • Exoskeleton • Provides protection and support • Made of 3 layers excreted by the epidermis • Outer layer – waxy, mix of proteins and lipids • Repels water and prevents dessication • Middle layer – primary protection, protein and chitin • Inner layer – flexible at joints, protein and chitin • Muscles attach to move body segments

4. Characteristics Cont’d • True Coelom • Bilateral symmetry • Cephalization • Variety of appendages around mouth • Most have segmented antennae at anterior • Compound eyes • Made of many individual light detectors • Sense light intensity • Send impulses to brain, then move along ventral nerve cord • Open circulatory system

5. Molting • B/c of exoskeleton, arthropods can’t grow without periodically shedding • In between molts: • Tissues swell to put pressure on exoskeleton • Hormone is released • Epidermis secretes enzymes to digest inner layer • Uses this material to build new exoskeleton • Outer layer loosens and breaks

6. Molting Cont’d • Takes days for new exoskeleton to become hard • Very vulnerable during this time

7. Evolution and Classification • ¾ of all animal species belong to this phylum • Extremely diverse • Lobsters, crabs, spiders, centipedes, insects, etc. • First appeared more than 600 mya • Various groups have undergone evolutionary changes • Scientists still believe they had a common ancestor • Ancestor: body segments identical, Living species: Specialized tagmata

8. Evolution and Classification Cont’d • Divided in 4 subphyla • Trilobita (extinct animals called trilobites) • Crustacea - Lobsters, crabs, crayfish, etc. • Have pair of chewing mouthparts - mandibles • Chelicerata– spiders, scorpions, ticks, etc. • No antennae, pincerlike mouthparts - chelicerae • Uniramia– centipedes, millipedes, insects • Have antennae and mandibles, appendages are unbranched

10. 38-2 Subphylum Crustacea

11. Characteristics • 2 pairs of appendages on head – feelers • Each other body segment generally has a pair of appendages • Some are branched

12. Characteristics Cont’d • Exoskeletons contain large amounts of CaCO3 • Gas exchange • Some through exoskeleton, some gills • Development • Most have free-swimming larva called a nauplius • 3 pair appendages, 1 eye • Takes adult form through series of molts

13. Characteristics - Size • Large range, but mostly small • Small • Copepods and Water fleas • Size of a comma • Copepods = ocean plankton • Large • Japanese Spider Crab • 14 foot leg span

14. The Crayfish • Freshwater relative of lobster • Decapod = 5 pairs of legs

15. External Structure • Body divided into 2 main parts • Cephalothorax • Consists of 2 tagmata • Head – 5 segments • Thorax – 8 segments, posterior to head • Dorsal exoskeleton fused into the carapace • Abdomen • Lies posterior to cephalothorax, 7 segments • 7th is called the telson, forms flat paddle

16. External Structure Cont’d • Pair of app. attached to each segment (except telson)See chart pg. 749 • Antennules and Antennae: feelers sensitive to touch, taste • Mandible: Chews food • Maxilla: 2 pairs, manipulate food, assist with respiration • Maxillipeds: 3 pairs, manipulate food, sensitive to touch and taste

17. External Structure Cont’d • Chelipeds: Most anterior on thorax, end in large pincers • For capturing food and defense • Walking leg: 4 pairs, movement over solid surface • First two pairs end in small pincers for grasping • Swimmeret: attached to five abdominal segments • Create water currents and used in reproduction • Uropod: On sixth abdominal segment, used for propulsion

18. Crayfish Ventral View

19. Crayfish - Digestion • Food passes through esophagus to stomach • Stomach grinds food into fine paste • Uses teeth made of chitin and CaCO3 • Paste mixed with enzymes excreted by a digestive gland • Moves through intestine (further digestion and absorption) • Waste leaves body via anus

20. Crayfish – Respiration • Use gills • Extend from base of each walking leg into chamber under carapace • Legs circulate water across gills during walking • Posterior pair of maxillae as well • Each gill covered by extension of exoskeleton • Thin enough for gas exchange

21. Crayfish - Circulation • Excess water eliminated through organs called green glands • Open circulatory system • Dorsal heart • Pumps hemolymph through vessels • Hemolymph enters hemocoel, bathing tissues • Passes through gills for gas exchange • Returns to heart

22. Crayfish – Nervous system • Brain (pair of ganglia) located above esophagus • Receives impulses from eyes, antennae, antennules • Nerves extend down to control mouth appendages • Ventral nerve cord runs posteriorly

23. 38-3 Subphylum - Chelicerata • Class Arachnida

24. Class: Arachnida • Includes spiders, scorpions, mites, & ticks • Body is divided into cephalothorax and abdomen (similar to crayfish) • Cephalothorax usually includes: • 6 pairs jointed appendages • 1 pair chelicerae (picher-like mouthparts) • 1 pair pedipalps • Aid in holding food and chewing • 4 pairs of walking legs

26. Spider Anatomy • Body is pinched b/t cephalothorax and abdomen • Chelicerae modified as fangs used to inject venom • Venom produced by poison glands in the CT • Flows through ducts in chelicerae to tips • Most have 8 simple eyes

27. Spider Anatomy cont’d • Posterior tip of abdomen has 3 pairs of organs called spinnerets • Each made of hundreds of microscopic tubes • Connect to silk glands in abdomen • Fluid made from protein hardens into threads as it is pulled from the spinnerets • Used to spin webs, build nests, protect eggs • Some move to a new habitat by allowing wind to pull their threads

29. Spider Anatomy Cont’d • Nervous, digestive, circulatory systems all very similar to crustaceans • Respiratory system is different (terrestrial!) • Book lungs: paired sacs in the abdomen with many folds for gas exhange And/or • Tracheae: system of tubes that carry air directly to tissues • Through openings in exoskeleton called spiracles

30. Spider Anatomy Cont’d • Excretory system – modified for land • Malpighian tubules: hollow projections of digestive tract • Collect body fluids and waste, carry to intestine • Most water reabsorbed, wastes leave body in solid form • Coxal glands • Organs that remove wastes and discharge them through openings at the base of some legs

31. Life of a Spider • Feed mostly on insects, some can catch fish frogs, or birds • Many predator adaptations • Chase, Trapdoor, Snare • Male usually smaller than female • As soon a sperm is transferred to female, the male moves away quickly • May get eaten if he isn’t fast enough • Female then puts fertilized eggs in silken case • Carries it or attaches it to something

32. Life of a Spider Cont’d • Most venom harmless to humans • only 2 fatal species in U.S. • Black Widow • Red/orange hourglass shaped mark ventral abdomen • Venom attacks nervous system • Brown Recluse • Violin shaped mark on dorsal cephalothorax • Venom digests tissues surrounding the bite

34. Scorpions • Differ from spiders in 2 ways • Large pincerlikepedipalps • Large stinger on the last abdomen segment • Curled over body • Usually nocturnal hunters • Prefer tropical or desert climates

35. chelicerae eyes pedipalp

36. Mites and Ticks • Completely fused CT and abdomen • Mites • Most less than 1 mm in length • Both free living and parasitic • Ticks • Range from a few mm to over an inch • Many parasitic • Can transmit Rocky Mountain Spotted Fever and Lyme disease

37. Mite and Tick Body Regions pedipalps & chelicerae cephalothorax abdomen

38. American dog tick male Blacklegged (deer) tick female

39. American dog tick female laying egg mass (1000-2000 eggs!).

40. Subphylum – Uniramia • Myriapods • Could have been first animals to appear on land • Highly segmented • Little variation to appendages • No waxy exoskeleton • Live in damp environment

41. Class – Diplopoda • Millipedes • 2 pairs of legs per segment • Adapted for burrowing through soil • Move slowly (legs are short) • Rounded bodies • Eat plant matter • Short antennae, 2 groups simple eyes • Bad vision, good sense of smell

42. Class – Chilopoda • Centipedes • 15-175 pairs of legs • 1 pair per segment • Can be very large in tropical regions • Flattened bodies • 1st segment app. modified as poison claws • Predatory • Move quickly in search of prey (earthworms, insects, etc.)