Ch.14 The Arthropods

1. Ch.14 The Arthropods

3. Arthropod Characteristics • 70-85% of all named animals species are arthropods! The majority of which are insects (beetles, flies, wasps, butterflies) • Segmented invertebrates • Bilateral Symmetry • Protostome development • 3 main body segments: • Thorax: middle body region • Abdomen: posterior end • Cephalothorax: head

4. Arthropod Characteristics • Metamerism & Tagmatization • Chitinous exoskeleton-provides support & protection • Paired, jointed appendages • Grow by molting (ecdysis) • Ventral nervous system • Small coelom • Open circulatory system • Blood released into hemocoel (tissue space) • Complete digestive system • Metamorphosis usually present • Different body forms at different stages of development (reduces competition between immature and adult stages)

5. ExoskeletonProvides structural support, protection, impermeable surfaces for the prevention of water loss, and a system of levers for muscle attachment and movement. • Two layers: • Epicuticle – outermost layer • Waxy lipoprotein • Impermeable to water • Barrier to microorganisms & many pesticides • Procuticle – inner layer, thickest • Made up of Chitin (tough substance-think leather) • Hardens by sclerotization(hardening & tanning process)

6. Jointed Appendages • Appendages: structures, such as legs and antennae, that grow and extend from an animal’s body. • Arthropods have paired appendages. • Appendages of arthropods are adapted for a variety of functions such as feeding, mating, sensing, walking, and swimming. • Arthropod appendages are jointed-enable flexible movement.

7. Feeding & Digestion • The mouthparts of most arthropods include a pair of appendages called mandibles that can be adapted for biting or chewing. • Other arthropods have mouthparts modified like feathery strainers, stabbing needles, cutting swords, or sucking straws. • Arthropods can be herbivores, carnivores, filter feeders, omnivores, or parasites. • Arthropods have a complete, one way digestive system with a mouth, gut, and an anus, along with various glands that produce digestive enzymes.

8. Respiration • Gills • Most aquatic arthropods have gills that function in the same way as they do for mollusks • Tracheal tubes • Terrestrial arthropods, tubes branch into smaller and smaller tubules that carry oxygen throughout the body. • Book lungs • Saclike pockets with highly folded walls for respiration, folded walls increase surface area and allow for efficient exchange of gases. • Both tracheae and book lungs open to the outside of the body of the arthropod in openings called spiracles.

9. Excretion • Cellular wastes are removed from the blood through Malpighian tubules. • Malpighian tubules are attached to and empty into the gut, which contains the undigested food wastes to be eliminated from the body. • Crustaceans and some other arthropods do not have Malpighian tubules, they have modified nephridia, similar to those in annelids.

10. Response to Stimuli Vision: • Arthropods have large, compound eyes. • A compound eye has many facets, which are hexagonal in shape. • Each facet sees part of an image and the brain combines the images into a mosaic. • Compound eyes can detect the movements of prey, mates, or predators, and also can detect colors. • Many arthropods have 3-8 simple eyes as well as their compound eyes! (Only distinguishes light and dark)

11. Response to Stimuli • Chemicals: • Pheromones: chemicals secreted by many animal species that influence the behavior of other animals of the same species. • Arthropods give off a variety of pheromones that signal behaviors such as mating or feeding. • Hearing: • In addition to eyes, many arthropods also have another sense organ called a tympanum-a flat membrane used for hearing. • It vibrates in response to sound waves. • Arthropod tympanums can be located on the forelegs as in crickets, or on the abdomen as in some grasshoppers, or on the thorax as in some moths!

12. Reproduction • Most arthropods reproduce sexually and have a variety of adaptations for reproduction. • Most arthropods have separate sexes, but a few such as barnacles, are hermaphrodites and undergo cross-fertilization. • Most crustaceans brood, or incubate, their eggs in some way, but they do not care for their hatched offspring. • Some spiders and insects also incubate their eggs, and some, such as bees, care for their young!

13. Ecdysis (molting) • Four stages • 1. enzymes digest old procuticle • 2. new procuticle and epicuticle secreted • 3. old exoskeleton splits along predetermined lines when the animal stretches by air or water intake & then shedding occurs • 4. calcium carbonate deposits & sclerotization harden new exoskeleton Cicada Molting

14. Metamorphism • Reduces competition between adults and immature stages • Is a radical change in body form and physiology as an immature stage, usually called a larva, becomes an adult.

15. Taxonomy of Phylum Arthropoda: • Page 217, Table 14.1

16. Subphylum Trilobitomorpha • Extinct, lived in oceans 600 million years ago • Oval body & body could roll into a ball to protect its ventral surface! • 3 tagmata: • Head • Thorax • Pygidium

18. Subphylum Chelicerata • Means “many claws” • Tagmata: • Prosoma (Cephalothorax) • Anterior • sensory & feeding • Opisthosoma • Posterior to prosoma • Contains organs for reproduction, digestion, respiration, and excretion • Paired appendages – for locomotion • Chelicerae – pincerlike, feeding • Pedipalps – sensory, feeding • Paired walking legs

19. Class Merostomata • Giant water scorpion • Extinct • six-legged • about 5 feet long &3 feet wide

20. Class Merostomata • Horseshoe crabs • Only 4 species of horseshoe crabs live today, they were in existence 600mya • Can be found in the Gulf of Mexico! • 2 Chelicerae, 2 pedipalps, 6 chelate walking legs, 2 digging (or swimming) appendages • 5 pairs of book gills • Dioecious,external fertilization (congregate in intertidal areas to mate) • Oviparous – lays eggs • Eat small invertebrates

23. Class Arachnida • Order Scorpionida • Scorpions • Order Araneae • Spiders • Order Opiliones • Harvestmen (daddy longlegs) • Order Acarina • Ticks & mites

24. Scorpions • Mostly nocturnal • 2 small chelicerae near mouth, 2 large pedipalps with pincers, 8 walking legs • Most sting like a wasp, only a few have deadly venom • Dioecious, courtship can last hours, mating is internal • Most Ovoviviparous – internal but, large yolky eggs • Some Viviparous – mother provides nutrients for embryos • Development about 1.5 years for 20 to 40 young • After birth, young crawl onto mother’s back (one month)

25. Spiders • About 34,000 species (largest arachnid group) • 2 poisonous chelicerae with fangs, 2 pedipalps for sperm transfer, 8 walking legs • 6 to 8 eyes • 6 to 8 spinnerets eject silk • Silk protein comes out as a liquid, then hardens • Ballooning – using silk line to travel hundreds of kilometers • Bite prey, paralyze them, wrap them in silk, inject enzymes, & suck victim dry • Females attract males to web with pheromones • Internal fertilization & oviparous (egg outside body)

26. Black Widow Lactrodectusmactans*Recognized by its shiny black body with a red hourglass pattern on its ventral surface*Neurotoxin: “nerve poison” can cause paralyses, difficulty of breathing, vomiting, fever, & sweating

27. Brown RecluseLoxoscelesreclusa • Hemotoxin: destroys red blood cells, disrupts blood clotting, and causes tissue damage. • Recognized by the dark brown, violin-shaped mark on the dorsal surface.

28. Daddy Longlegsor Harvestmen • Long legs • Most are omnivores, some predators • Not harmful to humans

30. Mites & Ticks • Mites 1mm or less • Free-living are herbivores & scavengers • Ectoparasites, most stay attached a few hours or days • Chigger (redbug) larvae burrow in skin, drop off to molt • Harmless follicle mite is permanent-most of us actually have this mite! • Itch mite causes Scabies (skin disease that causes extreme itching) • Ticks up to 3cm • Ectoparasitesall throughout their life • Copulation on host, females drop to ground to lay eggs

31. Chigger

32. Scabies

33. Tick

34. Class Pycnogonida • Sea spiders • All Marine and most common in cold water • Predators • Dioecious and males carry eggs until they hatch!

35. Subphylum Crustacea • Class Malacostraca • Crabs, lobsters, crayfish, shrimp, krill, isopods, amphipods • Class Branchiopoda • Fairy shrimp, brine shrimp, water fleas • Class Maxillopoda • Copepods, barnacles

36. Class MalacostracaGreek “malakos”=soft + “ostreion”=shell • Crabs, lobsters, crayfish, shrimp, krill, isopods, amphipods • Omnivores & scavengers • Have gills • Hemocoel present • Compound eyes on movable eye stalks • Dioecious (except for barnacle) • Abdomen is reduced and is held beneath the Cephalothorax • Head & Thorax (using crayfish as example) • 2 pairs of antennae, grinding mandibles, 2 pair maxillae, 3 pairs of maxillipeds, 5 pairs of walking legs (1st is large and chelate), males have an extra 2 pairs of claspers), 5 pairs of swimmerets, telson with uropods(flipperlike)

39. Reproduction • Dioecious • Males flip females over and deposit sperm • “Sticky” eggs develop on tale of female • Larval stages can lasts months

40. Class Branchiopoda • Fairy shrimp & brine shrimp • Mostly freshwater • During droughts, embryos become dormant in capsules • Water fleas (Daphnia!) • Look like fleas with large carapace • In spring, females reproduce parthenogenetically (without fertilization) • In winter, sexual reproduction produces winter eggs that hatch in spring

41. Class Maxillopoda • Copepods • Some or the most abundant crustaceans • Marine and freshwater • Few live on substrate and filter feed, some are predatory, others are parasites • Barnacles • Sessile adults • Marine only and ~1,00 species • Filter-feeders • Mostly monoecious • Many will colonize ships and boats, rocks, and even other animals, like whales!

44. Subphylum Myriapoda • 4 Classes: • Diplopoda (millipedes) • Chilopoda (centipedes) • Symphyla (symphylans) • Pauropoda (pauropodans)

45. Class DiplopodaMillipedes • Have 11-100 trunk segments • 2 pairs of appendages on each trunk segment • Worldwide in distribution and are found in or under leaf litter or decaying logs • Feed on decaying plant matter • Millipedes roll into ball when disturbed

46. Class ChilopodaCentipedes • Mostly nocturnal • Scurry about the surfaces of logs, rocks, or other forest-floor debris • Single pair of long legs on each segment • 15 or more trunk segments • Fast-moving predators • Food is small arthropods, earthworms, and snails and sometimes even frogs and rodents • Poison claws kill or immobilize prey…most venom is harmless to humans, although many have bites comparable to a wasp and a few human deaths have been reported from large, tropical species • Legs and segments are added with each molt