Chapter 14

1. Chapter 14 The Arthropods: Blueprint for Success

2. Evolutionary Perspective • Metamerism modified by tagmatization • Chitinous exoskeleton • Paired, jointed appendages • Ecdysis • Ventral nervous system • Coelom reduced to cavity around gonads • Open circulatory system • Complete digestive tract • Metamorphosis often present

3. Classification and Relationships to other Animals • Ecdysozoans • Cuticle, ecdysis, loss of epidermal cilia (figure 14.2) • Monophyletic with five subphyla (table 14.1) • Chelicerata, Crustacea, Hexapoda, Myriapoda, Trilobitomorpha (entirely extinct)

4. Figure 14.2 Evolutionary relationships of the arthropods to other animals.

5. Table 14.1

6. Metamerism and Tagmatization • Metamerism evident externally • Segmental body wall • Segmental appendages • Metamerism reduced internally • No septa • Most organs are not metameric • Tagmatization obvious • Specializations for feeding, sensory perception, locomotion, and visceral functions

7. Learning Outcomes: Section 14.3 • Describe the structure of the arthropod exoskeleton or cuticle. • Assess the influence the exoskeleton has had on the evolution of the arthropods.

8. The Exoskeleton • Exoskeleton or cuticle • External jointed skeleton • Functions • Structural support • Protection • Prevents water loss • Levers for muscle attachment and movement • Covers all body surfaces and invaginations • Secreted by epidermis (hypodermis)

9. The Exoskeleton • Epicuticle (figure 14.3) • Lipoprotein • Impermeable to water • Barrier to microorganisms and pesticides • Procuticle • Chitin • polysaccharide • Outer procuticle hardened by sclerotization or deposition of calcium carbonate • Inner procuticle less hardened and flexible • Articular membranes at joints (figure 14.4) • Modifications include sensory receptors • Sensilla

10. Figure 14.3 Arthropod exoskeleton.

11. Figure 14.4 Modifications of the exoskeleton.

12. The Exoskeleton • Growth accompanied by ecdysis (figure 14.5) • Enzymes from hypodermal glands begin digesting old procuticle (a, b). • New procuticle and epicuticle secreted (c, d). • Old exoskeleton splits (e) • Calcium carbonate deposition and/or sclerotization hardens new exoskeleton (f).

13. Figure 14.5 Events of ecdysis.

14. The Hemocoel • Embryonic blastocoel • Internal cavity for open circulatory system • Fluids bathe internal organs. • Exchange of nutrients, wastes, and sometimes gases • Not a hydrostatic compartment

15. Metamorphosis • Radical change in body form and physiology as an immature (larva) becomes an adult. • Reduces competition between adult and immature stages

16. Subphylum Trilobitomorpha • Dominant life form from Cambrian period (600 mya) to Carboniferous period (345 mya) • Substrate feeders • Three tagmata: head, thorax, and pygidium • Three longitudinal sections • Biramous appendages

17. Figure 14.6 Subphylum Trilobitomorpha (Saukia sp).

18. Subphylum Chelicerata • Spiders, mites, ticks, horseshoe crabs • Two tagmata • Prosoma • Eyes • Chelicerae • Often chelate • Usually feeding appendages • Pedipalps • Sensory, feeding, locomotion, reproduction • Walking legs • Opisthosoma • Digestive, reproductive, excretory, and respiratory organs

19. Class Meristomata Figure 14.7 A eurypterid, Euripterus remipes. • Subclasses • Eurypterida • Extinct giant water scorpions (figure 14.7)

20. Class Meristomata Figure 14.8a Limulus polyphemus. • Subclass Xiphosura • Horseshoe crabs • Limulus (Atlantic Ocean and Gulf of Mexico) • Book gills • Gas exchange between blood and water • Reproduction • Dioecious • External fertilization

21. Figure 14.8b Ventral view of Limulus.

22. Class Arachnida • Spiders, mites, ticks, scorpions • Arose from ancient euryptrids • Very early terrestrial groups • 280-400 mya • Exoskeleton was preadaptation for water conservation.

23. Form and Function • Carnivores • Chelicerae to hold prey or as fangs • Gut • Foregut • Cuticular • Pumping stomach • Hindgut • Cuticular • Water reabsorption • Midgut • Noncuticular • Secretion and absorption

24. Form and Function • Excretion • Coxal glands • Paired sacs bathed in blood of body sinuses • Homologous to nephridia • Excretory pores at base of posterior appendages • Malpighian tubules • Blind ending diverticula of gut tract • Empty via digestive tract • Uric acid

25. Form and Function • Gas Exchange • Book lungs • Paired ventral invaginations of body wall • Gas exchange between air and blood across book lung lamellae • Tracheae • Branched, chitin-lined tubes • Open at spiracles along abdomen

26. Figure 14.9 An arachnid book lung.

27. Form and Function • Circulation • Open with dorsal contractile vessel • Pumps blood into tissue spaces of hemocoel • Returns to dorsal vessel via ostia • Nervous system • Ventral with fusion of ganglia

28. Form and Function • Senses • Mechanoreceptors • Modifications of exoskeleton • Sensilla respond to displacement. • Chemical sense • Pores in exoskeleton • Vision • Eyes detect movement and changes in light intensity. Figure 14.10 An arthropod seta (a) and an eye (ocellus) (b).

29. Form and Function • Reproduction • Dioecious • Indirect sperm transfer • Male deposits spermatophores, which are transferred to the female. • Courtship rituals common • Copulation occurs in spiders via modified pedipalp of male. • Development • Direct

30. Order Scorpionida • Prosoma • Shieldlike carapace • Opisthosoma • Preabdomen • Postabdomen (“tail” with sting) • Courtship prior to mating • Oviparous, ovoviviparous, or viviparous

31. Figure 14.11 (a) Hardrurus arizonensis (b) External anatomy. (a) (b)

32. Order Araneae • Spiders • Prosoma • Chelicerae with poison glands and fangs • Pedipalps leglike • Sperm transfer in males • 6-8 eyes • Opisthosoma • Connected to prosoma via pedicel • Swollen or elongate • Visceral functions and spinnerets

33. Figure 14.12 External structure of Argiope.

34. Figure 14.13 Prosoma of a spiderling.

35. Order Araneae • Silk • Protein • Repeating sequence of glycine and alanine • Beta sheet • Stored as gel prior to spinning • Chemical modification when forced through spinnerets • Webs, line retreats, safety lines, wrapping eggs, dispersal of young (ballooning)

36. Figure 14.14 Members of the family Araneidae are the orb weavers.

37. Order Araneae • Feeding • Insects and other arthropods • Hunt or capture in webs • Paralyze prey • May wrap in silk • Inject enzymes into prey body wall • Two spiders are venomous to humans.

38. Figure 14.15 (a) Black widow spiders (Lactrodectus mactans) has a neurotoxic venom. (b) Brown recluse spiders (Loxosceles reclusa) have a histolytic venom. (b) (a)

39. Order Araneae • Reproduction • Complex behaviors • Chemical, tactile, and visual signals • Male’s pedipalps enlarged into embolus • Male deposits sperm on web and collects with pedipalps. • Transfers sperm to female during mating • Female deposits eggs in silk case. • In webbing, a retreat, or carries with her

40. Order Opiliones Figure 14.16 Order Opiliones (Leiobunum sp). • Harvestmen or daddy longlegs • Prosoma broadly joins opisthosoma • Legs long and slender • Omnivores • External and internal digestion

41. Order Acarina • Mites • Prosoma and opisthosoma fused and covered by single carapace • 1mm or less • Free-living • Herbivores or scavengers • Many pest species • Ectoparasites • Chigger (Trombicula) • Follicle mite (Demodex) Figure 14.17 Dermatophagoides farinae is common in homes and grain storage areas.

42. Order Acarina • Ticks • Ectoparasites in all life stages • Up to 3cm • Females lay eggs after engorging with blood. • Important in disease transmission • Rocky Mountain spotted fever • Lyme disease

43. Figure 11.18 Ixodes scapularis transmits the bacteria that causes Lyme disease.

44. Class Pycnogonida (Subphylum Cheliceriformes?) • Sea spiders • Marine • Feed on cnidarian polyps • Dioecious • Molecular, developmental, and morphological characters are being used to reevaluate taxonomic status. Figure 14.19 Class Pycnogonida

45. Subphylum Crustacea • Crayfish, shrimp, lobsters, crabs, copepods cladocerans and others • Almost all are aquatic • Terrestrial isopods and crabs are exceptions. • Two pairs of antennae • Biramous appendages (figure 14.20)

46. Figure 14.20 Crustacean body form. (a) External anatomy. (b) Biramous appendages.

47. Class Malacostraca • Crabs, lobsters, crayfish, shrimp, krill, amphipods, isopods • Order Decapoda • Largest order • Shrimp, crayfish, lobsters, crabs

48. Class Malacostraca • Crayfish external structure • Cephalothorax • Fusion of head and thorax • Covered dorsally and laterally by carapace • Sensory, feeding, locomotion • Abdomen • Muscular “tail” in crayfish • Locomotor and visceral functions in others • Paired appendages • Serially homologous (derived from a common ancestral pattern)

49. Figure 14.22 External structure of a male crayfish.

50. Figure 14.23 Serial homology of crayfish appendages.