1. The Arthropods: Blueprint for Success

2. Evolutionary Perspective 1.Metamerism modified by tagmatization 2.Chitinous exoskeleton 3.Paired, jointed appendages 4.Ecdysis 5.Ventral nervous system 6.Coelom reduced to cavity around gonads 7.Open circulatory system 8.Complete digestive tract 9.Metamorphosis often present

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

4. 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

5. 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)

6. 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

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

8. 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

9. Subphylum Trilobitomorpha.

10. 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

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

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

13. Figure 14.8b Ventral view of Limulus.

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

15. 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

16. 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

17. 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

18. Figure 14.9 An arachnid book lung.

19. 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

20. Form and Function Senses – Chemical sense Pores in exoskeleton – Vision Eyes detect movement and changes in light intensity.

21. Form and Function Reproduction – 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

22. Order Scorpionida Prosoma – Shieldlike carapace Opisthosoma – Preabdomen – Postabdomen (“tail” with sting) Courtship prior to mating

24. 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

25. External structure of Golden Orb.

26. Prosoma of a spiderling.

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

29. 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.

30. (a) (b)

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

32. Order Opiliones Harvestmen or daddy longlegs Prosoma broadly joins opisthosoma Legs long and slender Omnivores External and internal digestion

33. 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)

34. 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

36. 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

37. 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)

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

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

40. 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)

41. Figure 14.22 External structure of a male crayfish.

42. Figure 14.23 Serial homology of crayfish appendages.

43. Class Malacostraca Crayfish internal structure – Digestive system Complete with foregut, midgut, and hindgut – Respiratory system Gills attach at base of cephalothoracic appendages. Lie within gill chamber between carapace and lateral body wall Second maxilla circulates water. – Circulation Open Dorsal heart and major arteries Blood enters hemocoel, and gills before returning to pericardial sinus around heart.

44. Figure 14.24 Internal structure of a crayfish.

45. Class Malacostraca Ventral nervous system – Cephalization and centralization – Supraesophageal and subesophageal ganglia process sensory information and control head appendages. – Segmental ganglia Sensory structures – Antennae – Compound eyes – Statocysts – Chemoreceptors – Proprioceptors – Tactile setae

46. Class Malacostraca Endocrine system – Ecdysis, sex determination, color change X-organs – Neurosecretory tissues in eyestalks – Molt-inhibiting hormone » Target Y-organ Y-organs – Base of maxillae – Releases ecdysone when molt inhibiting hormone is not present and ecdysis occurs – Androgenic glands (males) Promotes development of testes and male characteristics

47. Class Malacostraca Excretion – Antennal (green) glands in crayfish – Maxillary glands in others – Homologous to coxal glands of arachnids Reproduction – Dioecious – Mating after female molts Fertilized eggs attach to female’s pleopods Others have planktonic larvae

48. Figure 14.25 (a) Nauplius larva of a barnacle. (b) Zoea larvae of a crab. (a) (b)

49. Order Isopoda “Pillbugs” Aquatic and terrestrial Dorsoventrally flattened Figure 14.26a Order Isopoda.

50. Order Amphipoda Laterally compressed Crawl or swim on sides Beach-hoppers modified for jumping Figure 14.26b Order Amphipoda.

51. Class Branchiopoda Fairy shrimp – Temporary ponds Brine shrimp – Great Salt Lake Cladocera – Freshwater water fleas – Large carapace – Parthenogenesis common Flattened, leaflike appendages Figure 14.27 Order Cladocera.

52. Class Maxillopoda Subclass Copepoda – Most abundant crustaceans – Important in marine and freshwater food webs – First antennae modified for swimming Figure 14.1 Subclass Copepoda.

53. Class Maxillopoda Subclass Thecostracea, Infraclass Cirripedia – Barnacles – Marine – Monoecious Nauplius and cypris larvae Cypris larva settles and metamorphoses into sessile adult. – Some parasites

54. Figure 14.28 Class Maxillopoda, Infraclass Cirripedia. (a) Internal structure of an acorn barnacle. (b) A stalked barnacle (Lepas).

55. Further Phylogenetic Considerations Diverse body forms and lifestyles of Arthropoda arose from single ancestor. Crustaceans very successful in aquatic habitats Chelicerata – First terrestrial arthropods – Account for evolution of many water conserving features of the phylum Exoskeletal, excretory, and respiratory adaptations