1. Invertebrate Zoology Lecture 17: Phylum Arthropoda, Part 1

2. Lecture outline  Phylum Arthropoda  Diversity/Classification  Phylogeny  Bauplan Basics  Focus: Arthropod exoskeleton  Feeding/digestion  Circulation/gas exchange  Osmoregulation/excretion  Nervous system/sensory  Reproduction

3. Diversity/Classification  Subphylum Trilobitomorpha  Two longitudinal furrows divide body into three sections  Marine; Paleozoic  Extinct (end of Permian)

5. Diversity/Classification  Subphylum Crustacea: Lobsters, crabs, barnacles, copepods, etc…

6. Antarctic krill Euphausia superba

7. Subphylum Hexapoda: Insects Dennis Kunkel Brusca & Brusca

8. Subphylum Myriapoda: Centipedes and Millipedes

9. Subphylum Cheliceriformes Spiders, mites, horseshoe crabs, scorpions, sea spiders et al…

10. Phylogeny Based on body plan & development  Hypothesis 1:

11. Bauplan basics  Features shared with Phylum Annelida  Classic protostome development  Segmentation; segments added posteriorly  Nervous system architecture  Derived characters (differ from Annelida)  Rigid cuticle: contains chitin; forms exoskeleton  Open circulatory system; hemocoel  Reduced coelom  Key hypothesis: loss of functionality (i.e. peristalsis)  Where are coelom “remnants” located?

12. Intermediate phyla Why considered intermediate?  Phylum Onychophora  Phylum Tardigrada

13. Bauplan basics  Other features  Tagmatization  Paired jointed appendages  “Primitive condition”: appendages associated with each segment,  Lack motile cilia, except for some sperm  Why? Which other group has non-motile cilia?

14. Focus: cuticle  Epidermis  Secretes cuticle  Dermal glands  Variety of secretions  Sensory structures  Procuticle  Chitin  Calcium carbonate  Crustacea  Sclerotization  Joints  Epicuticle  Cement layer  Wax layer

15. Molting

16. Feeding/digestion  Different modes of feeding  Variety of mouthparts  Complete digestive system  Note digestive cecum

17. Circulation/gas exchange  Open circulatory system; ostiate heart  Hemocoel: space bounded by basement membrane of epidermis  Re-entry of hemolymph into heart?

18. Circulation/gas exchange  Respiration: Subphylum Crustacea  Gills; body surface (small forms)

19. Circulation/gas exchange  Respiration: Hexapoda & Myriapoda  Tracheal system (openings = spiracles)

20. Circulation/gas exchange  Respiration: Cheliceriformes  book lungs; book gills

21.  Crustacea:  Gills (ammonia release only  Antennal (green) gland  Entry via hemocoel channels & active transport  Selective secretion and uptake along tubule Osmoregulation & ammonia excretion

22.  Hexapoda, Myriapoda, Chelicerata:  Malpighian tubules  Closed distally: hemocoel  Active ion transport  fluid uptake  Open into hindgut  Adaptive value? Osmoregulation & ammonia excretion

23.  Organization  Brain (=cerebral ganglia)  Subesophogeal (subenteric) ganglion  Ventral nerve cord (paired, fused partly or completely)  Ganglia: one per segment or fewer (consolidated) Nervous system

24.  Crab: Note consolidated thoracic ganglia Nervous system

25. Sensory systems: Compound eye  Compound eyes comprised of multiple ommatidia  Interommatidial hairs in some…

26. Sensory systems: Compound eye  Key structures  Cornea  Crystalline cone/stalk  Iris (=corneal pigment cells)  Retinular cell w/rhabdome

27. Sensory systems: Compound eye  Light-adapted vs. dark-adapted eye  Shift in pigment position (within iris)  Alteration in light pathway  Consequences for sensitivity and acuity

28. Sensory systems: Compound eye  Mosaic theory of insect vision  Each ommatidium views piece of visual field  Adaptive advantages of compound eye  Acuity varies with  Ommatidia concentration  Size  Flatness  Key: angular distance

29. Sensory systems: Sensillae  Mechanosensory & chemosensory

30. Reproduction: Overview  Sexual reproduction  Usually gonochoristic  Some hermaphrodites  Example: Barnacles  Parthenogenesis in some groups  Part of aphid life cycle  Some crustaceans living in temporary ponds  Egg production often food limited. Why?  Example: Antarctic krill

31. Reproduction: Male system  Testes  Vas deferens  Seminal vesicle  Accessory glands  Types of secretions?  Ejaculatory duct  Gonopore  Spermatophores (in some)  Penis or modified appendages for copulation

32. Damselfly penis Barnacle penis Spider pedipalps

33. Reproduction: female system  Ovaries  Ovariole structure  Egg batches  Oviduct  Accessory glands  Types of secretions?  Copulatory bursa  Spermathecae  Function?  Bees and lobsters…

34. Reproduction & molting  Mate guarding  Adaptive value for male?  Adaptive value for female?

35. Reproduction & cannibalism  Hexapoda & Cheliceriformes (i.e. spiders)  Adaptive value for male?  Adaptive value for female?