Phylum Arthropoda :

1. Phylum Arthropoda: Blueprint for Success Chapter 14 and 15

2. Characteristics of Arthropods • Modified segmentation – body regions specialized for specific functions (tagmatization). • Chitinous exoskeleton used for support and protection • Paired, jointed appendages • Growth accompanied by molting (ecdysis)

3. Characteristics of Arthropods • Ventral nervous system • Reduced coelom • Open circulatory system where blood is released into tissue spaces (hemocoel) • Complete digestive tract • Metamorphosis often present

4. Arthropods • Successful in almost all habitats on the earth. • Most abundant animals – Several million species identified • 30 to 50 million species may yet be undescribed • Triploblastic, protostome development • Exhibit bilateral symmetry • Four aspects contribute to arthropod success. • 1. Metamerism • 2. Exoskeleton • 3. The Hemocoel • 4. Metamorphosis

5. Metamerism • Segmentation, most evident externally • Each external segment bears a pair of appendages • Body cavity not divided internally • Permits the specialization of regions of the body for specific functions • Regional specialization = Tagmatization • Body regions (tagmata) specialized for: feeding, sensory perception, locomotion, visceral functions.

6. The Exoskeleton • External, jointed skeleton which encloses arthropods • Provides support, protection, and prevents water loss • System of levers for muscle attachment and movement • Secreted by epidermal cells • Epidermis covered by exoskeleton on outside • Consists of two layers: • 1. Epicuticle = outermost, waxy lipoprotein layer • 2. Procuticle/Endocuticle = bulky inner layer made of chitin

7. The Exoskeleton • Hardening of the procuticle provides armor-like protection • Modifications of the exoskeleton • Formation of joints • Sensory receptors (bristles, lenses, etc) • Gas exchange • Must be periodically shed for growth (ecdysis)

8. The Exoskeleton • Epicuticle and Procuticle: epicuticle exocuticle procuticle endocuticle epidermis

9. The Hemocoel • Provides an internal cavity for the open circulatory system of arthropods • Allows for the exchange of nutrients, wastes, and (sometimes) gases

10. Metamorphosis • Indirect development, a significant change in physiology as the immature form becomes an adult • Reduces competition between adults and immature stages

11. Metamorphosis • Evolution of arthropods has resulted in an increasing divergence of body forms, behaviors, and habitats between immature and adult stages. • Ex: Larval crabs feed on plankton, adult crabs prowl sandy bottoms for live prey. • Ex: Caterpillar feeds on leafy vegetables, adult butterfly feeds on nectar from flowers.

12. Subphylum Crustacea • Examples: • Crayfish, crabs, lobster, shrimp, barnacles and copepods. • Two unique characteristics: • 1. Two pairs of antennae • 2. Biramous appendages • Five classes of crustaceans and numerous orders • Class Malacostraca** • Class Maxillopoda** • Class Branchiopoda • Class Remipedia • Class Cephalocarida

13. Class Malacostraca • “Soft Shell” • Largest class of crustaceans: • crabs, lobsters, crayfish, shrimp, krill, isopods • Body divided into two regions • 1. Cephalothorax (fusion of sensory/feeding and locomotion tagmata) • 2. Abdomen (a muscular tail)

14. Class Malacostraca • Paired, biramous appendages in both body regions • Appendages on Cephalothorax: • Pairs 1 and 2 – Antennae (TWO pairs!) • Pairs 3 through 5 – Mouth appendages • Mandible Pair (Chewing) • Maxillae (Food handling) • Pairs 6 through 8 – Maxillipeds • Accessory sensory and food handling appendages • Pairs 9 through 13 – Pereopods (Walking legs) • Cheliped (Pincher-like) • Appendages on Abdomen • Pleopods (Swimmerets) • Telson used

15. Class Malacostraca

16. Class Malacostraca Reproduction • All crustaceans are dioecious • Mating occurs after molting of the female • In females, developing eggs attach to pleopods and are brooded until hatached • In males, pleopods are modified into claspers and used for sperm transfer • Crayfish have direct development

17. Class Malacostraca Feeding Predators, herbivores, scavengers Foregut includes an enlarged stomach, specialized for grinding Midgut = “intestine” Short hindgut ends in anus and used for water and salt regulation

18. Class Malacostraca Gas Exchange & Circulation Sensory & Regulation Ventral nervous system Compound eyes Crayfish: Excretion organs are called “green glands” Other crustaceans: maxillary glands • Gills in gill chamber • Between the carapace and body wall • Muscular Heart • Dorsal, anterior, and posterior arteries empty into sinuses of hemocoel

19. Class Maxillopoda • Includes Barnacles and Copepods • Copepods are most abundant crustacean • Marine and Freshwater • Barnacles are sessile • Marine only • Most monoecious • Attach to various substrates • Some are parasitic

20. Subphylum Hexapoda • Most successful land animals in terms of numbers of species and individuals • Bodies divided into three tagmata • Five pairs of head appendages • Three pairs of legs on thorax

21. Class Insecta • 30 Orders within Class Insecta! • Adult Generalized Insect Characterized by: • Body divided into head, thorax, abdomen • Three pairs of legs • Two pairs of wings

22. Class Insecta Body Plan • Head • Single pair of antennae • Mouthparts • Compound eyes • 0 to 3 ocelli (simple eyes) • Thorax • Three segments: prothorax, mesothorax, metathorax • One pair of legs attaches to each thoracic segment • Pair of wings attach at margin between mesothorax and metathorax • Abdomen • 10 to 11 abdominal segments

23. Insect Flight • Insects utilize many forms of locomotion: walk, run, jump, swim, but flight is perhaps the most important • Insects were the first animals to fly • Important from an evolutionary perspective! • Wings most likely evolved from outgrowths of the thorax which protects the legs • Required thermoregulation • Some insects use a synchronous (direct) flight mechanism which others use an asynchronous (indirect) flight mechanism.

24. Insect Flight • Synchronous (Direct) Flight • Used by butterflies, dragonflies, and grasshoppers. • Flight muscles act on wing bases • A single nerve impulse in flight muscles results in a single wing cycle • Asynchronous (Indirect) Flight: • Used by flies and wasps • Flight muscles act on body wall • Changes in shape of the thorax cause wing movements. • A single nerve impulse results in many cycles of the wings

25. Insect Feeding • Variations in mouthparts include specializations for sucking or siphoning plant or animal fluids • Mouthparts: • Labrum- upper liplike structure, sensory and not derived from paired appendages • Mandibles- chewing mouthparts • Maxillae- have cutting surfaces and a sensory palp • Labium-sensory lower lip • All aid in food handling

26. Insect Digestive System • Long and straight and consists of the foregut, midgut, and a hindgut. • Foregut • Behind pharynx is a crop that is used for storage • Proventriuculus or gizzard moves food to midgut helps grind • Midgut • Aids in digestion and absorption • Gastric cecae increase surface area • Hindgut • Primarily involved with reabsorption of water

27. Insect Gas Exchange • Gas exchange with air requires a large surface area for the diffusion of gases • Accomplished through highly branched systems of chitin-lined tubes called tracheae • Tracheae open to outside of body through spiracles • Spiracles can close to prevent water loss • Most insects have ventilating mechanisms • Moves air into and out of tracheal system • Contracting flight muscles • Passive suction (vacuum) draws air in • Abdominal muscle contraction (pump)

28. Insect Circulation • Open circulatory system similar to other arthropods but blood vessels less well developed • Blood carries nutrients, hormones, wastes • Blood is not important in gas exchange • Most insects are ectotherms, but some generate heat using flight muscles

29. Insect Sensory Functions • Ganglion in head region • Sense organs specialized for functioning on land • Insects are capable of some learning have a memory • Bees recognize flowerlike objects • When bees are rewarded with nectar, they will choose flowers with that same odor in subsequent trials • Capable of detecting light • Used in orientation, navigation, feeding, etc • Compound eyes are well developed in adults