Arthropod

1. Arthropod

2. Phylogeny of Arthropods Arthropoda Annelids (worms) Onychophorans (worms w/legs) Chelicerates (spiders) Crustaceans (lobsters) Insects (butterflies) Trilobites (extinct) Worm-like Ancestor

3. General Characteristics • metamerism (segmented body) • jointed appendages • bilateral symmetry • secreted exoskeleton • ecdysis (molting) • open circulatory system • ventral nerve cord and brain

4. DIVERSITY • Numbers • about 80% of all animals are arthropods • estimated to be over 30 million arthropods • far more of them than all other metazoan species combined • in virtually every conceivable environment: • marine, terrestrial, freshwater, and aerial habitats. Phylum Arthropoda Subphylum Trilobita (extinct) Subphylum Chelicerata Subphylum Crustacea Subphylum Uniramia (insects)

5. Chelicerata • comprises the xiphosurans (horseshoe crabs), arachnids, sea spiders • mostly terrestrial • cephalothorax-abdomen • 6 pairs cephalothoracic appendages • chelicerae, pedipalps, 4 pairs legs • no antennae

6. Subphylum Chelicerata • a. Xiphosura (horseshoe crab, Limulus polyphemus) • b. Arachnida • most chelicerates are arachnids • several taxa (orders), many are common and familiar • SCORPIONES (scorpions ) • ARANAE (spiders ) • OPILIONES (harvestmen, daddy longlegs ) • PSEUDOSCORPIONES (pseudoscorpions) • ACARINI (mites and ticks ) • c. Pycnogonida (the giant sea spider, • Colossendeis australis)

7. Limulus is a benthic scavenger and predator. • Prey include clams and other invertebrates that it digs for in the sand. • The tail spine is used as a self-righting mechanism if the animal is overturned accidentally. Lives up to 19 years • Reaches sexual maturity at about 9 to 12 years old Horseshoe Crab Limulus polyphemus, Carcinoscorpius rotunda, and Tachypleus gigas.

8. Horseshoe Crab • Mates during spring and summer full and new moons, onto ocean beaches. • Females lay up to 30 thousand eggs, which males fertilize before burying them in the sand • These eggs provide a major food source for migrating birds along the Atlantic coast. Those that are not eaten hatch during the next high tide, and the tiny larvae are carried away to sea.

9. Subphylum Crustacea • a heterogeneous taxon with many subtaxa • two pairs antennae • marine, freshwater, and terrestrial • Primarily aquatic • Free-floating larval stage • 26,000+ known species

10. Subphylum Crustacea • ANOSTRACA • fairy shrimp and brine shrimp • PHYLLOPODA • tadpole shrimps, ostracod, water fleas • MALACOSTRACA • the largest, most heterogeneous, and diverse crustacean taxon • shrimps, crabs, lobsters, mantis shrimps, pillbugs, crayfishes • COPEPODA • copepods • enormous ecological importance as planktonic herbivores • CIRRIPEDIA • barnacles

11. Respiration • Gills • a. General • gills are evaginations • typical of aquatic animals • blood is oxygenated by gills • oxygen delivered to tissues by blood • b. Crustacean Gills • crustacean gills are usually associated with appendages • blood circulates through the gill and is oxygenated • c. Book Lungs • present in many arachnid orders • similar to book gills of horseshoe crabs • oxygen transport from the lungs to the tissues is by blood

12. Closed Circulatory System Open Circulatory System

13. NERVOUS SYSTEM • 1. General • nervous system is adapted for the needs of a segmented animal as is that of annelids • annelid and arthropod nervous systems are similar • the similarities may be convergent • 2. Arthropod Ground Plan • ladder like nervous system • dorsal brain in the head • a pair of circumenteric connectives that encircle the gut • a paired, ventral, longitudinal nerve cord • paired segmental ganglia • transverse commissures between ganglia • longitudinal connectives • segmental sensory and motor nerves

14. NERVOUS SYSTEM Side view of body showing relative position of circulatory (yellow), digestive (green), and nervous (blue) systems.

15. SENSE ORGANS • 1. General • receptors for light, vibrations, chemicals, equilibrium, gravity • cuticle modified to form a vast array of receptors (sensilla) • 2. Sensilla • specialized for various environmental events • consist of: • <>modified cuticle, usually a seta • <> a modified cilium • <> sensory neurons • <> support cells

16. SENSE ORGANS • 3. Mechanoreceptors • a. Trichobothria • extremely sensitive mechanoreceptors detect weak, low velocity air currents • a long, slender, solid seta • especially common and important in arachnids • a blinded spider can capture flies using its trichobothria • 4. Chemoreceptors • detect chemicals • modified hollow setae with substrate-specific chemosensory neurons • chemoreceptive sensilla resemble mechanoreceptive setae

17. SENSE ORGANS • 5. Equilibrium and Gravity • a. Statocysts • several malacostracan crustaceans have statocysts • analogous to the vestibule of the vertebrate inner ear • detects gravitational field and acceleration • 6. Tympanal Organs • some arthropods can hear, i.e. detect vibrations in air • tympanal organs are present in several insect groups • cicadas, crickets, grasshoppers, moths • a thin sheet of cuticle (eardrum) over an opening

18. SENSE ORGANS • 7. Hygroreceptors • humidity receptors • very important to terrestrial arthropods • 8. Photoreceptors • a. General • widespread, often well-developed and sophisticated • two types: • <>"median" pigment-cup ocelli • <>"lateral" compound eyes • <>both often present in the same individual

19. SENSE ORGANS • 2. Pigment-cup Ocelli • a. General • highly variable within the arthropods • all the receptor units (retina cells) share • a common lens • b. Structure • a cup-shaped layer of pigment-containing cells • encloses a cup-shaped layer of photoreceptor cells known as the retina • concavity of the cup is oriented toward the light source • pigment layer prevents the entry of light from any other direction • a cuticular lens (cornea) usually present

20. SENSE ORGANS • 3. Compound Eyes • General • multiplelight receiving units, known as ommatidia • each ommatidium usually has its own lens (or cornea) • most have one pair • b. Ommatidia • ommatidium is the individual, self-contained, independent light-detecting unit • 15-several thousand in a single compound eye • each includes • >focusing system (cuticular cornea and crystalline cone) • light-transmitting structure (cone stalk) • >light sensitive cells • >screening pigment to isolate (pigment cells)

21. Compound Eye Lens Crystalline cone Pigment cells Facet Visual cells Nerve fibers from visual cells Optic nerve Ommatidia

22. REPRODUCTION • 1. General • most arthropods are gonochoric • fertilization may be external or internal in aquatic arthropods • always internal in terrestrial species • 2. Sperm Transfer • sperm transfer usually by mating or copulation • females usually store the sperm in a seminal receptacle

23. 3. Spermatophores • a. General • many arthropods transfer sperm in packets • an adaptation for sperm transfer on land • male abandons spermatophore for female to find or may place it in the female gonopore • most insects use copulation • 4. Copulation • present in many aquatic arthropods (crustaceans), also in derived terrestrial forms • often with courtship and behavior patterns • anatomical equipment for internal fertilization by copulation • male inserts an intromittent organ into the reproductive tract of the female • deposits sperm or spermatophores into her seminal receptacle

24. Arthropod Development Zoea Nauplius Megalops

25. Symbiosis

26. Camouflage Decorator Crab Sponge crab

27. Camouflage: anemone crab

28. coral guard crabs and pocilloporid corals

29. gall crabs and pocilloporid corals

30. scarlet cleaner shrimp

31. sea cucumber crab and sea cucumbers

32. pompom crabs and sea anemones

33. crabs and sea anemones