Arthropods Characteristics

Arthropods-Insects Makes up ¾’s of all animals species Includes insects, spiders, scorpions, millipedes, centipedes, crabs, lobsters & crayfish Anthropod means “jointed foot/leg” Jointed appendages (legs, antenna, mouth parts) Segmented body with paired appendages on each segment

Arthropods Millipedes & Centipedes

Arthropods-Spiders 6. External exoskeleton made of chitin (carbohydrate) & protein for protection & support 7. Exoskeleton has 3 layers- outer waxy layer repels water, middle layer has calcium for extra strength & inner layer has flexible joints for movement 8. Deuterostomes 9. Coelomate 10. Ventral nervous system

Arthropods-Crabs & Barnacles

Arthropods-Scorpions 11. Open circulatory system 12. Specialized sensory receptors & high degree of cephalization 13. Have simple or compound eyes & segmented antenna

Arthropods-Lobsters & Crayfish

Arthropods Movement & growth

Arthropods-Horseshoe crabs 1. Muscles occur in bundles & are attached to inside of exoskeleton on each side of joints

Arthropod-Growth 2. Exoskeleton must be periodically molted (shed) for organism to grow 3. Molting called ecdysis 4. Molting hormone released & causes epidermal cells to secrete enzymes that digest & loosen inner exoskeleton 5. New exoskeleton secreted by epidermal cells flexible at first & must harden so arthropod not vulnerable to predators so often stay in hiding after molting 6. Arthropods go through numerous molts

Arthropods Evolution & Taxonomy

Arthropods Four subphyla Trilobita- extinct trilobites Crustacea- shrimps, lobsters, crayfish & barnacles Chelicerata- spiders, scorpions & ticks Uniramia- centipedes, millipedes & insects

Arthropods Subphyla trilobita Includes extinct trilobite Marine Have a head & segmented trunk with one pair of legs one each segment Breathe through gills Single pair of antenna

Subphylum Chelicerata  Characteristics 1.Includes 2 classes- Xiphosura (horseshoe crab) and Arachnida (spiders, ticks, scorpions & mites) 2. Have a cephalothorax (fused head & thorax) and abdomen

Subphylum Chelicerata  Characteristics 8. Ticks & Mites a. Parasitic arachnid b. Need blood meal to molt c. Ticks carry Lyme disease & Rocky Mountain Spotted Fever 9. Scorpions a. Prefer dry regions b. Breath through book lungs c. Nocturnal predators

Subphylum Crustacea Characteristics 1.Marine members include shrimp, lobster, copepods, barnacles & crabs 2. Terrestrial crustaceans called isopods includes pillbugs & sowbugs 3. Freshwater members include crayfish & Daphnia (water fleas) 4. All have jaws or mandibles for chewing or tearing 5. have 10 pairs of jointed appendages 6. Breathe through gills 7. Barnacles a. Marine b. Sessile crustaceans that live in limestone case c. Filter plankton with 12 appendages called cirri 8. Isopods (pillbugs & sowbugs) a. Some live on land in dark places

Subphylum Crustacea 9. Crayfish a. Antennules located on head help balance, touch & taste b. Statocysts- balancing organs at the base of antennules c. Maxille- paired mouthparts that move side to side to tear food d. Maxillipeds- help hold food e. Swimmerets- under abdomen to swim, gas exchange, & protect eggs/ young f. Abdomen ends in flat segment called telson with flat uropods on each side g. Chitinous teeth in stomach grind food h. Open circulatory system with heart to pump blood to gills & body cells i. Gills attached to walking legs

Subphylum Crustacea Copepods a. Largest group of crustaceans b. Make up most of the marine plankton c. Serve as food for many marine animals d. Found in freshwater, marine & moist terrestrial environments

Subphylum Uniramia Characterists Class Chilopoda Class Diplopoda 1.Includes 3 classes- Chilopoda (centipedes), Diplopoda (millipedes) & Insecta 2. Most are terrestrial 3. Exoskeleton prevents desiccation (water loss) Class Chilopoda 1.Terrestrail centipedes – VS (not) 2. Have 1 pair of legs per body segment Class Diplopoda 1.Terrestrial millipedes 2. Roll into balls when threatened & spray noxious chemical containing cyanide

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The head and thorax are covered by a common “shell,” or covering termed the “carapace.” The front end of the carapace has “the rostrum,” a spike-like projection from the front end. The eyes are on stalks and there are two sets of sensory appendages termed antennae. Each of the first pair of antennae has two branches. Each of the second pair of antennae has one long branch and a smaller scale-like branch at the base. The primitive forms have eight thoracic segments.

Each thoracic segment bears an appendage that may be used for walking. Each thoracic appendage may bear a gill found up under and protected by the carapace. The abdomen projects beyond the carapace and has six segments. The first five abdominal segments have flap-like swimming appendages found underneath it. The last abdominal segment bears a pair of lateral flaps and is typically flattened.  Together with the lateral flaps, it is often called the tail fan.

True Crabs Crabs are flattened from top to bottom. The first pair of remaining thoracic appendages ends in large pinching claws. The last four pairs of thoracic appendages are walking legs. The first abdominal segment is small. The abdominal appendages are small and modified, and not used for swimming. The abdomen is curved under the thorax where it fits in a groove on the animal's underside. True Crabs

Arthropods of the PNW

Barnacles

Barnacles Acorn barnacle White acorn barnacle Leaf barnacle

True Crabs Dungeness crab (Shield-backed) Kelp crab Purple shore crab

True Crabs Red crab Oregon cancer crab

Other “Crabs” Hairy hermit crab Pacific mole crab

Shrimp Broken (Stiletto)back shrimp

Isopods & Amphipods Vosnesensky’s isopod Sand flea

Sea Spiders Stearns’ sea spider

Sea Spiders

Sea Spiders

Sea Spiders

Phylum Arthropoda Class: Merostomata--horeshoe crabs Class: Pycnogonida--sea spiders Class Crustacea: Subclass: Branchiopoda--fairy shrimp, brine shrimp (2) Subclass: Copepoda—copepods (3) Subclass: Cirripedia—barnacles (4) Subclass: Malacostaca: Order: Stomatopoda--mantis shrimp Order: Euphausiacea—krill Order: Decapoda--shrimps, lobsters, crabs

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