Phylum Arthopoda - Arthropods includes spiders, scorpions, horseshoe crabs, centipedes, crustaceans, insects The largest and most diverse animal

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1 Phylum Arthopoda - Arthropods includes spiders, scorpions, horseshoe crabs, centipedes, crustaceans, insects The largest and most diverse animal phylum.

2 Almost 2/3 of all species that have been described are arthropods There may be as many as 30,000,000 species of insects alone Abundant in all habitats, but dominate terrestrial regions Most arthropods are small, but a few may be as large as 3.6 m Economically important, especially insects Pollinate crops, control insects and weeds Many species are eaten - especially crustaceans Compete with humans for food Cause extensive damage to food crops Spread diseases

3 Key Innovations of Arthropods: Jointed appendages, complete exoskeleton, segmental body with specialization of body regions Arthropod means "jointed feet" Jointed appendages are specialized for different functions: legs, mouthparts, antennae Joints in appendages make them highly functional for walking, and grasping Antennae are sensory - sounds and chemicals Mouth parts specialized for different food sources

4 Rigid exoskeleton, made of chitin and protein helps to protect against predators and reduces water loss - allows life in dry environments Skeleton functions as attachment for muscles muscles attach to interior of skeleton Exoskeleton limits arthropods maximum size although chitin is tough, it is brittle and cannot support great weight without increasing its thickness greatly Exoskeleton must be shed in order for increase in size - ecdysis

5 Segmental body plan clear in all forms, but segments often fused to form specialized body regions - tagmats Insect: head, thorax, abdomen Crustacean: cephalothorax, abdomen

6 Living arthropods divided into three subphyla - based on appendages Chelicerata: first appendages are for feeding - chelicerae - fangs of spiders feeding appendages of horseshoe crabs Crustacea and Uniramia (Tracheata) together called the Mandibulates: first appendages are antennae, first feeding appendages are called mandibles

7 Mandibulates are divided into two subphyla - Crustaceans and Uniramians (Tracheata) - based on appendages Crustaceans have biramous (branched) appendages Uniramians (insects, millipedes, centipedes) have uniramous (unbranched) appendages

8 General Biology of Arthropods Exoskeleton All arthropods covered by hardened exoskeleton made of chitin and protein - secreted by and fused with epidermis varies in toughness and thickness many crustaceans add calcium carbonate - increases rigidity Functions of exoskeleton prevents excessive water loss protects from predators and injury Molting - a liability of the exoskeleton Growth requires periodic ecdysis, shedding of outer cuticle New exoskeleton grows beneath old one Separated by a fluid that dissolves components of old skeleton Old skeleton cracks open and is shed New skeleton is soft and must be expanded to full size Hardens with exposure to air or water

9 A new exoskeleton forms inside old - old one must be shed - ecdysis The new exoskeleton and all of the body parts it encloses must be pulled out of old exoskeleton - includes legs, claws, gills, etc. Each new life stage is called an instar

10 Eyes Ocelli are simple eyes with single lenses Sometimes occur together with compound eyes Function in distinguishing light and dark Compound eyes Composed of many ommatidia - independent units Each covered with a lens - contains eight retinular cells and central light-sensitive rhabdom Each ommatidium receives its own image and is connected to a nerve cell - entire image is integrated in the brain

11 Gut is tubular and extends from mouth to anus - with specialized regions - crop, stomach (midgut), hindgut, intestine, rectum Circulatory System is open heart extends through thorax and abdomen contraction sends blood forward relaxation draws blood from tissues one-way valves in heart allows blood to flow forward only blood from anterior end flows through tissues to posterior end

12 Respiratory System Crustaceans have feathery gills under carapace Chelicerates have book gills and book lungs - series of plates with thin respiratory epithelium

13 Terrestrial Uniramians and some Chelicerates have trachaea Trachea are branched tubules that allow air to diffuse into the body smaller tracheoles bring air to individual cells air entry controlled through external spiracles closing spiracles conserves water flow is mostly passive - muscular movements can increase flow limits body size because all cells must be able receive oxygen

14 Excretory System Several forms of excretory systems Terrestrial Uniramians have Malpighian tubules Slender tubular projections off the digestive tract at the junction of the midgut and hindgut Water and solutes pass through walls of tubules nitrogenous wastes are precipitated as uric acid or guanine Fluid with waste is emptied into hindgut and eliminated Most water and valuable solutes reabsorbed by hindgut An efficient system that conserves water - a good adaptation for terrestrial life

15 Nervous System Double chain of ganglia runs along ventral surface Three fused pairs of dorsal ganglia form the brain ventral ganglia control local activity of body regions many activities continue with brain removed Brain appears to be inhibitor, not stimulator (as in vertebrates) some activities begin spontaneously when head is removed

16 Three Classes of Chelicerates Class Arachnida - spiders, scorpions, ticks Class Merostomata - horseshoe crabs Class Pycnogonida - sea spiders

17 Class Arachnida - Arachnids Largest class of chelicerates includes spiders, daddy longlegs, scorpions, mites & ticks All have a pair of chelicerae, pair of pedipalps, four pairs of legs Chelicerae are first appendages, fangs with poison glands Pedipalps are next, similar to legs - rarely used for locomotion often used for catching and handling prey may also chew with basal portion may function as copulatory organs or sensory organs scorpion pincers are pedipalps Most are carnivorous, some mites are herbivorous Most ingest only liquified foods, digestion begins externally Most are terrestrial, direct transfer of sperm for reproduction Respire with trachea, book lungs or both

18 Class Merostomata - Horseshoe Crabs Example: Limulus, common on North Atlantic coasts Ancient group, Limulus fossils date to 220 million years old Live in deep water, migrate to shallow coastal waters to mate Feed at night on mollusks and annelids Shell-like carapace over cephalothorax protects most body parts Swim with carapace down moving abdominal plates Possess four pairs of walking legs, chelicerae, and pedipalps Respire via five pairs of book gills

19 Class Pycnogonida - Sea Spiders Common in marine habitats, especially in cool waters rarely observed because of small size Not closely related to spiders Adults are parasites or predators on other animals Have sucking proboscis with terminal mouth Body consists mostly of cephalothorax, no well-defined head Possess four to six pairs of legs Males exhibit parental care of young, carry eggs on legs

20 Subphylum Crustacea - Crustaceans includes shrimp, crabs, crawfish, lobsters, pillbugs, copepods, brine shrimp, barnacles have biramous (two branch) appendages, two pairs of antennae, and 3 pairs of feeding appendages, larger forms have feathery gills near base of legs Most have a nauplius larva

21 Have legs on thorax and abdomen like millipedes and centipedes but unlike insects Having two pairs of antennae is unique to crustaceans Many have compound eyes Have tactile (touch sensitive) hairs over whole body Excretion of nitrogen wastes occurs mostly across surface of cuticle Variety of sexual styles and care of young

22 Crustacean Diversity Decapod ("ten-footed") Crustaceans - includes lobsters, shrimp, crabs, crawfish Exoskeleton reinforced with calcium carbonate Anterior segments fused into cephalothorax, covered by carapace Crushing pincers common, used to obtain food and in defense Swimmerets used in reproduction and locomotion Snapping of telson and uropods causes forceful, rapid movement to the rear

23 Crustaceans Diversity Terrestrial forms - pillbugs, sowbugs, isopods Amphipods are both terrestrial and aquatic Planktonic crustaceans Copepods (Copepoda) Water fleas (Cladocera) Ostracods (Ostracoda) Fairy shrimp and brine shrimp (Anostracoda) Sessile Crustaceans Include barnacles (Cirripedia) Sessile adults, free-swimming larvae Head attaches to substrate, food swept into mouth by feathery legs have shell-like plates covering body

24 Subphylum Uniramia (or Tracheata) - has three classes Class Chilopoda - centipedes Class Diplopoda - millipedes Class Insecta - insects Well adapted to terrestrial life Respire with trachea Malpighian tubules for excretion Waxy cuticle on exoskeleton

25 Centipedes and Millipedes - both have head tagmat followed by numerous repeating segments - each with paired appendages Centipedes (hundred legs) have one pair of legs per segment Millipedes (thousand legs) have two pairs of legs per segment Centipedes - carnivorous, most eat insects Appendages of first body segment are poisonous fangs Millipedes - most are herbivorous Can roll bodies into a flat coil May secrete defensive fluids and cyanide gas Reproduction similar in both groups Sexes separate, fertilization is internal, copulate to transfer sperm, all species lay eggs Juveniles are similar to adults in appearance

26 Class Insecta - Insects Largest group of organisms on earth - with great diversity Especially numerous in the tropics

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29 Most are terrestrial but many are aquatic in freshwater Have three body segments: Head, thorax, abdomen Have three pairs of legs, all attached to thorax Have one pair of antennae May have one or two pairs of wings Sexes separate with internal fertilization Wings arise as sack-like outgrowths Wings are solid except for veins Wings are not homologous to other appendages

30 Digestive tract is tubular and slightly coiled digestion occurs within stomach or midgut Excretion by Malpighian tubules Respiration via trachea that extend throughout body may have air sacs with muscles that create a bellows system to allow deeper air circulation in body Spiracles can be closed by muscles to retard water loss

31 Possess wide variety of sensory systems - in addition to eyes Sensory hairs located all over bodies especially on legs and antennae Sounds detected by tympanum Sensory hairs may also detect sound waves Produce sounds which may inaudible to humans Chemicals (pheromones) are also used to communicate

32 Development Most insects hatch from laid eggs - rarely develop within mother After hatching young insects undergo regular ecdysis through a series of instars Often the larva is very different from the adult and undergoes metamorphosis to become adult In simple metamorphosis, wings develop during juvenile stage there is no "resting stage" before last molt Immature stages are called nymphs Seen in beetles, grasshoppers, dragonflies, cockroaches, silverfish Simple Metamorphosis

33 In complete metamorphosis, wings develop during a resting stage just prior to final molt resting stage called a pupa or chrysalis - at this time cellular reorganization occurs to form adult body Pupa does not normally move, except in mosquitoes Complete Metamorphosis Juveniles and adults live in distinct habitats - larvae often worm-like, lacking large eyes, and legs Larvae usually have chewing mouth-parts, even if adults have sucking mouth-parts Pupae are usually inactive and do not feed seen in moths, butterflies, beetles, bees, wasps, ants, flies, fleas