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Arthropods and Their Relatives
• Characteristics
– Exoskeleton (external covering made of CHITIN)– Molts or sheds exoskeleton to grow
– Jointed appendages - Groups very often named in relation to number or type of feet.
– Tend to undergo metamorphosis or pass through a number of distinct growth stages during their lives
– Tendency toward High degree of cephalization, especially in Class Insecta
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Arthropods• Relative abundance.
– 3/4 of all known species of animals are arthropods.
– More known species of arthropods than known species of plants and animals combined. Great diversity in form and habitat.
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Major Groups of Arthropods
• Subphylum Trilobita - all forms extinct (believed) perhaps some of earliest arthropods
• Subphylum Chelicerata - First pair of appendages form chelicera or pincher-like structures used for feeding. 4 pair of walking legs, no antennae. The Arachnida is the only important parasitic group.
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Major Groups of Arthropods
• Subphylum Crustacea - mostly aquatic, most have gills, two pair of antennae. Biramous appendages, meaning limbs have more than one branch. Also have mandibles. Some are parasitic but we will not cover them.
• Subphylum Uriramia – single branch or uriramous appendages, mandibles, one pair of antennae
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Major Groups of Arthropods
• Diplopoda - Millipedes - two pair of legs per body segment
• Chilopoda - Centipedes - one pair of legs per body segment
• Insecta - 3 pair of legs on adults, many with wings, most important group
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Metamorphosis• Simple or gradual
– three changes• egg• nymph
– 3-5 instars
• adult
– adults and nymphs • eat same food
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Metamorphosis• Complex or complete
– four changes• egg• larva• pupa• adult
– larvae and adults• eat different food
– larvae are destructive
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Fundamental External structure
• Insects– 3 body regions
• head• thorax• abdomen
– 3 pair legs attached to thorax– 1 pair antennae– wings usually present in adult state.
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Fore WingHind WingAntennae
Jumping Leg
Cerci
OvipositorSpiracles Walking Legs
Palps
Mouth
Simple Eye
Compound Eye
Abdomen HeadThorax
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Circulatory System• Closed circulatory system• Well developed heart pumps blood• Heart is long and narrow• Arteries branch into blood vessels
and return blood to the heart via veins – cool, just like us!
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Excretion• Recall the Nephridia in Annelids
• The Malphigian Tubules in Arthropods collect nitrogenous wastes in the tubules from blood
• Wastes are concentrated (like a kidney does.) Why concentrated?
• Excreted out anus
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Book Gills – folded Gills increase SA for Respiration
Horseshoe Crab
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Respiratory System
• Gills or lungs, as you’ll see on the next slide
• Organism is too large to rely on surface area. That is, the internal volume is too great to be supplied with oxygen from a minimal SA.
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Book Lungs are Characteristic of Arachnids
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Sensory Adaptations
• Well developed nervous system
• Compound eyes with many lenses give Mosaic Vision or multi-images
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Ultravision – Seeing in the UV Spectrum
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The Compound Eye
Each crystalline eye generates an image. All
images together generate a mosaic effect
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Simple Eye (Ocelli)• Do not form the picture• Just gather light• Tell whether it’s light or dark
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Exoskeleton of Chitin and
Muscles attach on
Inside
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How do You Grow Larger if you Skeleton is on the
Outside?
Molt, or shed the
outer covering
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External structure of Subphylum Chelicerata, Class Arachnae
• Chelicerates have specialized mouthparts called chelicerae – think of the hooked grabbers!
• Arachnids (spiders and mites)– 2 body regions
• Cephalothorax• abdomen
– usually 4 pair legs – no wings– no antennae
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Chelicera = Fangs, for example, on a Spider
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Chelicerates Include the Horseshoe Crab
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Body of ArachnidsThe Spider Body
A spider's body is divided into two parts:
Cephalothorax - Fused head & thorax. The legs are locatedon the cephalothorax
Abdomen - Similar to that of insects..
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Other Members of Phylum Arachnida (4 Pairs of Walking
Legs)
1. Spiders2. Ticks and Mites3. Scorpions
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Nature Says Don’t Bug Me with the Colour Red!
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How Nature Says Do Not Touch