Arthropoda

Classification

Arthropods Adapted to aquatic and terrestrial environments Probably first animals on land and in air Most diverse animal phylum

Segmentation Pair of appendages per segment Fused segments – tagmata Reduced number for most arthropods Specialized – locomotion, feeding, defense… Fused segments – tagmata Head, thorax, abdomen

Exoskeleton Composition Advantages Chitin – cross-linked polysaccharides Protein and lipids Calcium salts – very hard Advantages Protection Muscle attachment Joints Wings

Exoskeleton – Laminated Structure Epicuticle Protein and lipids Procuticle Exocuticle Secreted before molt Endocuticle Secreted after molt

Ecdysis

Respiration Terrestrial – trachea (network of breathing tubes) Aquatic – gills High oxygenation = high metabolic rate

Sense Organs Compound eye Antennae Ommatidia Tactile, chemosensitive Photoreceptors Lens Pigment cells Nerve fiber Antennae Tactile, chemosensitive

Compound Eye

Subphylum Chelicerata No mandibles – mostly suck food Two tagmata Cephalothorax Abdomen Six pairs of appendages 1 pair chelicera 1 pair pedipalp 4 pair walking legs

Class Merostomata Limulus Horseshoe crab Unsegmented carapase Book gills Spike-like telson

Class Arachnida Spiders, mites, scorpions, ticks Terrestrial and marine Chelicera often develop into fangs or pincers Most feed by sucking fluid from prey or host Specialized organs Excretory system - Malpighian tubles Allows conservation of water Book lungs or book gills

Order Araneae Spiders Poison gland Digestive enzymes injected into prey Malphigian tubules 4 pairs of simple eyes Sensory setae

Araneae Anatomy

Reproduction Dioecious – male and female Eggs laid in silk cocoon

Web Silk Silk glands at posterior end Made of protein Solidifies when it hits the air Very strong Silk glands at posterior end Spinnerets – help manipulate the growing silk strand

Subphylum Crustacea Mostly aquatic 2 Antennae, maxillae and mandible Biramous appendages Chelipeds – often enlarged to form claws

Crustacean Body Plan

Uniramia Key Features Legs do not branch Specialized feeding mandibles Tracheal system of gas exchange Malpighian tubules Single pair of antennae

Uniramia Classes Diplopoda Millipedes Chilopoda Centipedes Insecta

Diplopoda Fused segments Two pairs legs per segment Eat vegetable matter

Chilopoda Pair of legs per segment Predator Poisons prey

Insecta Over one million species Found all over the world Not found in marine environment – dominated by crustaceans Structural Features Tagmata – head, thorax, abdomen Legs only from thorax Wings

Insect Flight Muscles

Figure-8 Pattern Upstroke Downstroke Leading edge faces up Leading edge faces down

Flight Muscle Control Synchronous Asynchronous One impulse = one stroke Dragonflies, butterflies Asynchronous One impulse = multiple strokes Flies, bees, midges

Basic Anatomy

Respiration and Circulation Tracheae Network of tubules Open to outside – Spiracles Branch into fine tracheoles Supported by bands of chitin Open circulatory system Haemocoel filled with haemolymph

Digestive System Foregut Midgut Hindgut Mouth, esophagus, crop, gizzard Grinding and storage Midgut Stomach and gastric ceca (increases surface area) Digestion and most absorption Hindgut Intestine, rectum, anus

Excretion Malpighian Tubules Extensions off of the intestine Project into the haemocoel Exchanges waste with haemolymph

Metamorphosis Holometabolous Complete – example: butterfly Egg  Larva  Pupa  Adult Many larval tissues disintegrate during pupa stage

Metamorphosis Hemimetabolous Partial – example: roach Egg  Nymphs  Adult Nymphs are similar to adults