Arthropoda Classification Arthropods Adapted to aquatic and terrestrial

Arthropoda

Classification

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

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

Exoskeleton • Composition – 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 – Ommatidia • • 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 – 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 – Leading edge faces up • Downstroke – Leading edge faces down

Flight Muscle Control • Synchronous – 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 – 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