30.5 Arthropods

Overview Phylum Arthropoda +1 million species Are protostomes and coelomates

Body Structure Freely movable jointed appendages Exoskeleton made of chitin Protection, muscle attachment, locomotion, prevention of dessication

Molting: shedding of exoskeleton Body secretes new/larger exoskeleton Starts off soft/wrinkled, then hardens Segmented, but some fused into regions Head, thorax, cephalothorax, abdomen Appendages specialized for function Reproduction, eating, sensory reception

Nervous System Well-developed nervous system Sense organs Brain and ventral solid nerve cord Sense organs Antennae 2 types of eyes (simple and compound)

Compound Eye Made of several visual units (operate independently) Focuses image --> results in eye sight that's good for tracking movement

Crustaceans

Habitat Marine Barnacles, shrimps, crabs, lobsters Freshwater Crayfish Terrestrial Sow bug (roly poly bug)

Body Structure Exoskeleton Head generally has 1 pair of compound eyes and 5 pairs of appendages Antennae – 1st two pairs, sensory functions Other 3 pairs are mouthparts, used for feeding 2 body regions: cephalothorax and abdomen

Crayfish Thorax has 5 pairs of walking legs Gills above walking legs 1st – pinching claw Gills above walking legs Cephalothorax covered by carapace Abdominal segments Swimmerets Final 2 segments – uropods and telson

Feeding and digestion Divided stomach – one end grinds, the other filters Green glands on head region excrete metabolic wastes Coelom reduced to space around reproductive system

Circulatory system Heart in pericardial cavity Blood carries respiratory pigment hemocyanin pumped to hemocoel (made of sinuses) Hemolymph flows into organs Open circulatory system

Nervous system Crayfish similar to earthworm Brain and ventral nerve cord Ganglia with paired lateral nerves

Reproduction Separate sexes Males Gonads ventral to pericardial cavity Coiled sperm duct at base of fifth walking leg Sperm transfer completed by first 2 pairs of swimmerets

Females Ovaries open at bases of 3rd walking legs Seminal receptacle between fourth and fifth walking legs Eggs attach to swimmerets of female

Insects

Body Structure Head, thorax, abdomen Head has pair of sensory antennae, pair of compound eyes, several simple eyes Mouthparts adapted to lifestyle

Abdomen holds most internal organs Thorax has 3 pairs of legs and wings (1 or 2 pairs, or none) Exoskeleton lighter and contains less chitin

Grasshopper 3rd pair of legs for jumping 2 pairs of wings Forewings tough/leathery Broad, thin hindwings (Lateral surface) 1st abdominal segment has tympanum for sound waves

Posterior region has 2 pairs of projections Female Posterior region has 2 pairs of projections Form ovipositor, which digs hole where eggs are laid

Feeding and Digestive System System suited for herbivorous diet Mouth chews food --> temporary storage in crop --> passed to gastric mill (finely ground) --> nutrients absorbed into hemocoel --> stomach --> intestine --> rectum --> anus

Excretory System Malpighian Tubules: extend into hemocoel and collect nitrogenous wastes Forms solid nitrogenous waste (Uric acid), conserving water

Respiratory System Spiracles: openings in exoskeleton Air enters trachae Branch until they end intracellularly Air pumped by alternating contraction/relaxation of body wall through bladder-like structures (attached to trachae near spiracles) Air enters anterior 4 spiracles and exits posterior 6 spiracles

Circulatory system Slender, tubular heart (lies against dorsal wall of abdominal exoskeleton) Pumps hemolymph into aorta, leading to hemocoel Circulates then returns to heart

Reproduction Male has penis Sperm passed to female and stored in seminal receptacle Internal fertilization prevents gametes/zygotes from drying out Fertilized eggs deposited in ground with ovipositor

Metamorphosis: change in form/physiology occurring as larvae (immature stage) becomes an adult Gradual Metamorphosis: gradual change in form as they mature Immature insect called a nymph

Complete Metamorphosis: drastic changes in form Begins a worm-like larva (caterpillar), then a case (cocoon), and finally becomes an adult Larvae and adults have different food sources

Comparison to crayfish

Crayfish Gills Oxygen carrying pigment in blood Excretes liquid nitrogenous waste (ammonia) Use uropods when swimming Grasshopper Trachae No pigment Excretes soild nitrogenous waste (Uric acid) Tympanum Penis that passes sperm Legs for hopping Wings for flying

Terrestrial spiders, scorpions, ticks, and mites Arachnids Terrestrial spiders, scorpions, ticks, and mites

Body structure Cephalothorax has 6 pairs of appendages Chelicerae Pedipalps 4 pairs of walking legs Thorax contains internal organs

Scorpions Oldest terrestrial Arthropods Live in tropics, subtropics, and temperate regions Nocturnal Pedipalps are long pincers, long abdomen ends with stinger

Ticks and Mites Parasites Suck blood of hosts Spread diseases like spotted fever or lyme disease

Spiders Narrow waist separates cephalothorax and abdomen Chelicerae have a fang that delivers venom Pedipalps assist in sensing or holding prey Digestive juices liquefy tissues, gets sucked into stomach Silk threads using for nesting and catching prey

Inner body wall form lamellae – known as book lungs Malpighian tubes work with rectal glands to reabsorb ions and water (prior to Uric acid excretion) Inner body wall form lamellae – known as book lungs Air flows into one side of lamellae and exchange gases with blood flowing in opposite direction