Untitled Quiz

Arthropods

• 75% of animals are arthropods
• 1.2 million described species
• Subphylum Hexapoda includes insects
• Subphylum Chelicerata includes spiders, scorpions, mites, horseshoe crabs, and sea spiders
• Subphylum Crustacea includes shrimps, crabs, copepods, and barnacles
• Subphylum Myriapoda includes centipedes and millipedes
• Subphylum Trilobita includes trilobites (extinct)
• Arthropods evolved from Panarthropods (Onychophorans and Tardigrades)
• Crustaceans are the most ancient group of arthropods
• The first arthropods to move onto land were Chelicerates in the Ordovician Era
• Myriapods moved onto land in the Silurian Era
• Hexapods moved onto land in the Devonian Era
• Hexapods were the most successful at colonizing land

Arthropod Characteristics

• Bilaterally symmetrical and triploblastic
• Segmented bodies with jointed appendages
• Chitinous exoskeleton that is molted
• Dorsal anterior brain and ventral nerve cord
• Well-developed sensory organs
• Coelom reduced
• Complex gut with specialized regions
• Movement by skeletal muscles attached to exoskeleton
• Open circulatory system (except for some details)
• Various excretory organs
• Primarily dioecious, with mixed and direct development
• Range in size from microscopic to 4 meters
• Homologous structures (e.g., crab antennae, scorpion chelipeds)

Exoskeleton

• Jointed legs evolved for movement because exoskeleton restricted movement
• Provides protection from predators and allows it to be a predator
• Layers of cuticle: Epicuticle (thin outer layer), Procuticle (thick inner layer made of chitin-protein), Exocuticle (thicker chitin layer), Endocuticle (inner layer).
• Epicuticle aids in water loss prevention in terrestrial arthropods (e.g., contains waxes)
• Hypodermis secretes the new cuticle

Molting

• Molting is the process of shedding the old exoskeleton and growing a new one
• Stages include pre-molt (hormone secretion, breakdown of old cuticle), active secretion phase, de-calcification (in crustaceans), and post-molt (cuticle hardening)

Digestive System

• Complete digestive tract (foregut, midgut, hindgut)
• Foregut: mechanical and chemical breakdown
• Midgut: chemical breakdown and absorption
• Hindgut: water absorption and feces preparation

Circulatory System

• Open circulatory system
• Hemolymph (arthropod blood) transports nutrients, wastes, and hormones. Gases are not transported in insects.
• Hemocyanin and hemoglobin are blood pigments

Respiration

• Book lungs and trachea in terrestrial arthropods
• Book lungs: stacked plates with air pockets to aid in gas exchange
• Trachea: branching tubes for air delivery
• Lamellae in book lungs, thin membranes aiding in gas exchange

Excretion

• Variety of excretory organs based on the habitat. Not detailed (pseudotrachea described)

Nervous System

• Mechanoreceptors detect stimuli (e.g., touch, pressure, sound)
• Often have simple eyes (eyespots to compound eyes)
• Sensory hairs, bristles, and sensilla are important structures

Reproduction

• Dioecious (separate sexes)
• Mostly internal fertilization

Development

• Types: indirect, mixed, direct
• Dependent on the environment