Arthropods

Jointed-legged invertebrates

Arthropod Characteristics

Metamerism with tagmatization Chitinous exoskeleton Paired-jointed appendages Growth with ecdysis (molting) Ventral nervous system Open circulatory system Complete digestive tract Malpighian tubules for excretion

Evolutionary Significance

Protostomes Schizocoelous development Paired ventral nerve cord Loss of internal metamerism Increased tagmatization (specialization of

segments)

Terrestrial Dominance

Minimize water loss Exoskeleton Respiratory system development Advanced excretory system

Greater ability for movement Exoskeleton attaches strong muscles Support

Exoskeleton

Major reason for success of this group! Provides

Support Protection Prevention of dehydration Sites for muscle attachment

Exoskeleton Structure

Epicuticle (outer layer) Water tight Barrier

Procuticle (inner layer) Made of chitin

Allows for protection Forms joints

Ecdysis

Shedding or molting of exoskeleton New exoskeleton is soft Tanning (sclerotization) must take place to

make outer layer of procuticle hard

Metamorphosis

Change in body form from immature (larval) stages to adult forms

Reduces competition between stages for Food Living space

Larval forms often occupy different habitats than the adults do

Taxonomy of Arthropods

4 subphyla Trilobitomorpha (all extinct) Chelicerata Crustacea Uniramia

Trilobitomorpha

Trilobites All extinct All marine 3 sections

Chelicerata

Class Merostomata Horseshoe crabs Water scorpions (eurypterids)

Class Arachnida Spiders Mites Ticks Scorpions

Class Pycnogonida (sea spiders)

Chelicerate Characteristics

Two-part body Opisthosoma

Chelicerae (1st pair of appendages – forms feeding palps or fangs)

Pedipalps (2nd pair of appendages) Cephalothorax (prosoma)

Book lungs or book gills

Crustacea

Class Malacostraca Shrimp, lobsters, crayfish Isopods (wood lice – roly poly) Amphipods

Class Branchiopoda Fairy shrimp, brine shrimp Water fleas

Class Copepoda Cyclops (freshwater)

Class Cirripedia Barnacles Sacculina – parasite of crabs

Crustacean Characteristics

2 pairs of antennae Biramous appendages (Y-shaped) Segments are serially homologous

Uniramia

Class Diplopoda (millipedes) Class Chilopoda (centipedes) Class Pauropoda Class Symphyla Class Hexapoda (insects)

Insect Locomotion

Flight Walking (3+ legs on ground at all times) Running (Can run on 2 legs) Swimming (legs modified as paddles) Jumping (saltatory locomotion)

Insect Respiration & Circulation

Respiration Tracheae & spiracle system

Circulation Modified open circulatory system Some vessels Primitive Heart

Nervous System

Johnston’s organs (hearing - on antennae) Tympanic organs (hearing – on legs or body) Compound eyes (facets – ommatidia – fused) Simple eyes (ocelli)

Metamorphosis

Type Appearance Young called

Ametabolous larvae look like adults, just smaller

instars

Paurometabolous Specific number of molts

Nymphs (land)

Naiads (water)

Holometabolous Young very different from adults

Larvae

Economic Impact of Arthropods

1. Name one effect each major group has on mankind (good or bad).

2. For insects, list 4 good things that they do and 4 bad things that they are responsible for.