Ch. 15 Notes

The Arthropods: Part 2

Phylum Arthropoda Review

5 Subphyla:1. Trilobitomorpha – extinct – trilobites– Marine– Cambrian-Carboniferous time period

2. Chelicerata – spiders, mites, ticks, horseshoe crabs, sea spiders, scorpions

3. Crustacea – ‘hard shelled’ – crayfish, shrimp, lobster, crabs, water fleas, barnacles

4. Myriapoda – millipedes & centipedes5. Hexapoda – ‘six legs’ – insects & their relatives

Subphylum Myriapoda

• Class Diplopoda – two-fold foot– Millipedes – 11-100 trunk segments– Two pairs of appendages on each trunk segment– Actually the fusion of two segments

• 2 ostia – opening @ end of oviduct• 2 ganglia• 2 tracheal trunks – part of circulatory system –

transports O2

– Glands produce Hydrogen Cyanide to repel other animals

– Round bodies in cross section

Subphylum Myriapoda

• Class Chilopoda – lip foot– Centipedes– Nocturnal– Flattened bodies in cross section– Poison claws– Only 1 pair of appendages per segment– Add legs and segments with each molt

Subphylum: Hexopoda

• Includes Insects & their relatives• Body divided into 3 Tagmata: – Head, thorax, abdomen

• 5 pairs of head appendages• 3 pairs of legs on the thorax (6 legs)

Class Insecta

Habitat:• terrestrial, aquatic, & aerial– Insects are the most successful land animals

Class Insecta

Locomotion• Flight is the most important form of locomotion– Insects were 1st animals to fly– Must be able to thermoregulate

• Maintain body temperatures different from environment

• Walk/Run• Jump• Swim

Class Insecta

Thermoregulation• Ectotherms– Most insects– Rely on sun or warm surface

• Heterotherms– Rely on metabolic heat– Shivering Thermogenesis• Generate heat by rapid contraction of flight muscles

Class Insecta

Digestive Tract• Long & Straight• 3 Regions

– Foregut• Musculary pharynx/oral cavity• Used for sucking fluids• Crop (storage)• Gizzard (regulates movement to midgut; grinds food)

– Midgut• Surface for digestion & absorption

– Hindgut• The Intestine• Reabsorption of Water

Class Insecta

Excretory System• Nitrogenous wastes

converted to uric acid– conserves water– energetically expensive

• Malpighian tubules transport uric acid to the digestive tract

Class Insecta

Respiration – a Simple System• Have trachea- chitin lined tubes– Open to outside through spiracles – Oxygen diffuses from trachea to body tissues

• Aquatic insects– Spiracles are nonfunctional – Gasses diffuse across body wall

• Blood is not important for gas exchange in insects

Class Insecta

Do insects have blood?

Circulatory System• Open Circulatory System• Less developed blood vessels• Blood distributes nutrients, hormones, &

wastes

Class InsectaNervous Communication• Pheromones – Chemicals

released by one individual that affects the behavior of another– Chemoreceptors – pores

through which chemicals diffuse • Feeding• Selection of egg laying sites• Mate location• Social organization

Class Insecta

Nervous Communication Continued…• Hormones regulate

– Ecdysis– Metamorphosis

• Eclosion – the emergence of an insect from a cocoon, chrysalis, or puparium– Cocoon- Protective case enclosing the

pupal stage, made of silk– Chrysalis- Last larval exoskeleton

maintained during the pupal stage– Puparium- an outer covering that

protects the pupae of some flies

Class Insecta

Nervous Communication Continued…

• Insects are capable of memory• Johnston’s organs – the base of

the antennae of most insects– Long setae that vibrate when certain

frequencies of sound strike them – Mosquitoes and fruit flies hear using

the Johnston's organ

Class Insecta

Nervous Communication Continued…• Sense organs– Mechanoreceptors – perceive physical

displacement of the body or body parts– Setae – distributed over mouthparts, antennae,

legs• Touch, air movements, and vibrations move setae

– Stretch Receptors – located @ joints & muscles• Monitor position and posture

Class Insecta

Nervous Communication Continued…

Sound• Tympanic organs– Consist of a thin, membrane

covering a large air sac– Air sac acts as a resonating

chamber– Sensory cells under membrane

to detect pressure waves

Class Insecta

Nervous Communication Continued…Sight• All insects are capable of detecting light• Compound Eyes

– Well developed eyes– Not a very good image– Good at detecting movement– Sometimes can detect polarized light– Made up of 1000’s of Ommatidia

• Each is a lens w/ a crystaline cone• Cells have a rhabdom light collecting area

– Converts light energy into nerve impulses

• Ocelli – simple eyes– Hundreds of photo receptors

Class Insecta

Reproduction• Adaptations for land– Resistant eggs– External genitalia– Behavioral mechanisms

that bring males and females together at appropriate times• Pheromones• Visual signals• Auditory signals

Class Insecta

Relationships• Many insects are social– They live in colonies– Each kind of individual in an insect colony is called

a caste• Many are beneficial to humans• Few are parasites or transmit diseases to

humans or plants