Arthropods (Phylum Arthropoda)

Question 1

What are the defining features of arthropods that have made them so successful?

Answer 1

1. Jointed appendages allowing range of movements.
2. Cuticular exoskeleton
3. Segmented body, with functionally specialized segments
4. Open circulatory system
5. Respiration via body surface, gills, trachae, or book-lungs
6. Paired excretory glands called malpighian tubules (excrete Uric acid as opposed to ammonia and urea, which are more toxic)
7. Advanced endocrine system
8. Show metamorphosis
9. Most species-diverse and habitat-diverse phylum. FIRST TERRESTRIAL ANIMALS

Question 2

What are the characteristic organs for respiration and excretion in arthropods? What kind of circulation do they have?

Answer 2

Circulation and respiration- open circulation. Blood with respiratory pigments or hemoglyph consisting of mostly plasma
Gas exchange- Book gills or book lungs. Tracheal system in some consisting of thin-walled tubes opening to outside via spiracles and ending directly on cells
Excretion- Prodominant waste product is uric acid-less toxic than ammonia and urea- can be temporarily stored and does not need water for dilution. Malpighian tubules absorb waste materials from hemoglyph and empty into hindgut

Question 3

How do insects thermoregulate?

Answer 3

Generally ectotherms (use external heat source for temperature regulation) but some can generate heat by muscular contraction
Social insects such as honeybees can increase hive temperature by tight clustering and decrease it by fanning their wings

Question 4

What kind of sense organs are seen in arthropods?

Answer 4

Mechanoreceptors called sensilla on antennae, legs. Auditory reception via sensilla or tympanal organ which detects vibrations
Chemoreception (taste, smell) via sensory cells on mouthparts, antennae, legs
Visual reception via compound eyes which have many ommatidia (photoreceptor unit)

Question 5

What are the three kinds of metamorphosis that you see in insects? Which hormones are involved in controlling metamorphosis?

Answer 5

Ametabolous (direct) development with young (juveniles)- similar to adults except in size and sexual maturation
Hemimetabolous (incomplete)- metamorphosis with young called nymphs which are wingless (grasshoppers, mayflies)
Homometabolous (complete)- has 3 distinct stages: larva (growth), pupa (differentiation), and adult (reproduction)- No further molting in adults. Butterflies, beetles

Controlled by 2 hormones: ecdysone and juvenile hormone

Question 6

What are the characteristic features of social insects? Which insects show social behavior?

Answer 6

Consist mostly of females, only one of which is sexually mature- the queen- and the rest are sexually inactive or sterile workers
Ants, bees, wasps, termites

Question 7

How are arthropods important?

Answer 7

Copepods, crustaceans, and insects all important components of food webs
Adversely affect human health as well as valuable products such as wax, honey, silk, and services such as pollination, biological control, soil turnover, decay, etc.