14. Arthropods

Question 0

Most diverse eukaryotic group?

Answer 0

Arthropods!

Question 1

Arthropods are in what group?

Answer 1

Ecdysozoans

Question 2

Name a few arhtropods to show how diverse they are.

Answer 2

• Sea spider
• Scorpion
• Crustaceans
• Centipede
• Insects: bees!

Question 3

Arthropods - segmentation?

Answer 3

Reduced

- Cephalothorax + abdomen

Question 4

Arthropods have jointed….

Answer 4

Appendages (each have specialized functions

Question 5

Body structure of arthropods?

Answer 5

Rigid exoskeleton

• non-living
• secreted by epidermis
• Covers all external surfaces, digestive tract, tracheae
• Composed of layers
• Composed of chitin, protein and CaCO3 (for crustaceans)

Question 6

Advantages of a rigid exoskeleton?

Answer 6

• Physical support
• Place for muscle attachment
• Physical protection (from abrasion, predation, parasite, desiccation)
• Pigments (camouflage, mating, etc.)
• Jointed appendages & exoskeleton allows faster locomotion
• Opportunity to change morphology between larval and adult stages

Question 7

Disadvantages of a rigid exoskeleton?

Answer 7

• Inflexible and heavy
• Impossible continuous growth in size - must be shed (moulted) periodically
• Requires energy (to form and shed)
• Prevents use of cilia as effectors
• Respiration through skin not possible - must have spiracles (pores) and tracheae

Question 8

In arthropods, mass grows …… and/but size changes ….

Answer 8

Mass: continuously
Size: stepwise fashion

Question 9

Musculo-Skeletal systems in arthropods

Answer 9

• Skeletal muscles: need a resistor to act against (a skeleton); are often found in antagonistic pairs

Question 10

4 major groups of arthropods? (under revision)

Answer 10

• Myriapods (millipedes, centipedes)
• Chelicerates (spiders, mites, scorpions)
• Crustaceans (marine)
• Hexapods (insects) (terrestrial)

Question 11

Body regions of myriapods?

Answer 11

2 - head + trunk

Question 12

Myriapods - feeding?

Answer 12

• Centipedes: carnivorous

- Millipedes: detritivores, herbivores

Question 13

Chelicerates - body regions

Answer 13

• Cephalothorax (has appendages)
• Abdomen (no appendages)
• –> no jaws, but mandibles

Question 14

Chelicerates - #1 appendages?

Answer 14

Chelicerae - fangs

Question 15

Chelicerates - #2 appendages

Answer 15

Pedipalps - copulatory organs, pincers

Question 16

Chelicerates - #3, 4, 5, 6 appendages?

Answer 16

Walking (4 pairs of walking legs)

Question 17

Daphnia are…

Answer 17

Crustaceans

Question 18

Where are crustaceans found?

Answer 18

Dominant in marine environment, but also in freshwater and terrestrial

Question 19

Crustaceans - body shape?

Answer 19

• Head + thorax (cephalothorax) + abdomen

- Appendages off each segments

Question 20

Crustaceans make up a large part of…

Answer 20

Zooplankton

Question 21

Hexapods = ….

Answer 21

Insects and other groups

Question 22

Hexapods - habitat?

Answer 22

Abundant in freshwater + land, very few marine

Question 23

Hexapods - body regions?

Answer 23

• Head (antennae, mouthparts)
• Thorax (3 pairs of walking liegs, may have wings)
• Abdomen (no appendages)

Question 24

Springtails are not …. but are considered to be ….

Answer 24

• Insects (internal mouthparts)

- A hexapod

Question 25

What is unique to insects?

Answer 25

External mouthparts

Question 26

Insect - feeding mode?

Answer 26

Herbivores, detrivitores, fluid-drinkers, predators, scavengers, parasites

Question 27

Wings have been …… by some insect species

Answer 27

Secondarily lost

Question 28

The wing of an insect and the gill of a crayfish are….

Answer 28

Homologous (common ancestral root)

Question 29

Insects (+most myriapods) respiratory systems?

Answer 29

Holes (spiracles) open into tubular tracheae which branch to finer tubes. Carry O2 to body cells

Question 30

Crustaceans - respiratory system?

Answer 30

Gills

Question 31

Chelicerates - respiratory system?

Answer 31

Some have spiracles & trachae, book gills (horseshoe crabs) or book lungs (spiders, scorpions)

Question 32

Arthropod circulatory system?

Answer 32

• Open
• Dorsal tubular heart (1 chamber) with pores (ostia); drives hemolymph into hemocoel spaces
• One-way valves

Question 33

Arthropods sexual reproduction

Answer 33

• Most species are dioecous and lay eggs

On land: internal fertilization (unless they use spermatophores - packets of sperm)
In water: internal (crabs) or external (barnacles)

Question 34

Metamorphosis of arthropods?

Answer 34

Moulting enables changes in morphology

Question 35

When do insects and crustaceans cease moulting?

Answer 35

Insects: as adults (metamorphosis to adult form may be complete or incomplete)

Crustaceans: continue moulting as adults

Question 36

Which one is not a disadvantage of having a cuticle to shed?

• Energy is required to shed exoskeleton
• Vulnerable to predation
• Body cannot continuously increase in mass
• Respiration through cuticle is not possible

Answer 36

3

for 4, see nematodes

Question 37

Complete metamorphosis =

Answer 37

Indirect or holometabolous development

Question 38

Complete metamorphosis characteristics?

Answer 38

• Abrupt changes in form (includes a “resting stage” - pupa)

- Often major habitat changes

Question 39

Incomplete metamorphosis = …

Answer 39

Gradual or hemimetabolous metamorphosis

Question 40

Incomplete metamorphosis characteristics?

Answer 40

• Gradual changes in form (no resting stage)

- Often no habitat change

Question 41

.

Answer 41

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