Arthropods

Question 1

What are the features of ecdysozoa?

Answer 1

> to grow they shed exoskeleton & expand
- moulting probably evolved only once
some have wormlike bodies covered by cuticle
(=thick, flexible exoskeleton)
thin cuticle allows exchange of gases but limits life to water

Question 2

What were Onychophora originally thought to be?

Answer 2

The missing link between annelids & arthropods

- now discredited

Question 3

What are the features of Onychophora?

Answer 3

Arthropod features:
Moulting & chitinous cuticle

Annelid features:
Soft, fleshy, non-jointed appendages & nephridia

Question 4

What are the features of ‘Water bears’ (the phylum Tardigrada)?

Answer 4

> anabiotic = greatly reduced metabolism 
> can dry or freeze
-273 to150 degrees
> survive x-ryas of 570,000
> survive vacuums or high pressure
> found everywhere

Question 5

What are the 5 common features of arthropods?

Answer 5

> exoskeleton
> moulting to grow 
> jointed limbs
> dorsal heart & ventral NS
> well-developed head (cephalisation)

Question 6

What do all arthropod limbs do?

What are the plates on their back called?

Answer 6

Chew

Tergites

Question 7

Describe an arthropod limb

Answer 7

Biramus = 2 branches
- inner & outer ramus

• many groups have lost exopod
• coxa has chewing surfaces

Question 8

What is tagmosis?

Answer 8

Specialising limbs in different segments

–> modified for different functions

Question 9

What are the palps of insects thought to be?

Answer 9

Remnants of limbs

Question 10

What are natural composites?

Answer 10

A mixture of biological materials

Either:
ceramic (e.g. calcium carbonate) & protein (teeth/bone/shell) phases
or
2 organic phases (protein + polysaccharide)

Question 11

Describe the composition of arthropod cuticle

Answer 11

Chitin in a protein matrix

Layers of chitin are arrange at small changes in angle
= strength in all directions

Covered in wax
= more resistant to water loss

Question 12

How do arthropods reduce the expensive cost of ecdysis?

Answer 12

Slough off cuticle
–> reabsorb as much cuticle as they can

Moulting gel liquifies internal layers of cuticle
–> only outer layers slough off

Question 13

Why are arthropods so successful?

Answer 13

> hard exoskeleton & ecdysis
> many limbs
> tagmosis
> many modifications of limbs
> complex sense organs
> most are small

Question 14

What are the 5 classes within Arthropoda?

Answer 14

Trilobita
Myriapoda
Chelicerata
Crustacea
Hexapoda

Question 15

What are the features of myriapods?

Give 2 examples

Answer 15

> many legs
> 2 tagmata - head & trunk 
> antennae, mandibles & 2 pairs of maxillipeds 
> all terrestrial 
> tracheal system 

e.g. centipedes (carnivores) & millipedes (herbivores)

Question 16

What are the features of chelicerates?

Give examples

Answer 16

> 2 tagmata - prosoma & opisthosoma
prosoma bears chelicerae, pedipalps & 4 pairs of walking legs

E.g. spiders, scorpions, mites & ticks

Question 17

What are chelicerae?

Answer 17

Pair of appendages in front of the mouth

Question 18

What are pedipalps?

Answer 18

2nd pair of appendages of chelicerates

- lateral to the chelicerae

Question 19

What are the features of crustacea?

Answer 19

> dominant marine arthropods
some partially/completely terrestrial
2 pairs of antennae, jaw-like mandibles, 2 pairs of maxillae & often extra feeding appendages (maxillipedes)

Question 20

What are mandibles?

Answer 20

Feeding mouthparts

Question 21

What are maxillae?

Answer 21

Paired structures on the head as mouthparts

- used for tasting and manipulating food

Question 22

What are the 3 major groups within crustacea?

Answer 22

Branchiopoda
Maxillopoda
Malacostraca

Question 23

What are the larvae of many large crustacea?

What are krill?

Answer 23

Planktonic

Shrimp-like marine planktonic arthropods
- major food source for many whales

Question 24

What are the features of hexapods?

Answer 24

> 1.5M described species
> primarily terrestrial
> head, throat & abdomen 
> antennae, mandibles & 2 pairs of maxillae
> 3 pairs of walking legs 
> tracheal system

Question 25

What are the subclasses within Hexapoda?

Answer 25

Apterygota
= wingless

Pterygota
= winged

Question 26

What are the 2 groups with Pterygota?

Answer 26

Hemimetabola
= incomplete metamorphosis

Holometabola
= complete metamorphosis

Question 27

What happens in hemimetabola?

Answer 27

Gradual changes occur between stages in metamorphosis

e.g. grasshopper

Question 28

What happens in holometabola?

Answer 28

Dramatic changes occur between stages in metamorphosis

e.g. moth

Question 29

Why arthropod species are most diverse?

Answer 29

Beetles

- approx 350,000 species

Question 30

Why are most insects small?

Answer 30

> helps parasitic insects avoid attentions of host
can use small living spaces
unavailable to larger insects

Question 31

Why aren’t there any huge insects?

Answer 31

> tracheal respiratory system 
> weight problems at ecdysis 
> vulnerability to predators
- heating up time
- increased time to maturity

Question 32

What are the 4 main features of a tracheal system?

Answer 32

Spiracles
Trachea
Tracheoles
Pulsating abdomen

Question 33

What does a study on 4 closely related beetle species reveal about the tracheal system?

Answer 33

Bigger beetles have greater fraction of body devoted to trachea than smaller ones

• opening into leg is a bottleneck
• space available for tracheae in leg limits size

Question 34

How has the pO2 in the atmosphere changed since the late Carboniferous?

Answer 34

High pO2 in late Carboniferous
- led to evolution of giant orgs in Permian

Now pO2 has decreased & is restrictive