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