ARTHROPODA

Question 1

Lineage

Answer 1

Ecdysozoa

Question 2

Key characteristics (7)

Answer 2

1) chitinous skeleton
2) show tagmatisation
3) show segmentation with paired appendages
4) body circulation is open (haemocoel)
5) head has pair of compound eyes
6) paired ventral nerve cords, ganglion in each segment
7) growth by moulting

Question 3

Subphyla, which are extant and which are extinct?

Hello Charlie, come meet Tilly!

Answer 3

1) Hexopoda (insects & relatives)
2) Chelliceriformes (chelicerates, class Eurypterida is EXTINCT)
3) Crustacea (crustaceans)
4) Myriapoda (centipedes and millipedes)
5) Trilobitomorphia (trilobites) EXTINCT

Question 4

Describe the Chelicerate classes

MAPE

Answer 4

1) Arachnida (spiders)
2) Merostomata (horseshoe crabs)
3) Pycongonida (sea spiders
4) Eurypterida (sea scorpions) EXTINCT

Question 5

Crustacean cuticles

Answer 5

Have a substantial mineral component.

Strong but heavy
OK in water

Question 6

Insect cuticles

Answer 6

Waxy and waterproof, persistent moulting

eg. Silverfish

Question 7

Diversity of sensory systems on insect cuticles

Answer 7

• ‘hairs’ for contact and vibration
• pores for taste and smell
• innervated for stress and strain

Question 8

Distinguish between single lens and compound eyes

Answer 8

SINGLE LENS structure has cuticular lens, vitreous body, retina and tapetum
COMPOUND came in trilobite

Question 9

Biramous vs uniramous limbs

Answer 9

Biramous have 2 branches, where one often modified to a gill

- most terrestrial arthropods have one branch

Question 10

What are gnathobases?

Answer 10

Seen in horseshoe crabs, a joint or process of the proximal part of the appendage of an arthropod modified to aid in carrying or masticating food.

Question 11

TAGMATISATION in Crustaceans

1) Middle of body
2) Posterior

Answer 11

1) movement and or gas exchange

2) gas exchange, very modified

Question 12

Chelicerates have internalised their gills to form

Answer 12

book lungs

Question 13

Insects, millipedes and some spiders have evolved novel gas exchange systems NOT derived from limbs

Answer 13

fine branching airways (tracheae), divided into tracheoles entering the body through spiracles

Question 14

Is age useful for predicting arthropod success?

Answer 14

NO (not for richness)
- Crustaceans and Chelicerates are both much more diverse than insects AND OLDER

BUT… myriapods are also ancient but have low morphological diversity

Question 15

Can morphological potential (more segments) be used to show arthropod success?

Answer 15

Crustaceans and chelicerates have lots of segments and are morphologically diverse.

BUT Myriapods have lots of segments but have remained
morphologically the same throughout their long history.

Question 16

What drives species richness?

Answer 16

• Niche availability

- occupation of the same niche by different species in different places

Question 17

Why have only terrestrial Arthropods developed plant detoxification metabolism?

Answer 17

Crustaceans feed on plant material with no chemical defence mechanism, describes radiation of Arthropods through Fahrenholz’s rule

Question 18

Additional cause of insect species richness

Answer 18

1) FLIGHT allows adult insects to exploit small and patchily-distributed niches.
2) METAMORPHOSIS allows adults and larvae to occupy different niches

Question 19

Why aren’t there more marine insects?

1) Is it due to salt?
2) insect breakthroughs inappropriate? eg. no use for wings
3) Canʼt cope with permanent aquatic-ness? Tracheal system, once evolved, not good in the sea?
4) Why then?

Answer 19

1) no, can live in hypersaline
2) hard to prove
3) unlikely, works in fresh water
4) crustacea already there !!

Question 20

1 branch in a biramous limb often develops into a (a). But most terrestrial Arthropods have (b) limbs

Answer 20

gill

Question 21

Myriapods show very low ____ diversity

Answer 21

morphological