ARTHROPODA Flashcards
Lineage
Ecdysozoa
Key characteristics (7)
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
Subphyla, which are extant and which are extinct?
Hello Charlie, come meet Tilly!
1) Hexopoda (insects & relatives)
2) Chelliceriformes (chelicerates, class Eurypterida is EXTINCT)
3) Crustacea (crustaceans)
4) Myriapoda (centipedes and millipedes)
5) Trilobitomorphia (trilobites) EXTINCT
Describe the Chelicerate classes
MAPE
1) Arachnida (spiders)
2) Merostomata (horseshoe crabs)
3) Pycongonida (sea spiders
4) Eurypterida (sea scorpions) EXTINCT
Crustacean cuticles
Have a substantial mineral component.
Strong but heavy
OK in water
Insect cuticles
Waxy and waterproof, persistent moulting
eg. Silverfish
Diversity of sensory systems on insect cuticles
- ‘hairs’ for contact and vibration
- pores for taste and smell
- innervated for stress and strain
Distinguish between single lens and compound eyes
SINGLE LENS structure has cuticular lens, vitreous body, retina and tapetum
COMPOUND came in trilobite
Biramous vs uniramous limbs
Biramous have 2 branches, where one often modified to a gill
- most terrestrial arthropods have one branch
What are gnathobases?
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.
TAGMATISATION in Crustaceans
1) Middle of body
2) Posterior
1) movement and or gas exchange
2) gas exchange, very modified
Chelicerates have internalised their gills to form
book lungs
Insects, millipedes and some spiders have evolved novel gas exchange systems NOT derived from limbs
fine branching airways (tracheae), divided into tracheoles entering the body through spiracles
Is age useful for predicting arthropod success?
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
Can morphological potential (more segments) be used to show arthropod success?
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.
What drives species richness?
- Niche availability
- occupation of the same niche by different species in different places
Why have only terrestrial Arthropods developed plant detoxification metabolism?
Crustaceans feed on plant material with no chemical defence mechanism, describes radiation of Arthropods through Fahrenholz’s rule
Additional cause of insect species richness
1) FLIGHT allows adult insects to exploit small and patchily-distributed niches.
2) METAMORPHOSIS allows adults and larvae to occupy different niches
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?
1) no, can live in hypersaline
2) hard to prove
3) unlikely, works in fresh water
4) crustacea already there !!
1 branch in a biramous limb often develops into a (a). But most terrestrial Arthropods have (b) limbs
gill
Myriapods show very low ____ diversity
morphological
