Arthropods Flashcards
What are the features of ecdysozoa?
> 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
What were Onychophora originally thought to be?
The missing link between annelids & arthropods
- now discredited
What are the features of Onychophora?
Arthropod features:
Moulting & chitinous cuticle
Annelid features:
Soft, fleshy, non-jointed appendages & nephridia
What are the features of ‘Water bears’ (the phylum Tardigrada)?
> anabiotic = greatly reduced metabolism > can dry or freeze -273 to150 degrees > survive x-ryas of 570,000 > survive vacuums or high pressure > found everywhere
What are the 5 common features of arthropods?
> exoskeleton > moulting to grow > jointed limbs > dorsal heart & ventral NS > well-developed head (cephalisation)
What do all arthropod limbs do?
What are the plates on their back called?
Chew
Tergites
Describe an arthropod limb
Biramus = 2 branches
- inner & outer ramus
- many groups have lost exopod
- coxa has chewing surfaces
What is tagmosis?
Specialising limbs in different segments
–> modified for different functions
What are the palps of insects thought to be?
Remnants of limbs
What are natural composites?
A mixture of biological materials
Either:
ceramic (e.g. calcium carbonate) & protein (teeth/bone/shell) phases
or
2 organic phases (protein + polysaccharide)
Describe the composition of arthropod cuticle
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
How do arthropods reduce the expensive cost of ecdysis?
Slough off cuticle
–> reabsorb as much cuticle as they can
Moulting gel liquifies internal layers of cuticle
–> only outer layers slough off
Why are arthropods so successful?
> hard exoskeleton & ecdysis > many limbs > tagmosis > many modifications of limbs > complex sense organs > most are small
What are the 5 classes within Arthropoda?
Trilobita Myriapoda Chelicerata Crustacea Hexapoda
What are the features of myriapods?
Give 2 examples
> many legs > 2 tagmata - head & trunk > antennae, mandibles & 2 pairs of maxillipeds > all terrestrial > tracheal system
e.g. centipedes (carnivores) & millipedes (herbivores)
What are the features of chelicerates?
Give examples
> 2 tagmata - prosoma & opisthosoma
prosoma bears chelicerae, pedipalps & 4 pairs of walking legs
E.g. spiders, scorpions, mites & ticks
What are chelicerae?
Pair of appendages in front of the mouth
What are pedipalps?
2nd pair of appendages of chelicerates
- lateral to the chelicerae
What are the features of crustacea?
> dominant marine arthropods
some partially/completely terrestrial
2 pairs of antennae, jaw-like mandibles, 2 pairs of maxillae & often extra feeding appendages (maxillipedes)
What are mandibles?
Feeding mouthparts
What are maxillae?
Paired structures on the head as mouthparts
- used for tasting and manipulating food
What are the 3 major groups within crustacea?
Branchiopoda
Maxillopoda
Malacostraca
What are the larvae of many large crustacea?
What are krill?
Planktonic
Shrimp-like marine planktonic arthropods
- major food source for many whales
What are the features of hexapods?
> 1.5M described species > primarily terrestrial > head, throat & abdomen > antennae, mandibles & 2 pairs of maxillae > 3 pairs of walking legs > tracheal system
What are the subclasses within Hexapoda?
Apterygota
= wingless
Pterygota
= winged
What are the 2 groups with Pterygota?
Hemimetabola
= incomplete metamorphosis
Holometabola
= complete metamorphosis
What happens in hemimetabola?
Gradual changes occur between stages in metamorphosis
e.g. grasshopper
What happens in holometabola?
Dramatic changes occur between stages in metamorphosis
e.g. moth
Why arthropod species are most diverse?
Beetles
- approx 350,000 species
Why are most insects small?
> helps parasitic insects avoid attentions of host
can use small living spaces
unavailable to larger insects
Why aren’t there any huge insects?
> tracheal respiratory system > weight problems at ecdysis > vulnerability to predators - heating up time - increased time to maturity
What are the 4 main features of a tracheal system?
Spiracles
Trachea
Tracheoles
Pulsating abdomen
What does a study on 4 closely related beetle species reveal about the tracheal system?
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
How has the pO2 in the atmosphere changed since the late Carboniferous?
High pO2 in late Carboniferous
- led to evolution of giant orgs in Permian
Now pO2 has decreased & is restrictive
