Lecture 10 - Arthropods - 1 Flashcards
how big is the group?
largest group of animals
what is a big feature of the group?
they are metamerically segmented with appendages on segments
what is tagmatisation?
groups of segments e.g. head, thorax, abdomen - each section is tagmata
what are hox genes and when were they first discovered
first discovered in an arthropod - drosophila
- control anterior-posterior axis
- tell cells in body which segment they are in and what they are going to be by coding for regulatory proteins
how have arthropods adapted to be resilient to desiccation and move onto land?
they have a cuticle secreted by the epidermis
describe the 2 parts of the cuticle
epicuticle - at the top made up of proteins and wax - waterproofing layer
procuticle - made up of exo,endo and mesocuticle - the exocuticle is a tanned glycoprotein making it very strong
describe arthropod locomotion
- not peristalsis due to hard covering
- muscles attached directly to cuticle
- appendages have a thinner cuticle
arthropod circulation
haemocoel - have a heart but is open circulatory
arthropod gas exchange
special structures because cuticle is impermeable allowing no diffusion
how do arthropods grow?
process called ecdysis - shed old cuticle and grow a new one - molting is when new features will form in development from young - epicuticle is shed because tanning makes it too tough to be broken down - endocuticle is digested by enzymes secreted by epidermis
what limits the size of arthropods
the cuticle - because if they grew large they would need a thick cuticle which would be too heavy
why is the new cuticle very soft?
allows the animals to grow - they make the cuticle bigger than themselves by absorbing water or puffing themselves up with air which they get rid of when the cuticle hardens
describe the oldest group of arthropods
trilobites
- 3 body regions (head thorax tail)
- compound eye
- binamous limbs
describe the chelicerates
- 2 body regions (prosoma, opithosoma)
- 6 pairs of appendages
- chelicera = pincers and pedipalp = first walking leg
marine chelicerates
horseshoe crab - only survivors out of sea scorpion group - very unusual
- blue blood with lots of amoeebocytes acting like RBCs
terrestrial chelicerates
arachnids - scorpions, mites, ticks and spiders
how do most arachnids feed
mostly carnivorous and use some kind of toxin to kill prey
4 facts about scorpions
- earliest group of arachnids
- chelicera v reduced and pedipalps are massive
- reproduction - internal fertilisation - male drops a spermatophore
- stinging tail which injects neurotoxin
6 facts about spiders
- chelicera are modified into fangs which deliver toxins
- pedipalps are important in mating
- spin silk produced by silk glands - made of protein fibroin
- usually have 8 eyes
- book lung for gaseous exchange - some also have tracheae system
- malphigian tubules as excretory device
use of silk by spiders
- ballooning for travel
- gifts for females
- wrapping offspring
can make the silk a different consistency depending on what they need it for
describe mites
free living and parasitic forms
- dust mites eat dead human skin - live in mattresses- faeces contain allergens
- varroa - feed on haemolymph of honey bees - can cause collapse of a colony
describe ticks
ectoparasites - fill up their abdomen with blood of vertebrates
- can transmit lyme disease - effects nervous system
what are sea spiders called and whats different about them?
pycnogonids - most of body is prosoma - opisthosoma is tiny
