Arthropods - Biodiversity
What are arthropods
They are the insects and crustecea animals
Highly diverse phylum of jointed limbed animals that first appeared in the cambrien era
Comprimise 2/3 of all animals species on earth
Have economic value to humans as disease vectors and Food security
Where are the arthropods on the animal tree
They are all triploblasts, Protostomia so the anus developed before the mouth that comes from the blastopore, They are ecdysozoa so have a 3 layered cuticle and they moult the exoskeleton as the animal grows
Why are arthropods the most succesful phyla
Due to Jointed appendages, Exoskeleton, Excretory system, Segmentation and Compound eyes are all present
What are Jointed appendages
They have jointed feet and jointed appendages so they can bend them for movement
There is usually 1 pair per somite but can be less
This allow the appendages to become specialsized for a a function
Why is the exoskeleton important for arthropods
The ecdysozoa act as the exoskeleton and is made up of 3 layers:
Epicuticle that is a water resistant protein, lipoprotein and wax
Exocutilce is scleritised where is needs to be hard and left flexible in other areas, made of protein and chitin
Endocuticle is mainly chitin and is mineralsied with calcium
What are pros and cons of an exoskeleton
The benefit is that prevent water loss and is strong but flexible due to made of protein and chitin
However a thincker exoskeleton needed for larger muscles so may limit the body size and have to moult to grow larger
What is Ecdysis
The shedding od anterior and posterior digestive tracts and compound eyes, as well the exoskeleton to alloow growth
The new exoskeleton will harden by scleritisation
Controlled by the hormone Ecdysome
Why is the excretory system important for arthropods
It is called Nephridia ans has the same function as Kindey so limit water loss
This is important for species living on land and marine environments
It will excrete nitrogenous waste that is not needed as Uric acid or Guanine
Why is Segmentation important
This is called Tagmosis where segments with a similar structure or function that may have appendages are organsied to tagmata
Get 3 tagmata in an insect = Abdomen , Thorax and Head that are made up in each tagamat of similar segmenst in the body
What are compound eyes and why are they important
These are formed eyes that have 100 of ommatidia that all contain corneal lens and a crystalline core
One ommatidia can lead to light passing to the Rhabdom that contain photoreceptors so many allow a large vision span and good image formation even at low light
Evolved in other phyla due to convergent evolution
What make up the arthropods
Hexapoda = Insect - 6 thoraic legs
Crustacea - Biramous limbs and mainly aquatic
Myriapoda - Many body segments with legs
Chilcerata - Chelicera for feeding and killing
Trilobites are 630 myo extant anscestor
What are Trilobites
First appeared in the cambrien era 530mta
Never left the sea so arent adapted to land
Classic invertabrae body plan
Have a calcium carbonate exoskeleton so have fossilized well
What are trilobites appendages
They have Biramous appendages, this means that exopod dorsal ones as well as endopod ventral ones
Present in Crustacea but others have lost thsese appandeages
Exopod much thicker and larger and endopod smaller thinner
What are the Chilicerata
70,000 species
Have anterior appendages that form chelicera that are fangs or pincers
These are sea spiders, horseshoe crabs, sea scorpions and arachnids
2ns most diverse group after insects
What are the Chelicerata eating habits
Sea Spiders = Feed on micro-organisms that grow on submerged surfaces using their cholicera
Horseshoe crabs= Live onn sea floor and feed on worms and molluscs
Arachnids = Most are predatory and they liquify there prey before they consume it and have large variety in capture method
What are the Chelicerata Tagmosis
They have a fused head and thorax to make a Cephaolothorax
They have 2 tagmata whihc are the anterior prosomo and the posterior opisthosoma
Have 8 legs
What are the pair of pedipalps on chelicerata
They have 1 fewer segment than legs and not used for locomotion
In male spiders they copulatory organs and have palpal bulb for sperm transfer
In scorpions they are used as pincers for capturing prey
In other chelicerata they act as antennae for taste and smell
What are book lungs in the Chelicerata
The air enter via a spiracle and go up and down between the muscle that go to and away from them
The blood enter and then leave in the intralameller blood space
They are found in Spider and Scorpions and Horseshoe crabs
Part of the exoskeleton
What are Mryiapods
These have a complex mouthpart and veyr modified legs
Such as centipedes and millipedes
What are millipedes
There are 1000 species and have 2 legs per segment
There are 36-750 legs
They are non-poisinous and moslty are detrivious eaters
They have ozopores that are stink glands
What are Symphyla and Pauropoda
Symphyla have 160 species and are less than 8mm long, they have 6 segment head then 14 segment body with legs on first 12 then silk spinning cerci on the 13th, they are blind
Pauropoda are less than 2mm long and also blind, they ahve 11-12 segments and 9-11 pair of legs, they do have forked antennae though
What are Crustacea
These are mainly marine and have biramous apendages
They have a 2nd antennae
Have mandible mouthparts
Lobsters, Crabs, Shrimp, isopods and Barnacles
What is Crustacea Tagmosis
3 Tagmata, a head, thorax and andomen
What is the Crustacea sub group- Xeonocarida
There are 36 species living in caves and aquifers
They have a well developed brain and olfactory senses
What is the crustacea sub group- Oligostraca
These are seed shrimp and there are 13,000 species of them
What are vericrustacea sub group of crustacea
These are true crustaceans and organsied in classes:
Branchiopoda= Fairy shrimp and water fleas
Maxillopoda = Barnacles
Malacostraca= Crabs, Lobsters and Woodlice
They have gills and have pincers