Bilaterians- Biodiversity
What are Bilaterians
These are all the animals that have biateral symmetry in their body rather than radial or no symmetry
How have Bilaterians developed
They only have 1 plane of symmetry in their body and the vast number of animals are bilaterians
They have a higher eumetazoa that have bilateral symmetry and also 3 tissue layers so are triploblasts
How do Bilaterians move
They locomote across an environement gradient in order to find food, mating partners and to avoid predators
This can be done due to the presence of head showing the cephalization hass taken place
The movement across gradienst causes the bilateral symmetry
Some Cnidariens evolve a degree of bilateral due to move across gradients
What is cephalization
Bilaterians can move across an environmental gradient due to polarity
There is a concentration of sensory organs at the front of the animal
Concentration of nervous system at the front of the animal to then form a head that allow directional movement
What is secondary radial symmetry
This happens when sessile bilaterains revert back to having radial symmetry
Such as in Echnoderms, Bryozoa and Annelids
How does bilaterain locomation take place
There are muscles that relax and contract
This means that a skeleton is needed in the form of an
endoskeleton in Vertbrates, Exoskeleton in arthropods or a hydrostatic skeleton
What is a hydrostatic skeleton
They are found in all Bilaterians where they allow crawling to peristaltic
This is an enclosed volume of fluid that is uses to support and counteract muscles
This is well adapted for aquatic or damp habitats
There is an antagonistic relaitionship between longitudinal and circular muscles
Where are the body cavities in bilaterians
In Annelids, molluscs, arthropods, echnioderms and chordates the cavity within the mesoderm
In roundworms and wheel animals the cavity between the mesoderm and endoderm
There is no body cavity in flat worms
What are Platyhelminthes
These are Flat worms
They are marine and freshwater as well as damp on land habitat
They have a dorsoventrally flattend body
Only 1 opening in the digestive system
They are parasites that suck onto vertabrates due to have 2 suckers
What are Tubellaria
Type of flat worm in the phylum
These are free living in mostly marine but some freshwater
They are carnivores
Best know is the Planarians
What are Planarien eye spots
They prefer and work better in the dark due
Contain photoreceptors that then fead to the brain via nerves
There is an ocellus round the eyes
How do Planarians reproduce
Can be asecually by fission and regeneration where they need 1/279 of the species to then form a fully new organsim via asexual reproduction
It can also happen via sexual rexual reproduction
Planarian Asexual reproduction
The more anterior the fragement then the faster it will regenerate a head
If a fragment is too small then it will lose polarity and form a janus head
What are Monogenea and Trematoda
They are both parasites that are adapted for parasitic life style
They have specialised suckers for attatchment
Their life cucle often involve multiple host species
What are Cestoda
These are highly adapted tapeworms
They have a Scolex head with hooks and suckers for attachment
Body made up of ribbon of proglottids each with multiple sex organs
They have multiple host in a life cycle
What is the Beef Tapeworm life cycle
Eggs or gravid proglottids in feces enter the environment and the cows become infested by eating contaminated vegatation
Oncospheres hatch and penetrate the intestine wall and enter the muscles
Humand are infected by eating raw infected meat, where then the scolex attach to the small intestine and they develop to adult tape worms there
What is the phylum Rotifa
These are triploblasts that are mostly freshwater and a few marine
They are an important part of plankton
Up to 2mm long and have a proper gut: mouth with cilia and an anus
Function as hydrostatic skeleton
How do Rotifer reproduce in favourable conditions
Only in females can reproduce through unfertilized eggs this is called parthenogenesis, these dont live very long
Embryos can also break dormancy to get female generation with smoe rotifa groups not forming a male in 35 million years
Rotifer reproduction in unfavourable conditons
Male and female eggs are produced so get a fertilized eg that then are cabaple to go dormant till get favourable conditions
What is the Lophotrocgozoa phylas
They have a crown of ciliated tentacles around the mouth
This is used for filter feeding due all species are aquatic
Due to this however they are sessile as they dont have a head due to the loss of cepha;isation and they have a U shaped gut
What are Ectoprocta
A Phyla of colonial animal that are lophotrochozoa
These are moss animals that are moslty marine but a few in freeshwater
They have a retractable lophophore
What are Brachiopoda
These are lamp shells that are all marine
They resemble clams but have 2 halves of shell that are dorsal ventral and not lateral, this is Convergent evolution
They have pediclde that anchor them to substrates
Have a lophomore so are filter feeders
What are Nemertea
These are Ribbon worms that sre 20-50cm long and mainly marine or moist soil
They are active swimmers or burrow in the sand
They havea proboscis for hunting along with contraction ciruclar muscles that push out the probosics when fluid pressure increases
What are Annelida
These are Segmented worms that live in the sea, fresh water or damp soil
There are 2 groups : Ploychaetes and Oligochaetes
Polychaetes have many hairs per segment and oligiochaetes have few hairs per segment
What is metameric segmentation
This is shown in annelida where there are 2 cavities per segment that are seperated by mesnetry
Segment are seperated by septae
Each cavity has its own excretory system
There is ladder like ventral nervous system with one ganglion per segment
How did segmentation evolve
It is unclear due to segmentation in many phyla
Once segmentation exist it can lead to specialisation between segments
In annelida sgemnetation goes back to common anscestor and in arthropods segmentation evolved seperatly
What are the annelida Polychaeta
These are mainly marine
Have a clear head region and each segment has parapodia and chaetae(Hair)
They can move by retrograde waves of parapodial power strokes alternatinjg between the left and the right
E.G Fan Worms, Christmas Tree worms,
What are Annelida Oligochaeta
These are earthworms spo freshwater,marine and land based
There is no clear head region and segments omly have chaetae but no legs
They move by peristalitc crawling
What are annelida- Hirudinea
These are leeches that are generally freshwater, and have reduced segmentation with no chaetae
They are blood suckers of intervtabrae and vertabrae hosts
This is due to have suckers with blad like jaw and are anaesthetic and anticoagulant
What are Tardigrada
These are waterbears and mossm piglets that are extremly small
Survive in extreme environments and have survived in space
An ancient groups due fossils from 530 mya
What are Nematoda
These are round worms and are unsegmented worms they are widespread in water, soil,plant and animal tissues
They have a fluid filled body cavity that is partially lined with mesoderm
Feed on decomposing material or bacteria
Can be parasites of plant and animals
How do nematoda move
BY longitudinal muscles that work against the fluid filled body cavity and cuticle
Cause a thrashing movement
Dont have circular muscles
What are C.elegans The Worm
The first amimal to have its genome cloned and they are transparent so can be observed easily
They have a fixed cell number of 959