Chordata Flashcards
What characterizes the phylum Chordata?
4 anatomic features
What does studying invertebrates in Chordata allow for?
Clues to the origins of vertebrates
What are the 3 subphyla of the phylum Chordata? Examples
1- Urochordata = tunicates
2- Cephalochordata = lancelets
3- Vertebrata = vertebrates
What are the 4 common features that all Chordatas have at some stage in their life?
1- Notochord
2- Dorsal hollow nerve cord
3- Pharyngeal slits
4- Post-anal tail
What is the notochord? When is it present? Where is it?
Present in all chordate embryos
Longitudinal, flexible rod
Between digestive tube and nerve cord
What is the notochord made from?
Large fluid-filled cells in stiff fibrous tissue
What does the notochord do?
Skeletal support
What does the notochord turn into in humans?
Gelatinous (Jelly) material of the disks between vertebrae
How does the dorsal hallow nerve cord develop?
In embryo - from plate of ectoderm that rolls into a tube
What does the dorsal hollow nerve cord develop into?
Central nervous system = brain and spinal cord
Where are the pharyngeal gill slits found? (3)
Connected to the pharynx, behind the mouth and to the outside of the animal
What does the pharyngeal gill slits do?
Allows water to enter mouth and exit without going through digestive tract
What does the pharyngeal slits function as in invertebrates of Chordata?
Suspension feeding devices
What does the pharyngeal gill slits turn into?
Slits and structures become - modified gas exchange (water vertebrates), jaw support, hearing and more
What is the post-anal tail?
Muscular tail that extends past the anus
What does the post-anal tail contain?
Skeletal elements and muscles
What does the post-anal tail do?
Pushing force for aquatic species
What is an example of the subphylum Urochordata?
Tunicates = sea squirt
Where are Urochordata found? How do they move?
Marine - sessile
How do Urochordata feed?
Suspension-feeders
Explain the process of suspension-feeding for Urochordatas
Water passes inside animal by
incurrent siphon -> gill slits -> ciliated chamber (atrium) -> food is trapped here -> water exits through excurrent siphon
What are Urochordata encased in?
In a tunic of cellulose-like carbohydrate
What of the 4 characteristics of Chordata are seen in young and adult Urochordata?
Young - all 4
Adult - only pharyngeal gill slits retained
What is an example of Cephalochordata?
Lancelets
What of the 4 characteristics of Chordata are seen in young and adult Cephalochordata?
Young = all 4 Adult = retain all 4
How do Cephalochordata feed? Explain
Suspension feeders - mucus nets across gills trap particles
How do Cephalochordata respire?
A little in part by pharynx and gill slits
Mainly across external body surface
Where are Cephalochordata found? Do they move?
Found tail end buried
Frequently move burrow sites by swimming
Explain how Cephalochordata swim
Contraction of chevron-shaped muscles flexes notochord and pushes body forwards
How are the chevron-shaped muscles used for swimming developed in Cephalochordata?
From blocks of mesoderm - called somites
Arranged along each side of notochord in embryos
What are the 2 stages of the evolution of vertebrates from invertebrates?
1- ancestral Cephalochordata evolved form oranges similar to larva form of Urochordata
2- vertebrates evolved from Cephalochordata
What is the hypothesis of Cephalochordata evolving from larva Urochordata?
Paedogenetic
Explain the hypothesis of Paedogenetic
Larva developed sexual maturity before metamorphism - if successful than natural selection would have reinforced this
Is there any evidence of the hypothesis Paedogenetic?
No evidence supporting or contradicting it
What are 3 distinct features of the subphylum Vertebrata?
1- head protected by cranium
2- backbone
3- bones
What else is unique to Vertebrata?
Neural crest cells
What are the 6 milestones of Vertebrata evolution?
1- cranium 2- backbone 3- jaws/lungs 4- 4 limbs = colonized land 5- amniotic eggs 6- mammary glands
What are Gnathostoma?
Jawed vertebrates
What does having a jaw mean for the Gnathostoma? (2)
1- wide range of feeding niches
2- evolved from gill arches in pharynx
How did vertebrates move onto land? Common ancestor?
Became tetrapods
Common ancestor shared with fleshy finned fish
What is the intermediate between an amphibian and a lobe-finned fish?
Tiktaalik
What happened to the amphibians after colonizing land?
Diversified out = age of amphibians
Though amphibians colonized land, they must spend most of life in water. Why?
They are dependent on water for reproduction
Would amphibians be able to survive and thrive in rainforests?
Yes = moist habitat for reproduction
How do amphibians respire?
Small lungs so have cutaneous gas exchange = gas exchange across moist skin
What developed next for amphibians to move away from water?
Amniotic eggs
What are amniotic eggs?
Drought-resistant = external water not necessary for production
What are the 4 extraembryonic membranes?
1- yolk sac
2- chorion
3- allantois
4- amnion
What is inside the amnion of an egg?
Amnion is the member with Amniotic cavity filled with amniotic fluid which protects the developing embryo
Explain the allantois of the egg
Stores excreted waste of the developing embryo
What is the yolk of the egg for? Where is it?
Nutrients and energy for the embryo
Contains within yolk sac
What is the chorion of an egg?
Outside membrane before shell
How are amniotes (eggs) classified?
How many temporal arches and opening on their skull
What are the 5 groups of diapsids (reptiles)?
1- tuataras 2- lizards 3- snakes 4- crocodiles 5- birds
What are synapsids?
Mammals
How do we distinguish diapsids (reptiles) for synapsids (mammals)?
All synapsids have mammary glands
What are 2 other features to distinguish a mammal?
1- fur or hair
2- endothermy
What is fur and endothermy? How is it used?
Endothermy - maintain body temp with metabolism
Homeothermy - maintain body temp requires fur
What is the hypothesized reason as to why humans don’t have fur?
Reduce number of external parasites
Mammals are divided into 3 groups, what are they?
Monotremes
Marsupials
Eutherials
What are monotremes? Milk?
Egg-laying mammals
Milk secreted by mammary glands into milk patched
What are marsupials?
Short gestation = young born underdeveloped and at birth crawl to mammary the gland to suckle milk
What are Eutherials?
Longer gestation = developed at birth and weaned at early aged
Explain the yolk of Eutherials
Reduced as embryo is nourished by mother’s blood = had placenta
How are marsupials embryo nourishment different than Eutherials?
By yolk sac placenta = limited resources
