Biodiversity 4: Transition to the Chordates Flashcards
Describe the phylum echinodermata
Starfish, sea cucumbers, sea urchins etc.
Adults (almost) radially symmetrical but larvae bilateral
Often radiate from a central disc with 5 arms (pentamerous symmetrical)
Endoskeleton made of calcareous plates
Water vascular system comprises canals and tube feet that function in locomotion, feeding & gas exchange
No brain, sessile or slow moving
Describe the digestive system of the Echinodermata
Mouth on bottom, anus on top
Starfish have 2 stomachs:
Lower is everted out of the mouth and starts to digest food outside the body
Then passed into 2nd upper stomach where its broken down by enzymes
Passes along arms to digestion glands
Waste ejected through anus
Describe the reproductive system of the Echinodermata
Sexes are separate
External gamete release
Describe the tube feet of an Echinoderm
Ring canal runs around body centre
Connected to radial canals in arms
Off the radial canal are tube feet
Each foot has an amupula at the top, when squeezed the feet extend through the bottom of the arm
Tube feet collect food and allow movement
Coordination of feet occurs through a nerve net
What do starfish generally prey on?
molluscs, particularly bivalves
How do starfish feed?
Use arms and tube feet to pry open shells
Describe brittle stars
Distinct central disc
Longer arms than a starfish
Highly mobile by thrashing arms
Some are suspension feeders, others are predators, others are scavengers
Describe feather stars
Sedentary, attached to substrate
Use arms for suspension feeding
Very old
Describe sea urchins
Have no arms
Have 5 spoke-like rows of tube feet radiating from centre
Move slowly
Describe sea cucumbers
Soft bodied, elongated
Reduced endoskeleton
Tube feet around mouth → adapted for feeding
Describe a sea daisy
Living on waterlogged wood in deep seas
Recent discovery
Tube feet
Give some examples of echinoderms
starfish
brittle stars
feather stars
sea urchins and sand dollars
sea cucumbers
sea daisys
Define notochord
Notochord → long flexible rod lies between digestive tract and nerve chord in embryo, skeletal support
Define dorsal hollow nerve chord?
Dorsal hollow nerve chord → a rolled up plate of dorsal ectoderm
What are Pharyngeal slits?
Pharyngeal slits → slits in the ‘throat’ region of the digestive tract that allow water to pass through without going to the stomach
What is the muscular post-anal tail?
Muscular post-anal tail → tail extends beyond anus
Describe the Urochordates
tunicates or ‘sea squirts’
Adult form in sessile
U-shaped filter feeder
Pharynx with numerous slits (has only 1 of the chordate features)
But, free-living larva has all of the chordate features
Describe the Cephalochordates
lacelets, Branchiostoma
All 4 chordate features in adult stage
Swim with side-side undulations similar to fish
No real head, brain, sensory organ, heart jaws or fins
Mouth surrounded by cirri that strain and direct food to mouth, food is then collected in the pharyngeal slits
Molecular evidence suggests which subphylum is our closest invertebrate relative?
Cephalochordata
Both cephalochordates and vertebrates may have evolved from the larval form of ____________ by paedogenesis
urochordate
What is paedogenesis?
Sexual maturity in larva
Describe the characteristics of vertebrates
Vertebral column forms main axis of the body
Well developed brain and sensory organs in the head
Closed circulatory system with ventral chambered heart
