Biodiversity 4: Transition to the Chordates

Question 1

Describe the phylum echinodermata

Answer 1

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

Question 2

Describe the digestive system of the Echinodermata

Answer 2

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

Question 3

Describe the reproductive system of the Echinodermata

Answer 3

Sexes are separate
External gamete release

Question 4

Describe the tube feet of an Echinoderm

Answer 4

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

Question 5

What do starfish generally prey on?

Answer 5

molluscs, particularly bivalves

Question 6

How do starfish feed?

Answer 6

Use arms and tube feet to pry open shells

Question 7

Describe brittle stars

Answer 7

Distinct central disc
Longer arms than a starfish
Highly mobile by thrashing arms
Some are suspension feeders, others are predators, others are scavengers

Question 8

Describe feather stars

Answer 8

Sedentary, attached to substrate
Use arms for suspension feeding
Very old

Question 9

Describe sea urchins

Answer 9

Have no arms
Have 5 spoke-like rows of tube feet radiating from centre
Move slowly

Question 10

Describe sea cucumbers

Answer 10

Soft bodied, elongated
Reduced endoskeleton
Tube feet around mouth → adapted for feeding

Question 11

Describe a sea daisy

Answer 11

Living on waterlogged wood in deep seas
Recent discovery
Tube feet

Question 12

Give some examples of echinoderms

Answer 12

starfish
brittle stars
feather stars
sea urchins and sand dollars
sea cucumbers
sea daisys

Question 13

Define notochord

Answer 13

Notochord → long flexible rod lies between digestive tract and nerve chord in embryo, skeletal support

Question 14

Define dorsal hollow nerve chord?

Answer 14

Dorsal hollow nerve chord → a rolled up plate of dorsal ectoderm

Question 15

What are Pharyngeal slits?

Answer 15

Pharyngeal slits → slits in the ‘throat’ region of the digestive tract that allow water to pass through without going to the stomach

Question 16

What is the muscular post-anal tail?

Answer 16

Muscular post-anal tail → tail extends beyond anus

Question 17

Describe the Urochordates

Answer 17

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

Question 18

Describe the Cephalochordates

Answer 18

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

Question 19

Molecular evidence suggests which subphylum is our closest invertebrate relative?

Answer 19

Cephalochordata

Question 20

Both cephalochordates and vertebrates may have evolved from the larval form of ____________ by paedogenesis

Answer 20

urochordate

Question 21

What is paedogenesis?

Answer 21

Sexual maturity in larva

Question 22

Describe the characteristics of vertebrates

Answer 22

Vertebral column forms main axis of the body
Well developed brain and sensory organs in the head
Closed circulatory system with ventral chambered heart