Echinodermata 2

Question 1

Summary

5 Classes

Answer 1

Crinoidea
Asteroidea
Ophiuroidea
Echinoidea
Holothuroidea

Question 2

Class Crinoidea

10 points

Answer 2

1. Retained ancestral body posture - oral surface directed upwards
2. 625 described species in 5 orders
3. Five basic arms - may be up to 200
4. Simple water vascular system
   No ampullae to operate podia
   No madreporite
5. Globose body attached by aboral stalk
6. Mouth and anus on oral surface
   creates U-shaped gut.
7. Anal cone stops faeces from entering the mouth.
8. Limited ring and radial canals.
9. Ossicles reduced
10. Food grooves present [help direct food to mouth]

Tube feet capture food

Moved to ambulacral groove

Carried to mouth in mucus

Question 3

Class Asteroidea

7 points

Answer 3

1. Stellate, flattened body
2. 1,500 described species in 7 orders
3. Five basic arms - may be up to 40
4. Developed water vascular system[important for movment]
5. Unattached and freely mobile
6. Mouth on downwards oral surface; madreporite and anus (when present) on aboral surface

7. Reproduction
Typically dioecious 
Some of hermaphroditic 
Fertilisation external
Massively fecund {fertile} up to 2.5 million eggs released

Question 4

Class Ophiuroidea

9 points

Answer 4

1. Small, disc-shaped flattened body
2. 2,000 described species in 3 orders
3. Five articulated, muscular arms
4. Reduced water vascular system
5. Tube feet no locomotary function
6. Unattached and freely mobile
7. Mouth and madreporite/s (when present) on oral surface; no anus

8. Bursae
Open via bursal slits
Gas exchange
Gonads open into burase
Fertilisation internal
egg brooding 

9. Arm spines [can be used for predation]

Question 5

Class Echinoidea

8 points

Answer 5

1. Body discoidal or secondarily bilateral
2. 950 described species in 15 orders
3. Interlocking plates form rigid structure called tests
4. Lack arms
5. Unattached and freely mobile
6. Aristotle’s lantern
7. Siphon to remove excess water [runs beside gut. Removes water from intestine so easier to digest food. More concentrated amount of material into gut inorder to digest]
8. Long intestine for digestion

Question 6

Class Echinoidea

regular urchins vs irregular

Answer 6

1. Regular urchins [round]
   Mouth on lower surface
   Anus mid-aboral
   Discodial
2. Irregular
   Mouth anterior
   Anus posterior
   Secondarily bilateral (or heart shaped) [often burrowers]

Question 7

Class Echinoidea
Aristotle’s lantern
4 points

Answer 7

1. Five large calcareous teeth inside the mouth
2. Strong musculature allow protraction, retraction and grasping of teeth
3. Used to scrap algae and bite macroaglae
4. Structure varies among species

Question 8

Class Holothuroidea

9 points

Answer 8

1. 1700 species in 6 orders
2. Elongated body - bilaterally symmetrical
3. Calcareous skeleton reduced to microscopic ossicles [form ridgidity. Can be used for species identification]
4. Lack arms
5. Unattached and freely mobile
6. Extensive water vascular system
7. Mouth anterior; anus posterior
8. Cuvierian tubules
   Released under stress in certain species
   Used for protection
   Toxic

9 Pearlfish feeds on gonads of holothurians