Question

Phylum Echinodermata                     

1. starfish dissection

        Starfish external structure examination

Identify:

1. Oral surface

Mouth

Tube feet

Ambulacral groove

2. Aboral surface

Arm

Spines

Central disk

Madreporite

2. List examples for the following classes.

1. Class Asteroidea

2. Class Ophiuroidea

3. Class Crinoidea

4. Class Echinoidea

5. Class Holothuroidea

Answer 1

Ans.1) The lower surface of the body kept towards the substraum is flat and called oral surface.

The upper surface of body is convex and is called aboral surface.

a)oral surface -

• Mouth - circular aperture at the top of 5-rayed depression at the center of the oral surface of the central side. The depression is known as Actinostome. The mouth is surrounded by a tough,muscular membrane called Peristomial membrane.
• Ambulacral groove - are five narrow channels that radiate out from the angles of the actinostome, one extending along the middle of oral surface of each arm up to its top.
• Tube feet - are short, tubular processes arranged in four radial rows in each ambulacral groove. Each tube ends in a sucker.

b) Aboral surface-

• central disc- the body consists of a 5-sided central part, called central disc.
• Arm- 5 arms radiates from the center and are symmetrical arranged. Arms slightly taper toward their distal free ends.
• spines- are short, stout out growths from calcareous plates.they are embedded in the body wall and covered by epidermis. Spines of aboral surface are whitish and immovable. They occur in irregular radial rows.
• Maderoprite - flat, subcircular plate situated on the aboral surface of central disc in one of the inter radii close to the base of 2 arms.Its surface is marked by a no. of radiating, narrow, straight or wavy grooves with pores in them. The two arms having maderoprite between their bases are called Bivium, and other three are called Trivium.

​​​​​​​Ans.2) a) Class Asteroidea- Oreaster, Asteropacten, Solaster, Asterias.

class ophiuroidea - Ophioderma, Ophiothrix, Astrophyton

class crinoidea - Antedon.

class echinoidea - Echinus, Strongylocentrotus.

class holothuroidea - Cucumaria, Thyone.