a. What is biradial symmetry
In bilateral symmetry (also called plane symmetry), only one plane, called the sagittal plane, will divide an organism into roughly mirror image halves. Thus there is approximate reflection symmetry. Often the two halves can meaningfully be referred to as the right and left halves, e.g. in the case of an animal with a main direction of motion in the plane of symmetry.
b. What is axial complex?
In Asterias the stone canal, axial gland and axial sinus together form a complex, which is called axial complex.
c. What is placophora?
A division of gastropod Mollusca, including the chitons. The back is covered by eight shelly plates.
d. What is the larval form of Echinoidea?
The larval form of Echinoidea is Pluteus larva.
a. What is streptoneurous chiastoneury?
In primeval snail groups the two main neural pathways run straight and parallel from front to back. After the torsion, in the prosobranch stage, those nerves are crossed, a situation referred to as chiastoneury, those snail groups thus also called Streptoneura (crossed nerve snails). The prosobranchia (sea snails, land snails, freshwater snails) show streptoneurous chiastoneury.
b. Define Doliolaria larva with characteristic features.
In the individuals of the class Crinoidea development of the embryo leads to the hatching of a Doliolaria (little barrel) larva. This larva possess an apical sensory plate at its anterior end that bears a tuft of cilia. An adhesive pit is present at the anterior end of the body.
c. Function of W.V.S.
The water vascular system in echinoderms helps in locomotion, food and water transportation and respiration.
Q.3> What is W.V.S.
a. The water vascular system is a hydraulic system used by echinoderms, such as starfish and sea urchins, for locomotion, food and waste transportation, and respiration. The system is composed of canals connecting numerous tube feet. Echinoderms move by alternately contracting muscles that force water into the tube feet, causing them to extend and push against the ground, then relaxing to allow the feet to retract