Coelenterate with a skeleton of $CaCO_3$ is called as:

Metagenesis can be seen in

$S$ - Statement: Some species of $Coelenterata$ exhibit polymorphism.
$R$ - Reason: In $Coelenterata$,the medusa form is observed as the asexual stage.

Cnidoblasts are found in .........

Which of the following animals is without a sexual medusa stage?

Obelia is characterised by:
$A$. Ciliated free-swimming planula larva
$B$. Metagenesis
$C$. Acraspedote medusa
$D$. Statocysts present in medusoid stage