Spicules of silica occur in

Which one of the following statements about all the four of $Spongilla$,leech,dolphin and penguin is correct?

The most distinctive character of sponges is:

In $Poriferans$,the skeleton is made up of

$S$ - Statement: $Leucosolenia$ is an animal belonging to the phylum Porifera.
$R$ - Reason: Animals in this phylum are multicellular and possess a porous body.

Which is the simplest canal system in Porifera?