What is the function of the comb plates present in Ctenophora?

Identify the phylum which shows the following characteristics:
$1$. Animals are exclusively marine,radially symmetrical,and diploblastic.
$2$. Body bears eight external rows of ciliated comb plates which help in locomotion.
$3$. Digestion is both extracellular and intracellular.
$4$. Reproduction is only by sexual means.

Ctenophoras are exclusively marine,$X$,$Y$ organisms with tissue level of organisation.
$X$ - $Y$

Why is $Ctenophora$ considered a minor phylum?

Bioluminescence is a characteristic of which phylum?

Define/Explain: Bioluminescence.