Define/Explain: Bioluminescence.

In Ctenophora,the body bears $....$ external rows of ciliated comb plates,which help in locomotion.

The ciliated comb plates in $Pleurobrachia$ are meant for

Name an animal that exhibits the phenomenon of bioluminescence and mention the phylum to which it belongs.

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.

Biradial symmetry and lack of cnidoblasts are the characteristics of