Sea monster you know conceals a wrecked ark (6)
I believe the answer is:
kraken
'sea monster you' is the definition.
The definition suggests a singular noun which matches the answer.
'know conceals a wrecked ark' is the wordplay.
'know' becomes 'ken' (I've seen this in other clues).
'conceals' indicates putting letters inside.
'a wrecked' indicates anagramming the letters.
'ark' anagrammed gives 'rak'.
'ken' placed around 'rak' is 'KRAKEN'.
Can you help me to learn more?
(Other definitions for kraken that I've seen before include "Mythical sea monster (Norway)" , "Legendary monster of Norwegian seas" , "Sea monster that sleepeth (Tennyson)" , "A legendary sea monster of Norwegian myth" , "The -- Wakes (John Wyndham)" .)