Modern ice melting, penetrated by hot sea creature (10)
I believe the answer is:
echinoderm
'sea creature' is the definition.
(I've seen this before)
'modern ice melting penetrated by hot' is the wordplay.
'melting' indicates an anagram.
'penetrated by' is an insertion indicator (I've seen this in other clues).
'hot' becomes 'h' (abbreviation eg on taps).
'modern'+'ice'='modernice'
'modernice' is an anagram of 'ecinoderm'.
'ecinoderm' enclosing 'h' is 'ECHINODERM'.
(Other definitions for echinoderm that I've seen before include "Eg, sea urchin" , "sea creature" , "Maybe urchin" .)