Marine species lookin' to catch you, ultimately (3,6)
I believe the answer is:
sea urchin
'marine species' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'lookin' to catch you ultimately' is the wordplay.
I cannot really understand how this works, but
'you' could be 'u' (commonly used in online communication) and 'u' is located in the answer.
'lookin'' could be 'searchin' ('searching' pronounced like 'looking' was; 'search' can be a synonym of 'look') and 'searchin' is found within the leftover letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sea urchin that I've seen before include "Echinoderm with a thin spiny globular shell" , "A problem for barefoot dabblers" , "Main thing" , "Marine creature with near-spherical spiny shell" , "Marine invertebrate with spikes" .)