Designers who record the numbers of pens for certain animals (8)
I believe the answer is:
stylists
'designers who record the numbers' is the definition.
I can't tell whether this definition defines the answer.
'pens for certain animals' is the wordplay.
'pens' becomes 'styli' (I've seen this in another clue).
'for' says to put letters next to each other.
'certain animals' becomes 'sts' (I can't justify this - if you can you should believe this answer much more).
'styli'+'sts'='STYLISTS'
'of' is the link.
Can you help me to learn more?
(Other definitions for stylists that I've seen before include "Creative hairdressers" , "Hairdressers or designers, very fashionable" .)