Odd creature with tail also includes a tailless variety (8)
I believe the answer is:
platypus
'odd creature with tail' is the definition.
'also includes a tailless variety' is the wordplay.
'also' becomes 'plus' (synonyms).
'includes' indicates putting letters inside.
'tailless' means to remove the last letter.
'variety' becomes 'type' (type is a kind of variety).
'type' with its last letter taken away is 'typ'.
'a'+'typ'='atyp'
'plus' going around 'atyp' is 'PLATYPUS'.
(Other definitions for platypus that I've seen before include "Egg-laying mammal" , "Unusual Australian" , "One's billed in flat manner" , "Australian mammal with large bill and webbed feet" , "Australian resident" .)