Animal designed to leap across delta (7)
I believe the answer is:
tadpole
'animal' is the definition.
(tadpole is a kind of animal)
'designed to leap across delta' is the wordplay.
'designed' is an anagram indicator (designed with the letters).
'across' means one lot of letters goes inside another.
'delta' becomes 'd' (phonetic alphabet: alpha, bravo, charlie etc.).
'to'+'leap'='toleap'
'toleap' is an anagram of 'tapole'.
'tapole' placed around 'd' is 'TADPOLE'.
(Other definitions for tadpole that I've seen before include "Young toad" , "Immature amphibian" , "Amphibian larva" , "Larval form" , "Larval toad" .)