Spiny thing moved inches across back of bayou (7)

I believe the answer is:

echinus

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'spiny thing' is the definition.
The definition suggests a singular noun which matches the answer.

'moved inches across back of bayou' is the wordplay.
'moved' indicates an anagram.
'across' is an insertion indicator.
'back of' indicates one should take the final letters.
The last letter of 'bayou' is 'u'.
'inches' is an anagram of 'echins'.
'echins' enclosing 'u' is 'ECHINUS'.

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(Other definitions for echinus that I've seen before include "Sea creature" , "Marine creature" , "Urchin" .)

I've seen this clue in The Independent.

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