ST Cryptic 2484

[Four Clubs]

Could you help me with a few clues, please.
5dn Tense, as pupil is in audition (4ltrs) t--t I think it might be tort, but not sure.
16dn Marine crustacean exposed, retaining salt (8lts)
b-r-a--- Again I think it could be barnacle but cannot see why!
27ac British citizen, fellow taken in by recluse (8ltrs)
--n--n-r
9ac Scary attitude in hospital - arm is mistreated --a--i-m
Many thanks.
Four Clubs

[dr b]

5, taut (sounds like taught)

16 bar(nacl)e, NACL = salt (sodium chloride)

[grasscarp]

exposed is bare, and salt is sodium chloride NaCl

[dr b]

27, Lon(don)er

[piggling]

9 al arm is m

[Four Clubs]

Many thanks to you all. I can now get some sleep.
Good night.
Four Clubs.