a) 19A Cad, in other words, gets rid of cleaner and returns to his place in the Indian Ocean (5).
Answer seems to be Natal - apart from Indian Ocean connection why?
b) 40A It's the turn of the plant that gets under a sailor's feet (4)
Answer: -EE-
c) 16D Being firm, and big, settles in very snugly (7).
Answer: N-s-l-s
Seems to be "nestles" but can't figure connection to being firm and big.