Shell of molluscs is derived from
foot
mantle
ctenidia
placoid
B.
mantle
Molluscs are the soft bodied, unsegmented animals covered by a shell. Mantle is the dorsal body wall which covers the organs of digestion, reproduction and movement. In between the shell and body wall is a covering called mantle, which secretes the shell.
Moulting hormone is secreted by
corpora cardacum
corpora allata
neurosecretory hormone
prothoracic gland