|
|
|
|
Tubes made by snails such as vermetids are glossy on the inside because
of a deposit of nacre (mother-of-pearl), and made up of three layers. |
Tubes
made by worms such as keelworms are dull on the inside and made up
of two layers. |
|
|
Vermetid
snails don't have a feathery fan on their heads. They collect food
by secreting a net of mucus. |
Keelworms
have a feathery fan on their heads. This is extended when they are
submerged to filter edible bits. |