The Slit worm shell above is actually a snail with a typical snail body, not a worm and can be found in the Mediterranean and down the West African coast. The shell is often mistaken for the casing of a polychaete worm. A slit or series of holes runs down the length of the shell, and this may or may not be closed by a thin layer of shell.
Slit worms lead fairly sedentary lives often living among sponges with only the open end protruding into the water.
The West Indian worm shell, above, can be found from the Caribbean to the North Atlantic, down to around 400 m deep, and often embedded in sponges.
Carrier shell, Xenophora corrugata, above is found in South East Asia.
The Pallid carrier shell, below, is found in deep waters, around 200 - 960 m deep, in the Indo-Pacific. Xeno is Latin for foreign, and this gives the snail its name as it cements objects to its shell, and as the shell grows the objects become embedded. Often the objects will be other snail shells that are uninhabited, these will be attached by the pointed end. Clam shells are also attached as well as stones, glass sponges, corals, etc. The snail takes great care in positioning an object for attachment, and will spend around 2 hours getting it just right, then it waits another 10 hours for the cement to harden. During this time the snail stays still. Without attachments the snail ranges from 19 - 90 cm in diameter and 21 - 60 in height.
The attached items provide camouflage and also as they stick out they form a sort of cage allowing the snail to graze freely on algae.
These snails have another curious behaviour. They dig a hole in the sediment and bury their faeces.