Benthic means "bottom dwelling".
Foraminifera (forams for short) are single celled protists with a shell. The shell is also refered to as its 'test'. There biology can be very simple and complex considering they can have one or more nuclei. The shell is subdivided into chambers. As the organism grows, it builds new chambers inside its shell.
Their test is made up of
organic compounds (calcite composition)
For example, they attach sand grains or other particles from the ocean substrate with a cement their body excretes.
Benthic Foraminifera have a body substance called "protoplasm". This substance fills the chambers which are connected by openings called "formina".