Solenogastres

The Solenogasres are a small class of shell-less molluscs which gnerally live on the surface of cnidarians such as hydroids and corals. In some cases the species a particular species of Solenogastres is associated with appears to be very specific. They are an entirely marine group occuring to considerable depths but rarely found in water less than 20m deep. 

They feed mainly on their cnidarian hosts and nematocysts (a special sort of cell found in cnidarians) are regularly found in the guts of Solenogastres. Where a radula is present (not all species possess one) it is used to break up the food before it is ingested.

The group does not possess gills though some species have evolved other respiratory structures. Instead oxygen is extracted from the water across the surface of the mantle cavity (which is known as a cloaca in this group).

The group are hermaphrodites but it thought that breeding generally involve copulation and cross fertilizaton. Several workers have reported  two individuals curled around each other with the mantle cavities in contact which is assumed to be evidence of copulation. The larval stage is poorly described but is thought to involve a planktonic stage.