You cannot add or edit SRS subhabitats or habitats - the whole point of these is to provide a fixed structured system that can be used in analyses such as the summary charts provided on the species pages. Any detail can be added in the comment field/s. You can get more information from the Recording Methodology page.
Within any large area of broad habitat, spiders are generally associated more with structural habitats and hydrological changes, and within a large broad habitat area it may be most sensible to set up smaller blocks with eg different hydrology as separate sites, as long as this is made clear in the site name.
