A fruiting body is called secotioid when its structure is that of a "normal" mushroom that just never opened (and, often, never totally breaks out of the ground). Both boletes and gilled mushrooms have secotioid forms. A secotioidfruiting body usually looks like a lumpy mass on the outside, and if you cross-section it, you will see a convoluted mass of gills or tubes, and perhaps a stem. Most secotioidfungi occur in desert environments, so this growth habit is thought to be an adaptation that protects the developing spores from the dry climate.
All secotioidfungi used to be placed in one order, the Hymenogastrales; but phylogenetically, they should all really go with the non-secotioid forms that they resemble.
