Pachastrellidae Carter (Demospongiae: Astrophorida), including Theneidae Carter, contains 12 valid genera and 2 subgenera. Most genera contain cup-like, massive, and submassive species and are distributed from tropical to high latitudes, mostly in epibathyal and bathyal
habitats. A few genera also include encrusting or cavity-filling forms found predominantly in tropical or temperate shallow-water habitats. This astrophorid family is defined by the possession of tetraxons (calthrops, short-shafted triaenes, mesotriaene-derived desmas, or longshafted triaenes) in combination with streptasters (never euasters) and in most cases by monaxonic microscleres (Le., microxeas, microstyles and microstrongyles). The microscleres are densely packed at the ectosome forming a feltwork. The relationship between genera possessing a typical pachastrellid skeleton and some genera bearing tetraxial desmas other than mesotriaene-derived desmas (mesotriders), which have traditional been included in Lithistida, is still a matter of contention.