Penetrantiidae

Colony boring into the shells of molluscs, comprising a kenozooidal stolon of short identical units, budding pedunculate autozooids orientated perpendicularly to the substratum surface. Peduncle situated at distal end of zooid. Autozooid with doubled cuticular body wall; orifice terminal, closed by an operculum. Embryos brooded singly within the body cavity of specialised gonozooids.

(Hayward, 1985)