Deep-sea sponge research has historically been biased towards the largest, most conspicuous species, while small and inconspicuous forms have received considerably less attention. Moreover, these small sponges were often regarded just as immature or initial growth stages of the formers. However, recent studies have demonstrated that many of these miniaturized forms are, in fact, fully developed, distinct species, worthy of detailed investigation. Through integrative taxonomy, and building upon newly collected material and prior research conducted over the past decade, a new family, Spinulariidae fam. nov., is here proposed within the order Polymastiida in order to encompass deep-sea polymastiid genera lacking a secondary layer of tangential megascleres in their cortex. This new family, built on Spinularia Gray, 1867, is also supported by all phylogenetic analyses, with additional molecular and/or morphological evidence supporting the inclusion of Radiella Schmidt, 1870, Atergia Stephens, 1915, Tylexocladus Topsent, 1898, Astrotylus Plotkin & Janussen, 2007, Acanthopolymastia Kelly-Borges & Bergquist, 1997, Pseudotrachya Hallmann, 1914 and Tentorium Vosmaer, 1887 into the family. Still, the boundaries among these genera remain uncertain, as all exhibit high levels of polyphyly across all the molecular markers analysed. Most of these genera are currently distinguished by the presence or absence of particular microscleres, yet these traits appear to be homoplastic and lack diagnostic value above the species level. Therefore, until further data arises it is also proposed here to synonymize Radiella, Atergia, Tylexocladus and Astrotylus with Spinularia, but keeping them as subgenera. This study highlights the importance of giving taxonomic attention to small inconspicuous specimens, which despite being challenging and time-consuming to study, can hold significant evolutionary and systematic insights.