[5] They are sponges with a soft body that covers a hard, often massive skeleton made of calcium carbonate, either aragonite or calcite[citation needed].

[9][2] Because of many species' long life span (500–1,000 years) it is thought that analysis of the aragonite skeletons of these sponges could extend data regarding ocean temperature, salinity, and other variables farther into the past than has been previously possible.

[2] The earliest Demospongiae fossil was discovered in the lower Cambrian (Series 2, Stage 3; approximately 515 Ma) of the Sirius Passet Biota of North Greenland:[10] this single specimen had a spicule assemblage similar to that found in the subclass Heteroscleromorpha.

[12] The Systema Porifera (2002) book (2 volumes) was the result of a collaboration of 45 researchers from 17 countries led by editors J. N. A. Hooper and R. W. M. van Soest.

[13] This milestone publication provided an updated comprehensive overview of sponge systematics, the largest revision of this group (from genera, subfamilies, families, suborders, orders and class) since the start of spongiology in the mid-19th century.

Hooper and van Soest (2002) gave the following classification of demosponges into orders: However, molecular and morphological evidence show that the Homoscleromorpha do not belong in this class.

[14] Morrow & Cárdenas (2015)[15] propose a revision of the Demospongiae higher taxa classification, essentially based on molecular data of the last ten years.

They retain seven (Agelasida, Chondrosiida, Dendroceratida, Dictyoceratida, Haplosclerida, Poecilosclerida, Verongiida) of the 13 orders from Systema Porifera.

They recommend to resurrect or upgrade six order names (Axinellida, Merliida, Spongillida, Sphaerocladina, Suberitida, Tetractinellida).

Fossil chaetetid hyper-calcified demosponges can only be classified with information on their spicule forms and the original mineralogy of their skeletons (West, 2011).

In a favorable situation, an opening called the micropyle appears and releases amoebocytes, which differentiate into cells of all the other types.

[20] Since porifera are the earliest divergent animals, these findings indicate that the basic toolkit of meiosis and recombination were present early in eukaryote evolution.