The calcareoussponges are members of the animal phylum Porifera, the cellular sponges. They are characterized by spicules made of calcium carbonate, in the form of high-magnesium calcite or aragonite. While the spicules in most species are triradiate, some species may possess two- or four-pointed spicules. Unlike other sponges, calcareans lack microscleres, tiny spicules which reinforce the flesh. In addition, their spicules develop from the outside-in, mineralizing within a hollow organic sheath.
Demosponges (Demospongiae) are the most diverse class in the phylum Porifera. They include greater than 90% of all species of sponges with nearly 8,800 species worldwide. They are sponges with a soft body that covers a hard, often massive skeleton made of calcium carbonate, either aragonite or calcite. They are predominantly leuconoid in structure. Their "skeletons" are made of spicules consisting of fibers of the protein spongin, the mineral silica, or both. Where spicules of silica are present, they have a different shape from those in the otherwise similar glass sponges. Some species, in particular from the Antarctic, obtain the silica for spicule building from the ingestion of siliceous diatoms.
Minchinellidae is a family of calcareous sponges, members of the class Calcarea. It is the only family in the monotypic order Lithonida. The families Petrobionidae and Lepidoleuconidae have also sometimes been placed within Lithonida, though more recently they have been moved to the order Baerida. Thanks to their hypercalcified structure, minchinellids have a fossil record reaching as far back as the Jurassic Period.
Baerida is an order of sea sponges in the subclass of Calcaronea, first described in 2000 by Radovan Borojevic, Nicole Boury-Esnault and Jean Vacelet. Baerida contains four families; two of these families were formerly placed within the order Lithonida.
Hexasterophora are a subclass of glass sponges in the class Hexactinellida. Most living hexasterophorans can be divided into three orders: Lyssacinosida, Lychniscosida, and Sceptrulophora. Like other glass sponges, hexasterophorans have skeletons composed of overlapping six-rayed spicules. In addition, they can be characterized by the presence of hexasters, a type of microsclere with six rays unfurling into multi-branched structures.
Lyssacinosida is an order of glass sponges (Hexactinellida) belonging to the subclass Hexasterophora. These sponges can be recognized by their parenchymal spicules usually being unconnected, unlike in other sponges in the subclass where the spicules form a more or less tightly connected skeleton. Lyssacine sponges have existed since the Upper Ordovician, and three families are still alive today. The Venus' flower basket is one of the most well-known and culturally significant of the glass sponges.
Spicules are structural elements found in most sponges. The meshing of many spicules serves as the sponge's skeleton and thus it provides structural support and potentially defense against predators.
Ascute asconoides is a species of calcareous sponge found in Australia.
Ascute uteoides is a species of calcareous sponge found in Australia.
Heteractinida is an extinct grade of Paleozoic (Cambrian–Permian) sponges, sometimes used as a class or order. They are most commonly considered paraphyletic with respect to Calcarea, though some studies instead argue that they are paraphyletic relative to Hexactinellida. Heteractinids can be distinguished by their six-pronged (snowflake-shaped) spicules, whose symmetry historically suggested a relationship with the triradial calcarean sponges.
Baeriidae is a family of calcareous sponges in the class Calcarea. It was named by Borojevic, Boury-Esnault, and Vacelet in 2000. The type genus is BaeriaMiklucho-Maclay, 1870, by original designation, though Baeria is now considered a junior synonym of LeuconiaGrant, 1833.
Trichogypsiidae is a family of sponges in the class Calcarea.
Soleneiscus is a genus of calcareous sponges in the family Dendyidae.
Leuclathrina is a genus of sponges belonging to the family Dendyidae. Species are found in the northeast Atlantic and in the Indian Ocean.
Leucettusa is a genus of sponges belonging to the family Leucaltidae. The species of this genus are mostly known from the Arctic and Antarctic, New Zealand and Southwest Australia.
Coelosphaeridae is a family of sponges belonging to the order Poecilosclerida. Species are found across the globe.
Lychniscosida is an order of sponges belonging to the class Hexactinellida and subclass Hexasterophora. They are dictyonal sponges characterized by the presence of additional struts at the nodes of the skeleton. These struts create octahedral frames, known as lychniscs ("lanterns").
Acarnus is a genus of sponges belonging to the family Acarnidae. The genus has almost cosmopolitan distribution.
Stellispongiida is an order of calcareous sponges, most or all of which are extinct. Stellispongiids are one of several unrelated sponge groups described as "inozoans", a name referring to sponges with a hypermineralized calcitic skeleton independent from their spicules. Stellispongiids have a solid skeleton encasing calcite spicules arranged in trabeculae. "Inozoans" and the similar "sphinctozoans" were historically grouped together in the polyphyletic order Pharetronida.
