Hexactinellid sponges are sponges with a skeleton made of four- and/or six-pointed siliceous spicules, often referred to as glass sponges. They are usually classified along with other sponges in the phylum Porifera, but some researchers consider them sufficiently distinct to deserve their own phylum, Symplasma. Some experts believe glass sponges are the longest-lived animals on earth; these scientists tentatively estimate a maximum age of up to 15,000 years.
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.
Sponge reefs are reefs formed by Hexactinellid sponges, which have a skeleton made of silica, and are often referred to as glass sponges. Such reefs are now very rare, and found only in waters off the coast of British Columbia, Washington and southern Alaska. Recently sponge reefs were identified within the strait of Georgia and Howe sound close to Vancouver. Although common in the late Jurassic period, reef-building sponges were believed to have gone extinct during or shortly after the Cretaceous period, until the existing reefs were discovered Queen Charlotte sound in 1987–1988 – hence these sometimes being dubbed living fossils.
Chancelloria is a genus of early animals known from the Middle Cambrian Burgess Shale, the Comley limestone, the Wheeler Shale, the Bright Angel Shale and elsewhere. It is named after Chancellor Peak. It was first described in 1920 by Charles Doolittle Walcott, who regarded them as one of the most primitive groups of sponges. However, they are currently thought to be member of the group Chancelloriidae. 178 specimens of Chancelloria are known from the Greater Phyllopod bed, where they comprise 0.34% of the community.
Palaeophragmodictya is an extinct genus of sponge-grade organisms from the Ediacaran Period. Originally interpreted as a hexactinellid sponge, the organism also bears some coelomate characteristics, including bilateral symmetry.
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.
Protospongia is a genus of Porifera known from the Middle Cambrian Burgess Shale. 102 specimens of Protospongia are known from the Greater Phyllopod bed, where they comprise 0.19% of the community.
Reticulosa is an extinct order of sea sponges in the class Hexactinellida and the subclass Amphidiscophora. Reticulosans were diverse in shape and size, similar to their modern relatives, the amphidiscosidans. Some were smooth and attached to a surface at a flat point, others were polyhedral or ornamented with nodes, many were covered in bristles, and a few were even suspended above the seabed by a rope-like anchor of braided glass spicules.
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.
Euplectellidae is a family of glass sponges (Hexactinellids) belonging to the order Lyssacinosa, first represented in the Ordovician fossil record, substantially older than molecular estimates of the clade's age.
Rossellidae is a family of glass sponges belonging to the order Lyssacinosa. The family has a cosmopolitan distribution and is found at a large range of depths.
Protomonaxonida is an extinct order of sea sponges. It is a paraphyletic group gathering the most ancient species from the Burgess Shale to modern sponges.
Sceptrulophora is an order of hexactinellid sponges, commonly known as Glass sponges, characterized by sceptrule spicules, that is, "microscleric monactinal triaxonic spicules that include clavules with terminel umbels or smooth heads." Species of the order Sceptrulophora have existed since the Jurassic period, and still flourish today. While there is ongoing debate about the organization of various taxa in Sceptrulophora, the monophyly of the taxon Sceptrulophora is supported by the presence of sceptrules in most of the extant species, and has recently been further supported by DNA sequencing.
Farreidae is a family of glass sponges in the order Sceptrulophora.
Aphrocallistidae is a family of hexactinellid sponges in the order Sceptrulophora.
Claviscopulia is a genus of glass sponge in the family Farreidae.
Bolosoma is a genus of pedunculated siliceous sponges belonging to the family Euplectellidae. This genus lives in deep-sea environments and provides a habitat for a plethora of other benthic species, giving Bolosoma an incredibly important ecological role in the ecosystems it is a part of.
Diapleuridae is a family of five extinct species of marine glass sponges found in the Caribbean Sea, Florida Straits, Banda Sea, and US Virgin Islands. A sixth species–Diapleura hatoni–is postulated to have existed around the same time as the other five, but there is limited research on it. Diapleuridae is part of class Hexactinellida and order Lyssacinosida. These sponges lived during the Middle Epoch of the Eocene and were filter feeders that were attached to the benthos by a basal disc. The oldest recorded fossil of a species of Diapluridae is from 47.8 million years ago, with the most recent fossil dated 41.3 million years ago.
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.
Hemidiscellidae is an extinct family of sponges in the class Hexactinellida and the subclass Amphidiscophora. Hemidiscellidae is the only family in the order Hemidiscosa.
