Demosponges (Demospongiae) are the most diverse

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently ...

in the

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature ...

Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

. They include 76.2% of all species of

sponges Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

with nearly 8,800 species worldwide (World Porifera Database). They are

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate throu ...

s with a soft body that covers a hard, often massive skeleton made of calcium carbonate, either

aragonite Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...

. They are predominantly leuconoid in structure. Their "

skeletons A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure insid ...

" are made of spicules consisting of fibers of the protein

spongin Spongin, a modified type of collagen protein, forms the fibrous skeleton of most organisms among the phylum Porifera, the sponges. It is secreted by sponge cells known as spongocytes. Spongin gives a sponge its flexibility. True spongin is found ...

, the mineral

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

, 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 A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

. The many diverse

orders Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

in this class include all of the large sponges. Most are marine dwellers, but one order (

Spongillida Spongillida is an order of freshwater sponges Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores an ...

) live in freshwater environments. Some species are brightly colored, with great variety in body shape; the largest species are over across. They reproduce both sexually and asexually. They are the only extant organisms that

methylate In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These ...

sterol Sterol is an organic compound with formula , whose molecule is derived from that of gonane by replacement of a hydrogen atom in position 3 by a hydroxyl group. It is therefore an alcohol of gonane. More generally, any compounds that contain the go ...

s at the 26-position, a fact used to identify the presence of demosponges before their first known unambiguous fossils. Because of many species' long life span (500–1,000 years) it is thought that analysis of the aragonite

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

s of these sponges could extend data regarding

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wor ...

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

, and other variables farther into the past than has been previously possible. Their dense skeletons are deposited in an organized chronological manner, in concentric layers or bands. The layered skeletons look similar to

reef A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes—deposition of sand, wave erosion planing down rock ...

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and se ...

s. Therefore, demosponges are also called coralline sponges.

Classification and systematics

The Demospongiae have an ancient history. The first demosponges may have appeared during the

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of th ...

deposits at the end of the

Cryogenian The Cryogenian (from grc, κρύος, krýos, meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed ...

"Snowball Earth" period. Their presence has been indirectly detected by fossilized steroids, called

sterane Sterane (cyclopentanoperhydrophenanthrenes) compounds are a class of tetracyclic compounds derived from steroids or sterols via diagenetic and catagenetic degradation and saturation. Steranes have an androstane skeleton with a side chain at carb ...

s, hydrocarbon markers characteristic of the cell membranes of the sponges, rather than from direct fossils of the sponges themselves. They represent a continuous chemical fossil record of demosponges through the end of the

Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is prec ...

. The earliest Demospongiae fossil was discovered in the lower

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...

(Series 2, Stage 3; approximately 515 Ma) of the

Sirius Passet Sirius Passet is a Cambrian Lagerstätte in Peary Land, Greenland. The Sirius Passet Lagerstätte was named after the Sirius sledge patrol that operates in North Greenland. It comprises six places in Nansen Land, on the east shore of J.P. Koch F ...

Biota of North Greenland: this single specimen had a spicule assemblage similar to that found in the subclass

Heteroscleromorpha Heteroscleromorpha is a subclass of demosponges within the phylum Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms th ...

. The earliest sponge-bearing

s date to the Early Cambrian (they are the earliest known reef structure built by animals), exemplified by a small bioherm constructed by archaeocyathids and calcified microbes at the start of the Tommotian stage about 530 Ma, found in southeast Siberia. A major radiation occurred in the Lower

and further major radiations in the

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

possibly from the middle Cambrian. 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. This milestone publication provided an updated comprehensive overview of sponge

systematics Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic t ...

, the largest revision of this group (from genera, subfamilies, families, suborders, orders and class) since the start of spongiology in the mid-19th century. In this large revision, the extant Demospongiae were organized into 14 orders that encompassed 88 families and 500 genera. Hooper and van Soest (2002) gave the following classification of demosponges into orders: * Subclass

Homoscleromorpha Homosclerophorida is an order of marine sponges. It is the only order in the monotypic class Homoscleromorpha. The order is composed of two families: Plakinidae and Oscarellidae. Taxonomy Homoscleromorpha is phylogenetically well separated fr ...

Bergquist 1978 **

Homosclerophorida Homosclerophorida is an order of marine sponges. It is the only order in the monotypic class Homoscleromorpha. The order is composed of two families: Plakinidae and Oscarellidae. Taxonomy Homoscleromorpha is phylogenetically well separated from ...

Dendy 1905 * Subclass

Tetractinomorpha Heteroscleromorpha is a subclass of demosponges within the phylum Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms th ...

** Astrophorida Sollas 1888 ** Chondrosida Boury-Esnault & Lopès 1985 **

Hadromerida Heteroscleromorpha is a subclass of demosponges within the phylum Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms th ...

Topsent 1894 **

Lithistida Heteroscleromorpha is a subclass of demosponges within the phylum Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms tha ...

Sollas 1888 **

Spirophorida ''Spirophorina'' is a suborder of sea sponges belonging to the class Demospongiae Demosponges (Demospongiae) are the most diverse class in the phylum Porifera. They include 76.2% of all species of sponges with nearly 8,800 species world ...

Bergquist & Hogg 1969 * Subclass

Ceractinomorpha Demosponges (Demospongiae) are the most diverse class in the phylum Porifera. They include 76.2% of all species of sponges with nearly 8,800 species worldwide (World Porifera Database). They are sponges with a soft body that covers a hard, ...

Lévi 1953 **

Agelasida Agelasida is an order of sea sponges in the class Demospongiae Demosponges (Demospongiae) are the most diverse class in the phylum Porifera. They include 76.2% of all species of sponges with nearly 8,800 species worldwide (World Porifer ...

Verrill 1907 **

Dendroceratida Dendroceratida is an order of sponges of the class Demospongiae. They are typically found in shallow coastal and tidal areas of most coasts around the world. They are generally characterized by concentric layers of fibers containing spongin (a ...

Minchin 1900 **

Dictyoceratida Dictyoceratida is an order of sponges in the subclass Ceractinomorpha containing five families. Along with the Dendroceratida, it is one of the two orders of demosponges that make up the keratose or "horny" sponges, in which a mineral skeleton ...

Minchin 1900 **

Halichondrida Heteroscleromorpha is a subclass of demosponge Demosponges (Demospongiae) are the most diverse class in the phylum Porifera. They include 76.2% of all species of sponges with nearly 8,800 species worldwide (World Porifera Database). ...

Gray 1867 ** Halisarcida Bergquist 1996 ** Haplosclerida Topsent 1928 **

Poecilosclerida Poecilosclerida is an order of the demosponge class. It is the most speciose demosponge order with over 2200 species (World Porifera Database). It contains about 25 recognised families. They are characterised by having chelae microscleres, that ...

Topsent 1928 ** Verongida Bergquist 1978 ** Verticillitida Termier & Termier 1977 However, molecular and morphological evidence show that the

do not belong in this class. The

was therefore officially taken out of the Demospongiae in 2012, and became the fourth class of phylum Porifera. Morrow & Cárdenas (2015) propose a revision of the Demospongiae higher taxa classification, essentially based on molecular data of the last ten years. Some demosponge subclasses and orders are actually

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

or should be included in other orders, so that Morrow and Cárdenas (2015) officially propose to abandon certain names: these are the

, Halisarcida, Verticillitida,

and

. Instead, they recommend the use of three subclasses:

Verongimorpha Verongimorpha is the name of a subclass of sea sponges within the phylum Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organ ...

Keratosa Keratosa, the keratose sponges or horny sponges, is a subclass of demosponge Demosponges (Demospongiae) are the most diverse class in the phylum Porifera. They include 76.2% of all species of sponges with nearly 8,800 species worldwid ...

and

. They retain seven (

, Chondrosiida,

, Haplosclerida,

, Verongiida) of the 13 orders from Systema Porifera. They recommend to resurrect or upgrade six order names (

Axinellida Axinellida is an order of demosponges in the subclass Heteroscleromorpha Heteroscleromorpha is a subclass of demosponges within the phylum Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal anima ...

, Merliida,

Sphaerocladina ''Vetulina'' is a genus of sea sponges in the subclass Heteroscleromorpha Heteroscleromorpha is a subclass of demosponges within the phylum Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal ani ...

Suberitida Suberitida is an order of sponges belonging to the class Demospongiae. Families: * Halichondriidae * Stylocordylidae * Suberitidae Suberitidae is a family of sea sponges Sponges, the members of the phylum Porifera (; meaning 'pore bear ...

, Tetractinellida). Finally, they create seven new orders ( Bubarida, Desmacellida,

Polymastiida Polymastiidae is a family of demosponges found in oceans throughout the world. It is the only family in the monotypic order Polymastiida. A useful diagnostic characteristic of members of this family is the presence of numerous surface papilla P ...

Scopalinida Scopalinidae is an family of demosponges in the subclass Heteroscleromorpha Heteroscleromorpha is a subclass of demosponges within the phylum Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal an ...

, Clionaida,

Tethyida Tethyida is an order of sea sponges in the subclass Heteroscleromorpha Heteroscleromorpha is a subclass of demosponges within the phylum Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal ...

Trachycladida Trachycladidae is a family of sea sponges in the subclass Heteroscleromorpha Heteroscleromorpha is a subclass of demosponges within the phylum Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal ...

). These added to the recently created orders (

Biemnida Biemnida is an order of demosponges in the subclass Heteroscleromorpha Heteroscleromorpha is a subclass of demosponges within the phylum Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal ...

and Chondrillida) make a total of 22 orders in the revised classification. These changes are now implemented in the World Porifera Database part of the World Register of Marine Species. * Subclass

Cárdenas, Pérez, Boury-Esnault, 2012 ** order

Verrill, 1907 ** order

Lévi, 1953 ** order

Morrow et al., 2013 ** order Bubarida Morrow & Cárdenas, 2015 ** order Clionaida Morrow & Cárdenas, 2015 ** order Desmacellida Morrow & Cárdenas, 2015 ** order Haplosclerida Topsent, 1928 ** order Merliida Vacelet, 1979 ** order

Topsent, 1928 ** order

Morrow & Cárdenas, 2015 ** order

Schrammen, 1924 ** order

Manconi & Pronzato, 2002 ** order

Chombard & Boury-Esnault, 1999 ** order

Morrow & Cárdenas, 2015 ** order Tetractinellida Marshall, 1876 ** order

Morrow & Cárdenas, 2015 ** Heteroscleromorpha incertae sedis * Subclass

Erpenbeck et al., 2012 ** order Chondrillida Redmond et al., 2013 ** order Chondrosiida Boury-Esnault et Lopès, 1985 ** order Verongiida Bergquist, 1978 * Subclass

Grant, 1861 ** order

Minchin, 1900 ** order

Minchin, 1900

Sclerosponges

Sclerosponges were first proposed as a class of sponges, Sclerospongiae, in 1970 by Hartman and Goreau. However, it was later found by Vacelet that sclerosponges occur in different classes of

. That means that sclerosponges are not a closely related ( taxonomic) group of sponges and are considered to be a polyphyletic grouping and contained within the Demospongiae. Like bats and

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s that independently developed the ability to fly, different sponges developed the ability to build a calcareous skeleton independently and at different times in Earth's history. Fossil sclerosponges are already known from the

period.

Chaetetids

Chaetetids, more formally called "chaetetid hyper-calcified demosponges" (West, 2011), are common calcareous

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

composed of fused tubules. They were previously classified as extinct

corals Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...

bryozoans Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a l ...

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

, stromatoporoids and sclerosponges. The chaetetid skeleton has now been shown to be of polyphyletic origin and with little systematic value. Extant chaetetids are also described. This skeleton is now known from three demosponge orders (Hadromerida, Poecilosclerida, and Agelasida). Fossil chaetetid hyper-calcified demosponges can only be classified with information on their spicule forms and the original mineralogy of their skeletons (West, 2011). File:Chaetetid Bird Spring Upper Carboniferous Nevada.jpg, Fossil chaetetid from the

Bird Spring Formation The Bird Spring Formation is a geologic formation in Nevada. It preserves fossils dating back to the Carboniferous and Permian periods. See also * List of fossiliferous stratigraphic units in Nevada * Paleontology in Nevada Paleontology in N ...

( Upper Carboniferous) of southern

Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...

. File: Chaetetid Bird Spring cross-section Upper Carboniferous Nevada.jpg, Cross-section of a fossil chaetetid (Bird Spring Formation, Upper Carboniferous, Nevada.

Reproduction

Spermatocytes develop from the transformation of choanocytes and

oocytes An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female g ...

arise from archeocytes. Repeated cleavage of the zygote egg takes place in the

mesohyl The mesohyl, formerly known as mesenchyme or as mesoglea, is the gelatinous matrix within a sponge. It fills the space between the external pinacoderm and the internal choanoderm. The mesohyl resembles a type of connective tissue and contains s ...

and forms a

parenchymella Parenchymella is a type of larva of a demosponge Demosponges (Demospongiae) are the most diverse class in the phylum Porifera. They include 76.2% of all species of sponges with nearly 8,800 species worldwide (World Porifera Database). The ...

larva with a mass of larger internal cells surrounded by small, externally

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have fro ...

ted cells. The resulting swimming larva enters a canal of the central cavity and is expelled with the exhalant current. Methods of asexual reproduction include both budding and the formation of gemmules. In budding, aggregates of cells differentiate into small sponges that are released superficially or expelled through the oscula. Gemmules are found in the freshwater family

Spongillidae Spongilidae is a family of sponges that live in freshwater lakes and rivers. The following genera are recognized in the family: * '' Anheteromeyenia'' Schröder, 1927 * '' Corvoheteromeyenia'' Ezcurra de Drago, 1979 * '' Corvospongilla'' Annanda ...

. They are produced in the mesohyl as clumps of archeocytes, are surrounded with a hard layer secreted by other amoebocytes. Gemmules are released when the parent body breaks down, and are capable of surviving harsh conditions. In a favorable situation, an opening called the micropyle appears and releases amoebocytes, which differentiate into cells of all the other types.

Economic importance

The most economically important group of demospongians to human are the bath sponges. These are harvested by divers and can also be grown commercially. They are bleached and marketed; the

gives the sponge its softness.

Citations

# #

General references

* Barnes, R. S. K. et al. (2001). ''The Invertebrates: A Synthesis''. Oxford: Blackwell Science. . * Bergquist, P. R. ''Sponges''. Berkeley, CA: University of California Press; 1978. pp. 86–103. * Hickman, C. P. ''Biology of the Invertebrates''. Saint Louis, MO: C. V. Mosely Publishing. * Kozloff, E. N. ''Invertebrates''. Philadelphia, PA: Saunders College Publishing; 1990. pp. 74–91. * * Reitner, J. and D. Mehl. 1996. Monophyly of the Porifera. Verhandlungen des Naturwissenschaftlichen Vereins in Hamburg. 36: 5–32. * West, R. R. 2011. Part E, Revised, Volume 4, Chapter 2A: "Introduction to the fossil hypercalcified chaetetid-type Porifera (Demospongiae)". Treatise Online 20: 1–79. {{Taxonbar, from=Q248530 Cryogenian first appearances