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 differentl ...

in the phylum Porifera. They include 76.2% of all species of sponges 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 throug ...

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 ...

or calcite. 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 inside ...

" are made of

spicule Spicules are any of various small needle-like anatomical structures occurring in organisms Spicule may also refer to: *Spicule (sponge), small skeletal elements of sea sponges *Spicule (nematode), reproductive structures found in male nematodes ( ...

s 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 (New Latin, 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 com ...

. The many diverse orders in this class include all of the large sponges. Most are marine dwellers, but one order ( Spongillida) 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 sterols 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 skeletons 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 wo ...

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measurement, measured with a thermometer. Thermometers are calibrated in various Conversion of units of temperature, temp ...

, salinity, 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 o ...

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 ...

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 deposits at the end of the Cryogenian "Snowball Earth" period. Their presence has been indirectly detected by fossilized steroids, called steranes, 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 (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

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

archaeocyathid Archaeocyatha (or archaeocyathids 'ancient cups') is a taxon of extinct, sessile, reef-building marine sponges that lived in warm tropical and subtropical waters during the Cambrian Period. It is believed that the centre of the Archaeocyatha or ...

s and calcified microbes at the start of the Tommotian stage about 530 Ma, found in southeast Siberia. A major radiation occurred in the Lower Cambrian 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, 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 Dendy 1905 * Subclass Tetractinomorpha **

Astrophorida Astrophorina is a Order (biology), suborder of sea sponges in the class Demospongiae. Astrophorina was formerly named Astrophorida and classified as an order, but it is now recognised as a suborder of TetractinellidaMorrow & Cárdenas' (2015) rev ...

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 Sollas 1888 ** Spirophorida Bergquist & Hogg 1969 * Subclass Ceractinomorpha Lévi 1953 ** Agelasida Verrill 1907 ** Dendroceratida Minchin 1900 ** Dictyoceratida Minchin 1900 ** Halichondrida Gray 1867 ** Halisarcida Bergquist 1996 **

Haplosclerida Haplosclerida is an order 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). They are ...

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 Ceractinomorpha, Tetractinomorpha, Halisarcida, Verticillitida, Lithistida, Halichondrida and

. Instead, they recommend the use of three subclasses: Verongimorpha,

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 ( Agelasida, Chondrosiida, Dendroceratida, Dictyoceratida,

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

Tetractinellida Tetractinellida is an Order (biology), order of sea sponges belonging to the Class Demospongiae. First described in 1876, this order received a new description in 2012 and replaced the two orders Astrophorida and Spirophorida, which then became s ...

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

Clionaida Clionaida is an order 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). They are spo ...

, Tethyida, Trachycladida). These added to the recently created orders ( Biemnida 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 Agelasida Verrill, 1907 ** order Axinellida Lévi, 1953 ** order Biemnida Morrow et al., 2013 ** order Bubarida Morrow & Cárdenas, 2015 ** order

Morrow & Cárdenas, 2015 ** order Desmacellida Morrow & Cárdenas, 2015 ** order

Topsent, 1928 ** order Merliida Vacelet, 1979 ** order

Topsent, 1928 ** order Polymastiida Morrow & Cárdenas, 2015 ** order Scopalinida Morrow & Cárdenas, 2015 ** order Sphaerocladina Schrammen, 1924 ** order Spongillida Manconi & Pronzato, 2002 ** order Suberitida Chombard & Boury-Esnault, 1999 ** order Tethyida Morrow & Cárdenas, 2015 ** order

Marshall, 1876 ** order Trachycladida Morrow & Cárdenas, 2015 ** Heteroscleromorpha incertae sedis * Subclass Verongimorpha 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 Dendroceratida Minchin, 1900 ** order Dictyoceratida 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 Porifera. 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

bat Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most ...

s 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 The history of Earth concerns the development of planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to understanding of the main events of Earth's past, characterized by constant geologic ...

. Fossil sclerosponges are already known from the Cambrian period.

Chaetetids

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

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, 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 The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years ...

(

Upper Carboniferous Upper may refer to: * Shoe upper or ''vamp'', the part of a shoe on the top of the foot * Stimulant, drugs which induce temporary improvements in either mental or physical function or both * ''Upper'', the original film title for the 2013 found f ...

) of southern

Nevada Nevada ( ; ) is a state in the 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. Nevada is the 7th-most extensive, ...

. 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 Choanocytes (also known as "collar cells") are cells that line the interior of asconoid, syconoid and leuconoid body types of sponges that contain a central flagellum, or ''cilium,'' surrounded by a collar of microvilli which are connected by a ...

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

gemmule Gemmules are internal buds found in sponges and are involved in asexual reproduction. It is an asexually reproduced mass of cells, that is capable of developing into a new organism i.e., an adult sponge. Role in asexual reproduction Asexual ...

s. 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. 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