Demosponges (Demospongiae) are the most diverse class in the phylumPorifera. They include greater than 90% of all species of sponges with nearly 8,800 species worldwide (World Porifera Database).[4] 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.[5] Some species, in particular from the Antarctic, obtain the silica for spicule building from the ingestion of siliceous diatoms.[6]
The many diverse orders in this class include all of the large sponges. About 311 million years ago, in the Late Carboniferous, the order Spongillida split from the marine sponges, and is the only sponges to live in freshwater environments.[7] Some species are brightly colored, with great variety in body shape; the largest species are over 1m (3.3ft) across.[5] They reproduce both sexually and asexually. They are the only extant organisms that methylatesterols at the 26-position, a fact used to identify the presence of demosponges before their first known unambiguous fossils.[8][1]
Because of many species' long life span (500–1,000years) 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. Their dense skeletons are deposited in an organized chronological manner, in concentric layers or bands. The layered skeletons look similar to reefcorals. 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.[1] 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:[9] this single specimen had a spicule assemblage similar to that found in the subclass Heteroscleromorpha. The earliest sponge-bearing reefs 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.[10] A major radiation occurred in the Lower Cambrian and further major radiations in the Ordovician possibly from the middle Cambrian.[11]
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.[12] 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:
However, molecular and morphological evidence show that the Homoscleromorpha do not belong in this class. The Homoscleromorpha was therefore officially taken out of the Demospongiae in 2012, and became the fourth class of phylum Porifera.[13]
Sclerosponges were first proposed as a class of sponges, Sclerospongiae, in 1970 by Hartman and Goreau.[16] However, it was later found by Vacelet that sclerosponges occur in different classes of Porifera.[17] 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 birds 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 Cambrian period.[18]
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, bryozoans, 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).
Spermatocytes develop from the transformation of choanocytes and oocytes arise from archeocytes. Repeated cleavage of the zygote egg takes place in the mesohyl 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 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. 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.
Meiosis and recombination
The cytological progression of poriferaoogenesis and spermatogenesis (gametogenesis) shows great similarity to other metazoa.[19] Most of the genes from the classic set of meiotic genes conserved in eukaryotes are upregulated in the sponges Geodia hentscheli and Geodia phlegraei including genes for DNA recombination.[19] Since porifera are the earliest divergent animals, these findings indicate that the basic toolkit of meiosis and recombination were present early in eukaryote evolution.[19]
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 spongin gives the sponge its softness.
↑ Vacelet, J. (2006). "New carnivorous sponges (Porifera, Poecilosclerida) collected from manned submersibles in the deep Pacific". Zoological Journal of the Linnean Society. 148 (4): 553–584. Figure 17. doi:10.1111/j.1096-3642.2006.00234.x.
↑ Brocks, J. J.; Jarrett, A. J. M.; Sirantoine, E.; Kenig, F.; Moczydłowska, M.; Porter, S.; Hope, J. (2016-03-01). "Early sponges and toxic protists: possible sources of cryostane, an age diagnostic biomarker antedating Sturtian Snowball Earth". Geobiology. 14 (2): 129–149. Bibcode:2016Gbio...14..129B. doi:10.1111/gbi.12165. ISSN1472-4669. PMID26507690.
↑ Riding Robert; Andrey Yu. Zhuravlev (1995). "Structure and 5 thousand years diversity of oldest sponge-microbe reefs: Lower Cambrian, Aldan River, Siberia". Geology. 23 (7): 649–52. doi:10.1130/0091-7613(1995)023<0649:SADOOS>2.3.CO;2.
↑ Finks, R.M. (1970). "The evolution and ecologic history of sponges during Palaeozoic times". In Fry, W.G. (ed.). Biology of the porifera. Symposium of the Zoological Society of London. Vol.25. Academic Press. pp.3–22. ISBN0-12-613325-5. OCLC1409104310.
↑ Hartman, W.D.; Goreau, T.F. (1970). "Jamaican coralline sponges: Their morphology, ecology and fossil relatives". In Fry, W.G. (ed.). Biology of the porifera. Symposium of the Zoological Society of London. Vol.25. Academic Press. pp.205–243. ISBN0-12-613325-5. OCLC1409104310. (Cited by "Notes of the Sclerosponge Workshop". Stable Isotope Laboratory, Rosenstiel School of Marine and Atmospheric Science. Miami, FL: University of Miami. 21–23 March 1998. Archived from the original on 18 August 2018. Retrieved 19 December 2018.)
↑ Vacelet, J. (1985). "Coralline sponges and the evolution of the Porifera". The origins and relationships of lower invertebrates: Proceedings of an International symposium held in London, September 1983. Systematics Association. Vol.28. Clarendon Press. pp.1–13. ISBN0-19-857181-X. OCLC220503346.
Borchiellini, C.; Chombard, C.; Manuel, M.; Alivon, E.; Vacelet, J.; Boury-Esnault, N. (September 2004). "Molecular phylogeny of Demospongiae: implications for classification and scenarios of character evolution". Mol. Phylogenet. Evol. 32 (3): 823–37. Bibcode:2004MolPE..32..823B. doi:10.1016/j.ympev.2004.02.021. PMID15288059.
Kelly-Borges M.; Pomponi S. A. (1994). "Phylogeny and classification of lithistid sponges (Porifera: Demospongiae): a preliminary assessment using ribosomal DNA sequence comparisons". Molecular Marine Biology and Biotechnology. 3 (2): 87–103. PMID8087187.
Reitner, J.; Mehl, D. (1996). Monophyly of the Porifera. Verhandlungen des Naturwissenschaftlichen Vereins in Hamburg. Vol.36. pp.5–32. OCLC833177093.
Sponges or sea sponges are members of the metazoan phylum Porifera, a basal animal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and are one of the most ancient members of macrobenthos, with many historical species being important reef-building organisms.
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.
Polymastia is a genus of sea sponges containing about 30 species. These are small to large encrusting or dome-shaped sponges with a smooth surface having many teat-shaped projections (papillae). In areas of strong wave action, this genus does not grow the teat structures, but instead grows in a corrugated form.
Chondrocladia is a genus of carnivorous demosponges of the family Cladorhizidae. Neocladia was long considered a junior synonym, but recently become accepted as a distinct genus.
Halichondriidae is a family of sea sponges belonging to the order Suberitida. These sponges have a skeleton consisting of dense bundles of spicules occurring in a more or less random pattern.
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.
Plakinidae is a family of marine sponges. It is composed of seven genera:
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.
Bubarida is an order of demosponges in the subclass Heteroscleromorpha.
Clionaida is an order of demosponges in the subclass Heteroscleromorpha.
Scopalinidae is a family of demosponges in the subclass Heteroscleromorpha. It is the only family in the monotypic order Scopalinida.
Tethyida is an order of sea sponges in the subclass Heteroscleromorpha.
Biemnida is an order of demosponges in the subclass Heteroscleromorpha.
Merliida is an order of demosponges in the subclass Heteroscleromorpha, first described as such by Jean Vacelet in 1979.
Trachycladidae is a family of sea sponges in the subclass Heteroscleromorpha. It is the only family in the monotypic order Trachycladida.
Heteroscleromorpha is a subclass of demosponges within the phylum Porifera.
Spongillida is an order of freshwater sponges in the subclass Heteroscleromorpha.
Jean Vacelet is a French marine biologist who specialises in the underwater fauna of the Mediterranean. After earning his licence at the Faculté des Sciences de Marseille and learning to dive in 1954, he specialised in the study of sponges at the Marine station of Endoume, and there he has stayed faithful to both sponges and place for more than half a century. His research has included all aspects of sponges: taxonomy, habitat, biology, anatomy, their bacterial associations, and their place in the evolution of multi-celled animals. He has studied them not only in the Mediterranean but in the Indian Ocean and the Pacific. Exploration of underwater grottoes, together with Jacques Laborel and Jo Hamelin, revealed the existence of sponges dating from very ancient geological periods and the unexpected existence of carnivorous sponges, and surprisingly, the grottoes in some ways mimicked life at much greater depths.
Coelosphaeridae is a family of sponges belonging to the order Poecilosclerida. Species are found across the globe.
Abyssocladia is a genus of the family Cladorhizidae, a family of carnivorous sponges. It is made up of at least 39 species found in oceans all over the world.
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