Editing Sponge (section)

== Overview ==
[[File:Reef3859 - Flickr - NOAA Photo Library.jpg|thumb|right|Sponge [[biodiversity]] and [[morphotype]]s at the lip of a wall site in {{convert|60|ft|m|-1}} of water. Included are the yellow tube sponge, ''[[Aplysina fistularis]]'', the purple vase sponge, ''[[Niphates digitalis]]'', the red encrusting sponge, ''[[Spirastrella coccinea]]'', and the gray rope sponge, ''[[Callyspongia]]'' sp.]]

Sponges are similar to other animals in that they are [[Multicellular organism|multicellular]], [[heterotroph]]ic, lack [[cell wall]]s and produce [[sperm cell]]s. Unlike other animals, they lack true [[Tissue (biology)|tissues]]<ref name="Hooper">{{cite web |url= https://www.qm.qld.gov.au/microsites/biodiscovery/03sponges-and-corals/structure-of-sponges.html |title=Structure of Sponges |last= Hooper |first=J. |year=2018 |website=Queensland Museum |access-date=27 September 2019 |archive-url=https://web.archive.org/web/20190926205031/https://www.qm.qld.gov.au/microsites/biodiscovery/03sponges-and-corals/structure-of-sponges.html |archive-date=26 September 2019 |url-status=dead }}</ref> and [[Organ (anatomy)|organs]].<ref>{{cite journal |last1=Thacker |first1=Robert W. |last2=Díaz |first2=Maria Cristina |last3=Kerner |first3=Adeline |last4=Vignes-Lebbe |first4=Régine |last5=Segerdell |first5=Erik |last6=Haendel |first6=Melissa A. |last7=Mungall |first7=Christopher J. |title=The Porifera Ontology (PORO): enhancing sponge systematics with an anatomy ontology |journal=Journal of Biomedical Semantics |volume=5 |issue=1 |pages=39 |date=8 September 2014 |pmid=25276334 |pmc=4177528 |doi=10.1186/2041-1480-5-39 |doi-access=free }}</ref> Some of them are radially symmetrical, but most are asymmetrical. The shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where the water deposits nutrients and then leaves through a hole called the [[osculum]]. The [[unicellular|single-celled]] [[choanoflagellate]]s resemble the [[choanocyte]] cells of sponges which are used to drive their water flow systems and capture most of their food. This along with phylogenetic studies of ribosomal molecules have been used as morphological evidence to suggest sponges are the sister group to the rest of animals.<ref name="Collins_1998">{{cite journal |last=Collins |first=A.G. |title=Evaluating multiple alternative hypotheses for the origin of Bilateria: an analysis of 18S rRNA molecular evidence |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=95 |issue=26 |pages=15458–63 |date=December 1998 |pmid=9860990 |pmc=28064 |doi=10.1073/pnas.95.26.15458 |bibcode=1998PNAS...9515458C |doi-access=free }}</ref> A great majority are marine (salt-water) species, ranging in habitat from tidal zones to depths exceeding {{convert|8,800|m|mi|abbr=on}}, though there are freshwater species. All adult sponges are [[Sessility (motility)|sessile]], meaning that they attach to an underwater surface and remain fixed in place (i.e., do not travel). While in their [[larvae|larval stage]] of life, they are [[motility|motile]].

Many sponges have internal skeletons of spicules (skeletal-like fragments of [[calcium carbonate]] or [[silicon dioxide]]), and/or [[spongin]] (a modified type of collagen protein).<ref name="Hooper"/> An internal gelatinous [[matrix (biology)|matrix]] called mesohyl functions as an [[endoskeleton]], and it is the only skeleton in soft sponges that encrust such hard surfaces as rocks. More commonly, the mesohyl is stiffened by [[Biomineralization|mineral]] [[sponge spicule|spicules]], by spongin fibers, or both. Most sponges (over 90% of all known species) are [[demosponge]]s, which have the widest range of habitats (including all freshwater ones); they use spongin, [[silica]] spicules, or both, and some species have calcium carbonate [[exoskeleton]]s. [[Calcareous sponge|Calcarean]]s have calcium carbonate spicules and, in some species, calcium carbonate exoskeletons; they are restricted to relatively shallow marine waters where production of calcium carbonate is easiest.<ref name="Bergquist_1978"/>{{rp|179}} The fragile [[glass sponge|hexactinellids or glass sponge]]s use "[[scaffolding]]" of silica spicules and are restricted to polar regions or ocean depths where predators are rare. Fossils of all of these types have been found in rocks dated from {{ma|580}}. In addition [[Archaeocyathid]]s, whose fossils are common in rocks from {{ma|530|490}}, are now regarded as a type of sponge. The smallest class of extant sponges are [[Homosclerophorida|homoscleromorphs]], which either have calcium carbonate spicules like the calcereans or are aspiculate, and found in shaded marine environments like caves and overhangs.

Although most of the approximately 5,000–10,000&nbsp;known species of sponges feed on [[bacteria]] and other microscopic food in the water, some host [[photosynthesis|photosynthesizing]] microorganisms as [[endosymbiont]]s, and these alliances often produce more food and oxygen than they consume. A few species of sponges that live in food-poor environments have evolved as [[carnivore]]s that prey mainly on small [[crustacean]]s.<ref>{{cite journal |last1=Vacelet |first1=J. |last2=Duport |first2=E. |title=Prey capture and digestion in the carnivorous sponge ''Asbestopluma hypogea'' (Porifera: Demospongiae)|year=2004|journal=[[Zoomorphology]]|volume=123|issue=4|pages=179–190|s2cid=24484610 |doi=10.1007/s00435-004-0100-0 }}</ref>

Most sponges reproduce [[sexual reproduction|sexually]], but they can also reproduce asexually. Sexually reproducing species release [[sperm]] cells into the water to fertilize [[ovum|ova]] released or retained by its mate or "mother"; the fertilized eggs develop into [[larva]]e which swim off in search of places to settle.<ref name="Bergquist_1978">{{Cite book |last=Bergquist |first=P. R. |year=1978 |title=Sponges |publisher=Hutchinson |location=London |isbn=978-0-520-03658-1}}</ref>{{rp|183–185}} Sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. Some species reproduce by budding. When environmental conditions become less hospitable to the sponges, for example as temperatures drop, many freshwater species and a few marine ones produce [[gemmule]]s, "survival pods" of unspecialized cells that remain dormant until conditions improve; they then either form completely new sponges or recolonize the skeletons of their parents.<ref name="Bergquist_1978"/>{{rp|120–127}}

[[File:Choanoflagellate and choanocyte.png|thumb|upright=1.8|Cells of the protist choanoflagellate clade closely resemble sponge choanocyte cells. Beating of choanocyte [[flagella]] draws water through the sponge so that nutrients can be extracted and waste removed.<ref>Clark, M.A.; Choi, J.; Douglas, M. (2018) [https://web.archive.org/web/20191011015411/https://d3bxy9euw4e147.cloudfront.net/oscms-prodcms/media/documents/Biology2e-OP.pdf ''Biology 2e''], page 776, ''OpenStax''. {{ISBN|978-1-947172-52-4}}.</ref>]]

The few species of demosponge that have entirely soft fibrous skeletons with no hard elements have been used by humans over thousands of years for several purposes, including as padding and as cleaning tools. By the 1950s, though, these had been [[overfishing|overfished]] so heavily that the industry almost collapsed, and most sponge-like materials are now synthetic. Sponges and their microscopic endosymbionts are now being researched as possible sources of medicines for treating a wide range of diseases. [[Dolphin]]s have been observed using sponges as tools while [[foraging]].<ref name="Krutzen_2005"/>