Editing Sponge (section)

== Basic structure ==
<!--[[File:Tide pools sponge.jpg|A pink sponge in a [[tide pool]]|thumb]]
[[File:Aphrocallistes vastus.jpg|thumb|''Aphrocallistes vastus'' (cloud sponge) is a type of glass sponge. They are very fragile, as they are made out of tiny glass crystals ([[hydrated silica]] dioxide).<ref>{{cite web|url=http://www.biology.ualberta.ca/faculty/sally_leys/uploads/personal/Glass%20sponge%20ecology.htm|title=Studies in Life Sciences, University of Alberta: Glass Sponge Ecology|work=Department of Biological Sciences|access-date=2008-03-16|archive-url=https://web.archive.org/web/20120715083546/http://www.biology.ualberta.ca/faculty/sally_leys/uploads/personal/Glass%20sponge%20ecology.htm|archive-date=July 15, 2012|url-status=live}}</ref>]]-->

=== Cell types ===

{{anchor|Ostium (sponges)}}
{{Annotated image/Porifera cell types}}
A sponge's body is hollow and is held in shape by the [[mesohyl]], a jelly-like substance made mainly of [[collagen]] and reinforced by a dense network of fibers also made of collagen. 18 distinct cell types have been identified.<ref>{{cite journal |last1=Musser |first1=Jacob M. |last2=Schippers |first2=Klaske J. |last3=Nickel |first3=Michael |last4=Mizzon |first4=Giulia |last5=Kohn |first5=Andrea B. |last6=Pape |first6=Constantin |last7=Ronchi |first7=Paolo |last8=Papadopoulos |first8=Nikolaos |last9=Tarashansky |first9=Alexander J. |last10=Hammel |first10=Jörg U. |last11=Wolf |first11=Florian |last12=Liang |first12=Cong |last13=Hernández-Plaza |first13=Ana |last14=Cantalapiedra |first14=Carlos P. |last15=Achim |first15=Kaia |last16=Schieber |first16=Nicole L. |last17=Pan |first17=Leslie |last18=Ruperti |first18=Fabian |last19=Francis |first19=Warren R. |last20=Vargas |first20=Sergio |last21=Kling |first21=Svenja |last22=Renkert |first22=Maike |last23=Polikarpov |first23=Maxim |last24=Bourenkov |first24=Gleb |last25=Feuda |first25=Roberto |last26=Gaspar |first26=Imre |last27=Burkhardt |first27=Pawel |last28=Wang |first28=Bo |last29=Bork |first29=Peer |last30=Beck |first30=Martin |last31=Schneider |first31=Thomas R. |last32=Kreshuk |first32=Anna |last33=Wörheide |first33=Gert |last34=Huerta-Cepas |first34=Jaime |last35=Schwab |first35=Yannick |last36=Moroz |first36=Leonid L. |last37=Arendt |first37=Detlev |display-authors=6 |title=Profiling cellular diversity in sponges informs animal cell type and nervous system evolution |journal=Science |volume=374 |issue=6568 |pages=717–723 |date=November 2021 |pmid=34735222 |pmc=9233960 |doi=10.1126/science.abj2949 |bibcode=2021Sci...374..717M }}</ref> The inner surface is covered with [[choanocyte]]s, cells with cylindrical or conical collars surrounding one [[flagellum]] per choanocyte. The wave-like motion of the whip-like flagella drives water through the sponge's body. All sponges have '''ostia''', channels leading to the interior through the mesohyl, and in most sponges these are controlled by tube-like [[porocytes]] that form closable inlet valves. [[Pinacocyte]]s, plate-like cells, form a single-layered external skin over all other parts of the mesohyl that are not covered by choanocytes, and the pinacocytes also digest food particles that are too large to enter the ostia,<ref name="Ruppert_2004"/><ref name="Bergquist_1998"/> while those at the base of the animal are responsible for anchoring it.<ref name="Bergquist_1998"/>

Other types of cells live and move within the mesohyl:<ref name="Ruppert_2004"/><ref name="Bergquist_1998"/>
* [[Lophocyte]]s are [[amoeba]]-like cells that move slowly through the mesohyl and secrete collagen fibres.
* [[Collencyte]]s are another type of collagen-producing cell.
* [[Rhabdiferous]] cells secrete [[polysaccharide]]s that also form part of the mesohyl.
* [[Oocyte]]s and [[spermatocyte]]s are reproductive cells.
* [[Sclerocyte]]s secrete the mineralized [[sponge spicule|spicules]] ("little spines") that form the [[skeleton]]s of many sponges and in some species provide some defense against predators.
* In addition to or instead of sclerocytes, [[demosponge]]s have [[spongocyte]]s that secrete a form of collagen that [[polymer]]izes into [[spongin]], a thick fibrous material that stiffens the mesohyl.
* [[Myocyte]]s ("muscle cells") conduct signals and cause parts of the animal to contract.
* "Grey cells" act as sponges' equivalent of an [[immune system]].
* [[Archaeocytes]] (or [[amoebocytes]]) are [[amoeba]]-like cells that are [[totipotent]], in other words, each is capable of transformation into any other type of cell. They also have important roles in feeding and in clearing debris that block the ostia.

Many larval sponges possess neuron-less [[eye]]s that are based on [[cryptochrome]]s. They mediate phototaxic behavior.<ref>{{cite journal |last1=Rivera |first1=A.S. |last2=Ozturk |first2=N. |last3=Fahey |first3=B. |last4=Plachetzki |first4=D.C. |last5=Degnan |first5=B.M. |last6=Sancar |first6=A. |last7=Oakley |first7=T.H. |title=Blue-light-receptive cryptochrome is expressed in a sponge eye lacking neurons and opsin |journal=The Journal of Experimental Biology |volume=215 |issue=Pt 8 |pages=1278–86 |date=April 2012 |pmid=22442365 |pmc=3309880 |doi=10.1242/jeb.067140 |bibcode=2012JExpB.215.1278R }}</ref>

[[Glass sponge]]s present a distinctive variation on this basic plan. Their spicules, which are made of [[silica]], form a [[scaffolding]]-like framework between whose rods the living tissue is suspended like a [[Spider web|cobweb]] that contains most of the cell types.<ref name="Ruppert_2004"/> This tissue is a [[Hexactinellid#Syncytia|syncytium]] that in some ways behaves like many cells that share a single external [[Cell membrane|membrane]], and in others like a single cell with multiple [[cell nucleus|nuclei]].

=== Water flow and body structures ===

{{Annotated image |float={{{float|right}}} |caption=[[Porifera]] body structures<ref>{{cite book
|last1=Ruppert|first1=Edward E.|last2=Fox|first2=Richard S.|last3=Barnes|first3=Robert D. |title=Invertebrate Zoology |publisher=Brooks / Cole |edition=7th |isbn=978-0-03-025982-1 |date=2004 |page=78 |ref=none}}</ref> |image=Porifera body structures 01.png |width=280 |image-width=280 |height=205
|annotations=
{{Annotation|5|150|'''Asconoid'''}}
{{Annotation|105|150|'''Syconoid'''}}
{{Annotation|205|150|'''Leuconoid'''}}
{{Annotation|5|170|<span style{{=}}"background-color:yellow; border: solix 1px silver">&nbsp;&nbsp;&nbsp;</span> [[Pinacocyte]]s}}
{{Annotation|5|190|<span style{{=}}"background-color:red; border:solix 1px silver">&nbsp;&nbsp;&nbsp;</span> [[Choanocyte]]s}}
{{Annotation|145|170|<span style{{=}}"background-color:#c0c0c0; border:solix 1px silver">&nbsp;&nbsp;&nbsp;</span> [[Mesohyl]]}}
{{Annotation|145|190|<span style{{=}}"background-color:#00ffff; border: solix 1px silver">&nbsp;&nbsp;&nbsp;</span> Water flow}}
}}

Most sponges work rather like [[chimney]]s: they take in water at the bottom and eject it from the [[osculum]] at the top. Since ambient currents are faster at the top, the suction effect that they produce by [[Bernoulli's principle]] does some of the work for free. Sponges can control the water flow by various combinations of wholly or partially closing the osculum and ostia (the intake pores) and varying the beat of the flagella, and may shut it down if there is a lot of sand or silt in the water.<ref name="Ruppert_2004"/>

Although the layers of [[pinacocyte]]s and [[choanocyte]]s resemble the [[epithelia]] of more complex animals, they are not bound tightly by cell-to-cell connections or a basal lamina (thin fibrous sheet underneath). The flexibility of these layers and re-modeling of the mesohyl by lophocytes allow the animals to adjust their shapes throughout their lives to take maximum advantage of local water currents.<ref name="Ruppert_2004"/>{{rp|83}}

The simplest body structure in sponges is a tube or vase shape known as "asconoid", but this severely limits the size of the animal. The body structure is characterized by a stalk-like spongocoel surrounded by a single layer of choanocytes. If it is simply scaled up, the ratio of its volume to surface area increases, because surface increases as the square of length or width while volume increases proportionally to the cube. The amount of tissue that needs food and [[oxygen]] is determined by the volume, but the pumping capacity that supplies food and oxygen depends on the area covered by choanocytes. Asconoid sponges seldom exceed {{convert|1|mm|in|abbr=on}} in diameter.<ref name="Ruppert_2004"/>

[[File:Sea sponge diagram.svg|thumb|250px|left|Diagram of a syconoid sponge]]

Some sponges overcome this limitation by adopting the "syconoid" structure, in which the body wall is [[pleat]]ed. The inner pockets of the pleats are lined with choanocytes, which connect to the outer pockets of the pleats by ostia. This increase in the number of choanocytes and hence in pumping capacity enables syconoid sponges to grow up to a few centimeters in diameter.

{{anchor|leuconoid}}The "leuconoid" pattern boosts pumping capacity further by filling the interior almost completely with mesohyl that contains a network of chambers lined with choanocytes and connected to each other and to the water intakes and outlet by tubes. Leuconid sponges grow to over {{convert|1|m|ft|abbr=on}} in diameter, and the fact that growth in any direction increases the number of choanocyte chambers enables them to take a wider range of forms, for example, "encrusting" sponges whose shapes follow those of the surfaces to which they attach. All freshwater and most shallow-water marine sponges have leuconid bodies. The networks of water passages in [[glass sponge]]s are similar to the leuconid structure.<ref name="Ruppert_2004"/>

In all three types of structure, the cross-section area of the choanocyte-lined regions is much greater than that of the intake and outlet channels. This makes the flow slower near the choanocytes and thus makes it easier for them to trap food particles.<ref name="Ruppert_2004"/> For example, in ''[[Leuconia]]'', a small leuconoid sponge about {{convert|10|cm|in}} tall and {{convert|1|cm|in}} in diameter, water enters each of more than 80,000 intake canals at 6&nbsp;cm per ''minute''. However, because ''Leuconia'' has more than 2&nbsp;million flagellated chambers whose combined diameter is much greater than that of the canals, water flow through chambers slows to 3.6&nbsp;cm per ''hour'', making it easy for choanocytes to capture food. All the water is expelled through a single [[osculum]] at about 8.5&nbsp;cm per ''second'', fast enough to carry waste products some distance away.<ref>{{cite book |author1=Hickman, C.P. |author2=Roberts, L.S. |author3=Larson, A. |year=2001 |title=Integrated Principles of Zoology |edition=11th |publisher=[[McGraw-Hill]] |location=New York |isbn=978-0-07-290961-6 |page=247}}</ref>

[[File:Porifera calcifying 01.png|thumb|Sponge with calcium carbonate skeleton.<ref name="Ruppert_2004"/>
{{legend-col
|{{legend|yellow|[[Pinacocyte]]}}
|{{legend|red|[[Choanocyte]]}}
|{{legend|lime|[[Archeocyte]]s and other cells in [[mesohyl]]}}
|{{legend|#d6d6d6|Mesohyl}}
|{{legend|#5d5d5d|Spicules}}
|{{legend|#ff8000|[[Calcium carbonate]]}}
|{{legend|#804000|Seabed / rock}}
|{{legend|#00ffff|Water flow}}
}}
]]

=== Skeleton ===

In zoology, a [[skeleton]] is any fairly rigid structure of an animal, irrespective of whether it has joints and irrespective of whether it is [[biomineralization|biomineralized]]. The mesohyl functions as an [[endoskeleton]] in most sponges, and is the only skeleton in soft sponges that encrust hard surfaces such as rocks. More commonly the mesohyl is stiffened by mineral [[sponge spicule|spicules]], by spongin fibers or both. Spicules, which are present in most but not all species,<ref>{{Cite web |url=http://species-identification.org/species.php?species_group=sponges&id=259 |title=Marine Species Identification Portal: Halisarca dujardini|website=species-identification.org |access-date=2019-08-02 |archive-date=2020-10-17 |archive-url=https://web.archive.org/web/20201017130847/http://species-identification.org/species.php?species_group=sponges&id=259 |url-status=dead}}</ref> may be made of [[silica]] or calcium carbonate, and vary in shape from simple rods to three-dimensional "stars" with up to six rays. Spicules are produced by [[sclerocyte]] cells,<ref name="Ruppert_2004"/> and may be separate, connected by joints, or fused.<ref name="Hooper_2002"/>

Some sponges also secrete [[exoskeleton]]s that lie completely outside their organic components. For example, [[sclerosponge]]s ("hard sponges") have massive calcium carbonate exoskeletons over which the organic matter forms a thin layer with [[choanocyte]] chambers in pits in the mineral. These exoskeletons are secreted by the [[pinacocyte]]s that form the animals' skins.<ref name="Ruppert_2004"/>