Editing Sponge (section)

=== 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}}
}}
]]