Editing Sponge (section)

== Distinguishing features ==

{{Further|Cnidaria|Ctenophore}}

Sponges constitute the [[phylum]] Porifera, and have been defined as [[Sessility (motility)|sessile]] [[metazoa]]ns (multicelled immobile animals) that have water intake and outlet openings connected by chambers lined with [[choanocyte]]s, cells with whip-like flagella.<ref name="Bergquist_1978"/>{{rp|29}} However, a few carnivorous sponges have lost these water flow systems and the choanocytes.<ref name="Bergquist_1978"/>{{rp|39}}<ref name="Hooper_2002">{{cite book |author1=Hooper, J. N. A. |author2=Van Soest, R. W. M. |author3=Debrenne, F. |contribution=Phylum Porifera Grant, 1836|pages=9–14 |editor1=Hooper, J. N. A. |editor2=Van Soest, R. W. M. |title=Systema Porifera: A Guide to the Classification of Sponges |publisher=Kluwer Academic/Plenum |location=New York |url={{google books |plainurl=y |id=OQoxzqjQXWEC|page=220}}|year=2002 |isbn=978-0-306-47260-2}}</ref> All known living sponges can remold their bodies, as most types of their cells can move within their bodies and a few can change from one type to another.<ref name="Hooper_2002"/><ref name="Ruppert_2004">{{cite book |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard S. |last3=Barnes |first3=Robert D. |title=Invertebrate Zoology |publisher=Brooks / [[COLE Publishing]] |edition=7th |isbn=978-0-03-025982-1 |year=2004 |url-access=registration |url=https://archive.org/details/isbn_9780030259821 |pages=76–97}}</ref>

Even if a few sponges are able to produce mucus – which acts as a microbial barrier in all other animals – no sponge with the ability to secrete a functional mucus layer has been recorded. Without such a mucus layer their living tissue is covered by a layer of microbial symbionts, which can contribute up to 40–50% of the sponge wet mass. This inability to prevent microbes from penetrating their porous tissue could be a major reason why they have never evolved a more complex anatomy.<ref>{{cite journal |last1=Bakshani |first1=Cassie R. |last2=Morales-Garcia |first2=Ana L. |last3=Althaus |first3=Mike |last4=Wilcox |first4=Matthew D. |last5=Pearson |first5=Jeffrey P. |last6=Bythell |first6=John C. |last7=Burgess |first7=J. Grant |title=Evolutionary conservation of the antimicrobial function of mucus: a first defence against infection |journal=npj Biofilms and Microbiomes |volume=4 |issue=1 |page=14 |date=2018-07-04 |pmid=30002868 |pmc=6031612 |doi=10.1038/s41522-018-0057-2 }}</ref>

Like [[cnidaria]]ns (jellyfish, etc.) and [[Ctenophora|ctenophores]] (comb jellies), and unlike all other known metazoans, sponges' bodies consist of a non-living jelly-like mass ([[mesohyl]]) sandwiched between two main layers of cells.<ref name="Bergquist_1998"/><ref name="Hinde_2001">{{cite book |last=Hinde |first=R. T. |year=1998 |chapter=The Cnidaria and Ctenophora|pages=28–57 |editor-last=Anderson |editor-first=D. T. |title=Invertebrate Zoology |publisher=[[Oxford University Press]] |isbn=978-0-19-551368-4}}</ref> Cnidarians and ctenophores have simple nervous systems, and their cell layers are bound by internal connections and by being mounted on a basement membrane (thin fibrous mat, also known as "[[basal lamina]]").<ref name="Hinde_2001"/> Sponges do not have a nervous system similar to that of vertebrates but may have one that is quite different.<ref name="Moroz_2022"/> Their middle jelly-like layers have large and varied populations of cells, and some types of cells in their outer layers may move into the middle layer and change their functions.<ref name="Ruppert_2004"/>

{|class="wikitable" <!-- width="45%" --> style="margin-left:4px"
|-
!  !! Sponges<ref name="Ruppert_2004"/><ref name="Bergquist_1998"/> !! [[Cnidarian]]s and [[ctenophore]]s<ref name="Hinde_2001"/>
|-
! Nervous system
|No/Yes ||Yes, simple
|-
! Cells in each layer bound together
|No, except that [[Homoscleromorpha]] have basement membranes.<ref name="Exposito_2002"/> ||Yes: inter-cell connections; basement membranes
|-
! Number of cells in middle "jelly" layer
|Many ||Few
|-
! Cells in outer layers can move inwards and change functions
|Yes ||No
|}