View source for Hexactinellid

{{short description|Class of sponges with siliceous spicules}}
{{Automatic taxobox
| name = Glass sponges
| fossil_range = Late [[Ediacaran]]–present{{fossil range|544|0|<ref name="Brasier1997">{{cite journal | last1 = Brasier | first1 = Martin | last2 = Green | first2 = Owen | last3 = Shields | first3 = Graham | date = April 1997 | title = Ediacarian sponge spicule clusters from southwestern Mongolia and the origins of the Cambrian fauna |url=https://www.researchgate.net/publication/240669632 |format=PDF | journal = Geology | volume = 25 | issue = 4 | pages = 303–306 | doi = 10.1130/0091-7613(1997)025<0303:ESSCFS>2.3.CO;2 | bibcode = 1997Geo....25..303B }}</ref>}}
| image = Haeckel Hexactinellae.jpg
| image_caption = "Hexactinellae" from [[Ernst Haeckel]]'s ''[[Kunstformen der Natur]]'', 1904
| taxon = Hexactinellida
| authority = Schmidt, 1870
| subdivision_ranks = Subgroups
| subdivision = [[#Classification|See text]].
| synonyms = * Hyalospongiae
}}
[[File:Bolosoma stalked glass sponge (39506105791).jpg|thumb|Bolosoma stalked glass sponge]]
'''Hexactinellid sponges''' are [[sponge]]s with a [[skeleton]] made of four- and/or six-pointed [[silica|siliceous]] [[spicule (sponge)|spicule]]s, often referred to as '''glass sponges'''. They are usually [[biological classification|classified]] along with other sponges in the [[phylum]] [[Porifera]], but some researchers consider them sufficiently distinct to deserve their own phylum, '''Symplasma'''. Some experts believe that glass sponges are the longest-lived animals on earth;<ref>{{Cite web |title=Hexactinellid sponge (Scolymastra joubini) longevity, ageing, and life history |url=https://genomics.senescence.info/species/entry.php?species=Scolymastra_joubini |access-date=2 March 2023 |website=genomics.senescence.info}}</ref> these scientists tentatively estimate a maximum age of up to 15,000 years.

== Biology ==
Glass sponges are relatively uncommon and are mostly found at depths from {{convert|450|to|900|m|ft}} below sea level. Although the species ''[[Oopsacas minuta]]'' has been found in shallow water, others have been found much deeper. They are found in all oceans of the world, although they are particularly common in [[Antarctic]] and Northern Pacific waters.<ref name=IZ>{{cite book |author= Barnes, Robert D. |year=1982 |title= Invertebrate Zoology |publisher= Holt-Saunders International |location=Philadelphia |page= 104 |isbn= 978-0-03-056747-6}}</ref>

They are more-or-less cup-shaped animals, ranging from {{convert|10|to|30|cm|in}} in height, with sturdy skeletons made of [[glass]]-like [[silica]] [[Sponge spicule|spicules]], fused to form a lattice.<ref>{{Cite web |date=2020-10-01 |title=Glass Sponges, the Living Ornaments of the Deep Sea |url=https://schmidtocean.org/cruise-log-post/glass-sponges-the-living-ornaments-of-the-deep-sea/ |access-date=2023-06-11 |website=Schmidt Ocean Institute |language=en-US}}</ref><ref>{{Cite web |last=US Department of Commerce |first=National Oceanic and Atmospheric Administration |title=What is a glass sponge? |url=https://oceanservice.noaa.gov/facts/glass-sponge.html |access-date=2023-06-11 |website=oceanservice.noaa.gov |language=EN-US}}</ref> In some glass sponges such as members of the genus ''Euplectela'', these structures are aided by a protein called glassin. It helps accelerate the production of silicas from the silicic acid absorbed from the surrounding seawater.<ref name="Nishi 739–747">{{Cite journal |last1=Nishi |first1=Michika |last2=Kobayashi |first2=Hiroki |last3=Amano |first3=Taro |last4=Sakate |first4=Yuto |last5=Bito |first5=Tomohiro |last6=Arima |first6=Jiro |last7=Shimizu |first7=Katsuhiko |date=2020-12-01 |title=Identification of the Domains Involved in Promotion of Silica Formation in Glassin, a Protein Occluded in Hexactinellid Sponge Biosilica, for Development of a Tag for Purification and Immobilization of Recombinant Proteins |url=https://doi.org/10.1007/s10126-020-09967-2 |journal=Marine Biotechnology |language=en |volume=22 |issue=6 |pages=739–747 |doi=10.1007/s10126-020-09967-2 |pmid=32291549 |bibcode=2020MarBt..22..739N |s2cid=215761084 |issn=1436-2236|url-access=subscription }}</ref> The body is relatively symmetrical, with a large central cavity that, in many species, opens to the outside through a sieve formed from the skeleton. Some species of glass sponges are capable of fusing together to create reefs or [[bioherm]]s. They are generally pale in colour, ranging from white to orange.<ref name=IZ/>

Much of the body is composed of [[Syncytium|syncitial tissue]], extensive regions of [[multinucleate]] [[cytoplasm]]. The epidermal cells characteristic of other sponges are absent, being replaced by a syncitial net of [[amoebocyte]]s, through which the spicules penetrate. Unlike other sponges, they do not possess the ability to contract.<ref name=IZ/>

Their bodies comprises three parts: the inner and outer peripheral trabecular networks and the [[choanosome]], which is used for feeding purposes. The choanosome acts as the mouth for the sponge while the inner and outer canals that meet at the choanosome are passages for the food, creating a consumption path for the sponge.<ref>{{Cite web|url=https://link.gale.com/apps/doc/CX3406700021/GVRL|title=Gale - Institution Finder}}</ref>

All hexactinellids have the potential to grow to different sizes, but the average maximum growth is estimated to be around 32 centimeters long. Some grow past that length and continue to extend their lengths up to 1 meter. The estimated life expectancy for hexactinellids that grow around 1 meter is approximately 200 years (Plyes).

[[File:Euplectella 01.png|thumb|left|The [[glass sponge]] ''[[Euplectella]]''.<ref name = "Ruppert_2004">{{cite book | vauthors = Ruppert RE, Fox RS, Barnes RD |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>{{rp|83 Fig. 5–7}}
{{legend|#4848ff|Water flow}}
{{legend|#c0c0c0|Main [[syncitium]]}}
{{legend|#6a6a6a|[[Sponge spicule|Spicules]]}}
{{legend|red|[[Choanosyncitium]] and collar bodies showing interior}}
]]

Glass sponges possess a unique system for rapidly conducting electrical impulses across their bodies, making it possible for them to respond quickly to external stimuli.<ref>{{cite journal| url = http://www.nature.com/news/1999/990415/full/news990415-5.html| title = Nervous sponge| date = 1999| doi = 10.1038/news990415-5| last1 = Lawrence| first1 = Eleanor| journal = Nature| url-access = subscription}}</ref> In the case ''Rhabdocalyptus dawsoni,'' the sponge uses electrical neuron signaling to detect outside stimuli, such as sediments, and then send a signal through its body system to alert the organism to no longer be actively feeding. Another glass sponge species in the same experiment of ''R. dawsoni'' showed that the electrical conduction system for this class of sponges has its own threshold of how much outside stimuli, sediments, etc., it can endure before it will stop its feeding process'''.'''<ref>{{Cite journal |last1=Tompkins-MacDonald |first1=Gabrielle J. |last2=Leys |first2=Sally P. |date=2008-05-15 |title=Glass sponges arrest pumping in response to sediment: implications for the physiology of the hexactinellid conduction system |url=http://dx.doi.org/10.1007/s00227-008-0987-y |journal=Marine Biology |volume=154 |issue=6 |pages=973–984 |doi=10.1007/s00227-008-0987-y |bibcode=2008MarBi.154..973T |s2cid=54079172 |issn=0025-3162|url-access=subscription }}</ref> Species like [[Venus' flower basket]] have a tuft of fibers that extends outward like an inverted crown at the bases of their skeletons. These fibers are {{convert|50|to|175|mm|in}} long and about the thickness of a human hair.

=== Syncytia ===
Bodies of glass sponges are different from those of other sponges in various other ways. For example, most of their cytoplasm is not divided into separate cells by membranes, but forms a [[syncytium]] or continuous mass of cytoplasm with many [[cell nucleus|nuclei]] (e.g., Reiswig and Mackie, 1983); it is held suspended like a [[spider web|cobweb]] by a [[scaffolding]]-like framework made of [[silica]] spicules.<ref name="Ruppert_2004" /> The remaining cells are connected to the syncytium by bridges of [[cytoplasm]]ic "rivers" that transport nuclei, [[organelle]]s, and other substances.<ref name="Leys_2003">{{cite journal | vauthors = Leys SP | title = The significance of syncytial tissues for the position of the hexactinellida in the metazoa | journal = Integrative and Comparative Biology | volume = 43 | issue = 1 | pages = 19–27 | date = February 2003 | pmid = 21680406 | doi = 10.1093/icb/43.1.19 | doi-access = free }}</ref> Instead of choanocytes, these bridges have further syncytia, known as choanosyncytia, which form bell-shaped chambers where water enters via perforations. The insides of these chambers are lined with "collar bodies", each consisting of a collar and flagellum but without a nucleus of its own. The motion of the flagella sucks water through passages in the "cobweb" and expels it via the open ends of the bell-shaped chambers.<ref name="Ruppert_2004" />

Some types of cells have a single nucleus and membrane each but are connected to other single-nucleus cells and to the main syncytium by "bridges" made of [[cytoplasm]]. The [[sclerocyte]]s that build spicules have multiple nuclei, and in glass sponge larvae they are connected to other tissues by cytoplasm bridges; such connections between sclerocytes have not so far been found in adults, but this may simply reflect the difficulty of investigating such small-scale features. The bridges are controlled by "plugged junctions" that apparently permit some substances to pass while blocking others.<ref name="Leys_2003" />

This physiology is what allows for a greater flow of ions and electrical signals to move throughout the organism, with around 75% of the sponge tissue being fused in this way.<ref name="Nishi 739–747" /> Another way is their role in the nutrient cycles of deep-sea environments. One species for example, ''Vazella pourtalesii'', has an abundance of symbiotic microbes which aid in the nitrification and denitrification of their communities. These interactions help the sponges survive in the low-oxygen conditions of the depths.<ref>{{Cite journal |last1=Maldonado |first1=Manuel |last2=López-Acosta |first2=María |last3=Busch |first3=Kathrin |last4=Slaby |first4=Beate M. |last5=Bayer |first5=Kristina |last6=Beazley |first6=Lindsay |last7=Hentschel |first7=Ute |last8=Kenchington |first8=Ellen |last9=Rapp |first9=Hans Tore |date=2021 |title=A Microbial Nitrogen Engine Modulated by Bacteriosyncytia in Hexactinellid Sponges: Ecological Implications for Deep-Sea Communities |journal=Frontiers in Marine Science |volume=8 |doi=10.3389/fmars.2021.638505 |issn=2296-7745 |doi-access=free |hdl=10261/235467 |hdl-access=free }}</ref>

=== Longevity ===
[[Image:Venus Flower Basket.jpg|thumb|[[Venus' flower basket]], ''Euplectella aspergillum'']]
[[File:Glass-sponge, Euplectella aspergillum.jpg|thumb|Euplectella aspergillum]]
These creatures are long-lived, but the exact age is hard to measure; one study based on modelling gave an estimated age of a specimen of ''[[Anoxycalyx joubini|Scolymastra joubini]]'' as 23,000 years (with a range from 13,000 to 40,000 years). However, due to changes in sea levels since the [[Last Glacial Maximum]], its maximum age is thought to be no more than 15,000 years,<ref>{{cite journal
 |author=Susanne Gatti 
 |year=2002 
 |title=The Role of Sponges in High-Antarctic Carbon and Silicon Cycling - a Modelling Approach 
 |journal=Ber. Polarforsch. Meeresforsch 
 |volume=434 
 |issn=1618-3193 
 |url=http://epic.awi.de/Publications/BerPolarforsch2002434.pdf 
 |access-date=2009-05-25 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20110724175156/http://epic.awi.de/Publications/BerPolarforsch2002434.pdf 
 |archive-date=2011-07-24 
}}</ref> hence its listing of c. 15,000 years in the AnAge Database.<ref>{{cite web| url = http://genomics.senescence.info/species/entry.php?species=Scolymastra_joubini| title = Hexactinellid information from the AnAge Database}}</ref> The shallow-water occurrence of hexactinellids is rare worldwide. In the [[Antarctic]], two species occur as shallow as 33 meters under the ice. In the [[Mediterranean Sea|Mediterranean]], one species occurs as shallow as {{convert|18|m|ft}} in a cave with deep-water upwelling (Boury-Esnault & Vacelet (1994))

<gallery widths="200px" heights="200px">
File:Staurocalyptus- noaa photo expl0951.jpg|''[[Staurocalyptus]]'' sp.
File:Hexactinellida.jpg|Various hexactinellid sponges.
Image:SpongeXenophorid.jpg|Hexactinellid sponge on a [[Xenophoridae|xenophorid]] gastropod.
Image:Pattersonia ulrichi Rauff, 1894.JPG|''Pattersonia ulrichi'' Rauff, 1894; an Ordovician hexactinellid sponge from near Cincinnati, Ohio.
</gallery>

==Reefs==
The sponges form reefs (called [[sponge reef]]s) off the coast of [[British Columbia]], [[Southeast Alaska]], and [[Washington (state)|Washington state]],<ref>{{cite news | first1=Lisa | last1=Stiffler | date=2007-07-27  | title=Reef of glass sponges found off Washington's coast | newspaper=[[Seattle Post-Intelligencer]] | url=http://www.seattlepi.com/local/325489_sponge28.html | via=seattlepi.com }}</ref> which are studied by the [[Sponge Reef Project]]. In the case of ''[[Sarostegia oculata]]'', this species almost always hosts symbiotic [[Zoantharia|zoanthids]], which cause the hexactinellid sponge to imitate the appearance and structure of coral reefs.<ref name=":02">{{cite journal |last1=Hajdu |first1=Eduardo |last2=Castello-Branco |first2=Cristiana |last3=Lopes |first3=Daniela A. |last4=Sumida |first4=Paulo Yukio Gomes |last5=Perez |first5=Jose Angel Alvarez |date=December 2017 |title=Deep-sea dives reveal an unexpected hexactinellid sponge garden on the Rio Grande Rise (SW Atlantic). A mimicking habitat? |journal=Deep Sea Research Part II: Topical Studies in Oceanography |volume=146 |pages=93–100 |doi=10.1016/j.dsr2.2017.11.009 |bibcode=2017DSRII.146...93H |url=https://linkinghub.elsevier.com/retrieve/pii/S0967064517304149 |lang=en |url-access=subscription }}</ref> Only 33&nbsp;species of this sponge were reported in the South Atlantic until 2017 when the submersible ''Shinka&nbsp;6500'' went on an expedition through the Rio Grande Rise.<ref name=":02"/> Reefs discovered in [[Hecate Strait]], British Columbia, have grown to up to {{convert|7|km|mi nmi}} long and {{convert|20|m|0|abbr=off}} high. Prior to these discoveries, sponge reefs were thought to have died out in the [[Jurassic]] period.<ref>{{cite news |title=B.C.'s reefs among science's great finds |date=2005-02-24 |work=Georgia Straight Vancouver's News & Entertainment Weekly |url=https://www.straight.com/article/b-c-s-reefs-among-sciences-great-finds |via=straight.com |access-date=2017-05-22 |lang=en }}</ref><ref>{{Cite news|url=http://www.cbc.ca/radio/quirks/diving-deep-for-glass-sponges-1.4124452?autoplay=true|title=Diving deep for glass sponges |publisher=[[CBC Radio]]|access-date=2017-05-22|language=en}}</ref>

Reports of glass sponges have also been recorded on the wrecks of {{HMCS|Saskatchewan|DDE 262|6}} and {{HMCS|Cape Breton|ARE 100|6}} off the coast of [[Vancouver Island]]. Species of zoantharin that rely on hexactinellids have also been found off the coast of the Japanese island of [[Minamitorishima]] (Marcus Island). Unidentified species of zoanthids have also been found in [[Australia]]n waters; if these are identified as the same as the ones found in Minamitorishima, it could be evidence of hexactinellids existing in all of the Pacific Ocean.<ref>{{cite journal |last1=Kise |first1=Hiroki |last2=Nishijima |first2=Miyuki |last3=Iguchi |first3=Akira |last4=Minatoya |first4=Junpei |last5=Yokooka |first5=Hiroyuki |last6=Ise |first6=Yuji |last7=Suzuki |first7=Atsushi |date=2023-03-24 |title=A new hexactinellid-sponge-associated zoantharian (Porifera, Hexasterophora) from the northwestern Pacific Ocean |journal=ZooKeys |issue=1156 |pages=71–85 |doi=10.3897/zookeys.1156.96698 |doi-access=free |issn=1313-2970 |pmc=10208231 |pmid=37234793 |bibcode=2023ZooK.1156...71K }}</ref>

== Conservation ==
Most hexactinellids live in deep waters that are not impacted by human activities. However, there are glass-sponge reefs off the coast of British Columbia. The Canadian government designated {{convert|2,140|km2|0}} of the [[Hecate Strait]] and [[Queen Charlotte Sound (Canada)|Queen Charlotte Sound]] as the [[Hecate Strait and Queen Charlotte Sound Glass Sponge Reefs Marine Protected Area]]. This area contains four glass sponge reefs. The new regulations prohibit bottom-contact fishing within {{convert|200|m|0}} of the sponge reefs.<ref>{{Cite web |last=Government of Canada |first=Fisheries and Oceans Canada |date=2019-09-18 |title=Hecate Strait/Queen Charlotte Sound Glass Sponge Reefs Marine Protected Area (HS/QCS MPA) |url=https://www.dfo-mpo.gc.ca/oceans/mpa-zpm/hecate-charlotte/index-eng.html |access-date=2023-10-06 |website=www.dfo-mpo.gc.ca}}</ref> Although human activities only affect a small portion of glass sponges, they are still subject to the threat of climate change. Experiments using the species ''[[Aphrocallistes vastus]]'' have shown that increases in temperature and acidification can lead to weakened skeletal strength and stiffness.<ref>{{Cite journal |last1=Stevenson |first1=A. |last2=Archer |first2=S. K. |last3=Schultz |first3=J. A. |last4=Dunham |first4=A. |last5=Marliave |first5=J. B. |last6=Martone |first6=P. |last7=Harley |first7=C. D. G. |date=2020-05-18 |title=Warming and acidification threaten glass sponge Aphrocallistes vastus pumping and reef formation |journal=Scientific Reports |language=en |volume=10 |issue=1 |pages=8176 |doi=10.1038/s41598-020-65220-9 |pmid=32424237 |pmc=7235243 |bibcode=2020NatSR..10.8176S |issn=2045-2322}}</ref> In 1995, an Antarctic ice shelf collapsed due to climate change. Since then, studies of the area have shown that hexactinellid reefs have been increasing in size despite the changes in climate.<ref>{{Cite journal |last1=Fillinger |first1=Laura |last2=Janussen |first2=Dorte |last3=Lundalv |first3=Tomas |last4=Richter |first4=Claudio |date=July 22, 2013 |title=Rapid glass sponge expansion after climate-induce Antarctic ice shelf collapse |journal=Current Biology |volume=23 |issue=14 |pages=1330–1334 |doi=10.1016/j.cub.2013.05.051 |pmid=23850279 |s2cid=18142746 |doi-access=free |bibcode=2013CBio...23.1330F }}</ref>

==Evolution and taxonomy==
The earliest known hexactinellids are from the earliest [[Cambrian]] or late [[Neoproterozoic]] eras; ''[[Helicolocellus]]'' is a possible hexactinellid relative from the late [[Ediacaran]].<ref name="Wang2024">{{cite journal |doi=10.1038/s41586-024-07520-y |title=A late-Ediacaran crown-group sponge animal |date=2024 |last1=Wang |first1=Xiaopeng |last2=Liu |first2=Alexander G. |last3=Chen |first3=Zhe |last4=Wu |first4=Chengxi |last5=Liu |first5=Yarong |last6=Wan |first6=Bin |last7=Pang |first7=Ke |last8=Zhou |first8=Chuanming |last9=Yuan |first9=Xunlai |last10=Xiao |first10=Shuhai |journal=Nature |volume=630 |issue=8018 |pages=905–911 |pmid=38839967 |bibcode=2024Natur.630..905W }}</ref> They are fairly common relative to [[demosponges]] as fossils, but this is thought to be, at least in part, because their spicules are sturdier than [[spongin]] and fossilize better. Like almost all sponges, the hexactinellids draw water in through a series of small pores by the whip-like beating of a series of hairs or [[Flagellum|flagella]] in chambers which in this group line the sponge wall.

The class is divided into two subclasses and several orders:<ref>{{cite WoRMS|title=Hexactinellida|22612|url=https://www.marinespecies.org/aphia.php?p=taxdetails&id=22612}}</ref>

Class '''Hexactinellida'''
*Subclass [[Amphidiscophora]]
**Order [[Amphidiscosida]]
**Order †[[Hemidiscosa]]<ref name=":0">''Treatise on Invertebrate Paleontology'' Part E, Revised. Porifera, Volume 3:  Classes Demospongea, Hexactinellida, Heteractinida & Calcarea, xxxi + 872 p., 506 fig., 1 table, 2004, available [https://journals.ku.edu/InvertebratePaleo/issue/view/455 here].  {{ISBN|0-8137-3131-3}}.</ref>
**Order †[[Reticulosa]]<ref name=":0" />
*Subclass [[Hexasterophora]]
**''[[Incertae sedis]]''
***[[Dactylocalycidae]] <small>Gray, 1867</small>
**Order [[Lychniscosida]]
**Order [[Lyssacinosida]]
**Order [[Sceptrulophora]]

==See also==
* [[Sponge reef]]
* [[Cloud sponge]]
* [[Sponge Reef Project]]
* [[Spongicolidae|Glass sponge shrimp]]

==References==
{{reflist|25em}}

== External links ==
* {{Commons category-inline|Hexactinellida}}
* {{Wikispecies-inline|Hexactinellida}}

{{Porifera}}
{{Animalia}}
{{Taxonbar|from=Q263211}}

*{{Cite journal|last1=Falcucci|first1=Giacomo|last2=Amati|first2=Giorgio|last3=Fanelli|first3=Pierluigi|last4=Krastev|first4=Vesselin K.|last5=Polverino|first5=Giovanni|last6=Porfiri|first6=Maurizio|last7=Succi|first7=Sauro|date=July 2021|title=Extreme flow simulations reveal skeletal adaptations of deep-sea sponges|url=https://www.nature.com/articles/s41586-021-03658-1|journal=Nature|language=en|volume=595|issue=7868|pages=537–541|doi=10.1038/s41586-021-03658-1|pmid=34290424|s2cid=236176161|issn=1476-4687|arxiv=2305.10901|bibcode=2021Natur.595..537F }}

[[Category:Hexactinellida| ]]
[[Category:Extant Cambrian first appearances]]