Hexasterophora

{{Short description|Subclass of Hexactinellid sponges}}

{{More citations needed|type=animal|date=December 2009}}

{{Automatic taxobox

| fossil_range = {{fossil range | Ordovician | Recent | refs = {{Cite Q|Q111529763|last1=Botting |first1=J. P. |last2=Janussen |first2=D. |last3=Muir |first3=L. A. |last4=Dohrmann |first4=M. |last5=Ma |first5=J. |last6=Zhang |first6=Y.}}}}

| image = Haeckel Hexactinellae.jpg

| image_caption =

| taxon = Hexasterophora

| authority = Schulze, 1886

| subdivision_ranks = Subgroups

| subdivision = * Order Lychniscosida

• Order Lyssacinosida
• Order Sceptrulophora
• incertae sedis
• Family Dactylocalycidae

| synonyms = * Aulocalycoida Tabachnick & Reiswig, 2000{{cite web |title=WoRMS - World Register of Marine Species - Aulocalycoida |url=https://www.marinespecies.org/aphia.php?p=taxdetails&id=171606 |website=www.marinespecies.org |access-date=11 June 2021}}

• Hexactinosida Schrammen, 1912 {{cite web |title=WoRMS - World Register of Marine Species - Hexactinosida |url=https://www.marinespecies.org/aphia.php?p=taxdetails&id=171628 |website=www.marinespecies.org |access-date=11 June 2021 |language=en}}

}}

File:Hexactinellida diversity.png (order Lyssacinosida, C), Lefroyella (order Sceptrulophora, D), and a hexaster microsclere (A, left) in a collage of hexactinellids.]]

Hexasterophora are a subclass of glass sponges in the class Hexactinellida. Most living hexasterophorans can be divided into three orders: Lyssacinosida, Lychniscosida, and Sceptrulophora.{{Cite journal |last1=Dohrmann |first1=Martin |last2=Janussen |first2=Dorte |last3=Reitner |first3=Joachim |last4=Collins |first4=Allen G. |last5=Wörheide |first5=Gert |date=2008 |editor-last=Anderson |editor-first=Frank |title=Phylogeny and Evolution of Glass Sponges (Porifera, Hexactinellida) |journal=Systematic Biology |language=en |volume=57 |issue=3 |pages=388–405 |doi=10.1080/10635150802161088 |issn=1076-836X|doi-access=free |pmid=18570034 }} Like other glass sponges, hexasterophorans have skeletons composed of overlapping six-rayed spicules. In addition, they can be characterized by the presence of hexasters, a type of microsclere (microscopic spicules) with six rays unfurling into multi-branched structures.{{Cite journal |last1=Łukowiak |first1=Magdalena |last2=Van Soest |first2=Rob |last3=Klautau |first3=Michelle |last4=Pérez |first4=Thierry |last5=Pisera |first5=Andrzej |last6=Tabachnick |first6=Konstantin |date=2022 |title=The terminology of sponge spicules |url=https://onlinelibrary.wiley.com/doi/10.1002/jmor.21520 |journal=Journal of Morphology |language=en |volume=283 |issue=12 |pages=1517–1545 |doi=10.1002/jmor.21520 |pmid=36208470 |issn=0362-2525|url-access=subscription }}

A living sponge is commonly firmly attached by its base to a hard substratum; less often rooted by the anchoring spicules and rarely inserted directly into the loose bottom sediments.

The three orders are differentiated by the extent to which adjacent spicules have fused. The oldest order, without fused spicules, is Lyssacinosida (or Lyssacinosa), which appears in the Ordovician. The other two orders have fully fused their spicules into a framework of dictyonal strands. The most fused order is Lychniscosida (or Lychniscosa), which develops octahedral frames (lychniscs) around the nodes between their dictyonal strands. Lychniscosa fossils first appeared in the Middle Jurassic.{{Cite journal |last=Pisera |first=A |date=2006-02-01 |title=Palaeontology of sponges — a review |url=http://www.nrcresearchpress.com/doi/10.1139/z05-169 |journal=Canadian Journal of Zoology |language=en |volume=84 |issue=2 |pages=242–261 |doi=10.1139/z05-169 |bibcode=2006CaJZ...84..242P |issn=0008-4301|url-access=subscription }}{{Citation |last=Krautter |first=Manfred |title=Fossil Hexactinellida: An Overview |date=2002 |url=http://link.springer.com/10.1007/978-1-4615-0747-5_124 |work=Systema Porifera |pages=1211–1223 |editor-last=Hooper |editor-first=John N. A. |access-date=2023-05-02 |place=Boston, MA |publisher=Springer US |language=en |doi=10.1007/978-1-4615-0747-5_124 |isbn=978-0-306-47260-2 |editor2-last=Van Soest |editor2-first=Rob W. M. |editor3-last=Willenz |editor3-first=Philippe|url-access=subscription }}

Sponges intermediate between these two extremes were historically placed into the order Hexactinosa (or Hexactinosida). Genetic sequencing has determined that this proposed order is polyphyletic, with its constituents split between the valid order Sceptrulophora (bearing sceptrules) and the family Dactylocalycidae (lacking sceptrules). The oldest "hexactinosan" fossils are from the Devonian.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}}.