Editing Cartilage (section)

=== Invertebrate cartilage ===
Cartilage tissue can also be found among some arthropods such as [[horseshoe crab]]s, some mollusks such as marine [[snail]]s and [[cephalopod]]s, and some annelids like sabellid polychaetes.

====Arthropods====
The most studied cartilage in arthropods is the branchial cartilage of ''[[Limulus polyphemus]]''. It is a vesicular cell-rich cartilage due to the large, spherical and vacuolated chondrocytes with no homologies in other arthropods. Other type of cartilage found in ''L.&nbsp;polyphemus'' is the endosternite cartilage, a fibrous-hyaline cartilage with chondrocytes of typical morphology in a fibrous component, much more fibrous than vertebrate hyaline cartilage, with [[mucopolysaccharide]]s immunoreactive against chondroitin sulfate antibodies. There are homologous tissues to the endosternite cartilage in other arthropods.<ref name="ColeHall2004">{{cite journal | vauthors = Cole AG, Hall BK | title = The nature and significance of invertebrate cartilages revisited: distribution and histology of cartilage and cartilage-like tissues within the Metazoa | journal = Zoology | volume = 107 | issue = 4 | pages = 261–73 | year = 2004 | pmid = 16351944 | doi = 10.1016/j.zool.2004.05.001 | bibcode = 2004Zool..107..261C }}</ref> The embryos of ''Limulus polyphemus'' express ColA and hyaluronan in the gill cartilage and the endosternite, which indicates that these tissues are fibrillar-collagen-based cartilage. The endosternite cartilage forms close to Hh-expressing ventral nerve cords and expresses ColA and SoxE, a Sox9 analog. This is also seen in gill cartilage tissue.<ref name="TarazonaEtAl2016">{{cite journal | vauthors = Tarazona OA, Slota LA, Lopez DH, Zhang G, Cohn MJ | title = The genetic program for cartilage development has deep homology within Bilateria | journal = Nature | volume = 533 | issue = 7601 | pages = 86–9 | date = May 2016 | pmid = 27111511 | doi = 10.1038/nature17398 | bibcode = 2016Natur.533...86T | s2cid = 3932905 }}</ref>

====Mollusks====
In cephalopods, the models used for the studies of cartilage are ''[[Octopus vulgaris]]'' and ''[[Sepia officinalis]]''. The cephalopod cranial cartilage is the invertebrate cartilage that shows more resemblance to the vertebrate hyaline cartilage. The growth is thought to take place throughout the movement of cells from the periphery to the center. The chondrocytes present different morphologies related to their position in the tissue.<ref name="ColeHall2004" />
The embryos of ''S.&nbsp;officinalis'' express ColAa, ColAb, and hyaluronan in the cranial cartilages and other regions of chondrogenesis. This implies that the cartilage is fibrillar-collagen-based. The ''S.&nbsp;officinalis'' embryo expresses hh, whose presence causes ColAa and ColAb expression and is also able to maintain proliferating cells undiferentiated. It has been observed that this species presents the expression SoxD and SoxE, analogs of the vertebrate Sox5/6 and Sox9, in the developing cartilage. The cartilage growth pattern is the same as in vertebrate cartilage.<ref name="TarazonaEtAl2016" />

In gastropods, the interest lies in the [[odontophore]], a cartilaginous structure that supports the radula. The most studied species regarding this particular tissue is ''[[Busycotypus canaliculatus]]''. The odontophore is a vesicular cell rich cartilage, consisting of vacuolated cells containing myoglobin, surrounded by a low amount of extra cellular matrix containing collagen. The odontophore contains muscle cells along with the chondrocytes in the case of ''[[Lymnaea]]'' and other mollusks that graze vegetation.<ref name="ColeHall2004" />

====Sabellid polychaetes====
The [[Sabellidae|sabellid polychaetes]], or feather duster worms, have cartilage tissue with cellular and matrix specialization supporting their tentacles. They present two distinct extracellular matrix regions. These regions are an acellular fibrous region with a high collagen content, called cartilage-like matrix, and collagen lacking a highly cellularized core, called osteoid-like matrix. The cartilage-like matrix surrounds the osteoid-like matrix. The amount of the acellular fibrous region is variable. The model organisms used in the study of cartilage in sabellid polychaetes are ''Potamilla'' species and ''[[Myxicola infundibulum]]''.<ref name="ColeHall2004" />