Editing Squid (section)

===Buoyancy===
[[File:Cranchiidae sp.jpg|thumb|The body of glass squids ([[Cranchiidae]]) is mainly filled by a transparent [[coelom]] containing [[ammonium]] ions for buoyancy.]]

Unlike nautiloids and cuttlefish which have gas-filled chambers inside their shells which provide buoyancy, and octopuses which live near and rest on the seabed and do not require to be buoyant, many squid have a fluid-filled receptacle, equivalent to the [[swim bladder]] of a fish, in the [[coelom]] or [[connective tissue]]. This reservoir acts as a chemical buoyancy chamber, with the heavy metallic cations typical of seawater replaced by low [[Molecular mass|molecular-weight]] [[ammonium]] ions, a product of excretion. The small difference in density provides a small contribution to buoyancy per unit volume, so the mechanism requires a large buoyancy chamber to be effective. Since the chamber is filled with liquid, it has the advantage over a swim bladder of not changing significantly in volume with pressure. Glass squids in the family [[Cranchiidae]] for example, have an enormous transparent coelom containing ammonium ions and occupying about two-thirds the volume of the animal, allowing it to float at the required depth. About half of the 28 families of squid use this mechanism to solve their buoyancy issues.<ref name=Ruppert/> The family [[Bathyteuthis|Bathyteuthidae]] get their buoyancy from an oily substance found in their liver and around their mantle and head.<ref>{{Cite web|url=https://books.google.com/books?id=_9sBEAAAQBAJ&dq=Bathyteuthidae+oily+substance+liver&pg=PA67|title=Squid|first=Martin|last=Wallen|date=14 October 2020|publisher=Reaktion Books|via=Google Books}}</ref>