Editing Anatomy (section)

=== Fish anatomy ===
{{main|Fish anatomy}}
[[File:Internal anatomy of a fish (cutaway diagram).jpg|thumb|left|Cutaway diagram showing various organs of a fish]]
The body of a [[fish]] is divided into a head, trunk and tail, although the divisions between the three are not always externally visible. The skeleton, which forms the support structure inside the fish, is either made of cartilage, in [[cartilaginous fish]], or bone in [[bony fish]]. The main skeletal element is the vertebral column, composed of articulating [[vertebra]]e which are lightweight yet strong. The ribs attach to the spine and there are no [[Limb (anatomy)|limbs]] or limb girdles. The main external features of the fish, the [[fish fin|fins]], are composed of either bony or soft spines called rays, which with the exception of the [[caudal fin]]s, have no direct connection with the spine. They are supported by the muscles which compose the main part of the trunk.<ref name=Dorit818/> The heart has two chambers and pumps the blood through the respiratory surfaces of the [[gill]]s and on round the body in a single circulatory loop.<ref>{{cite web|url=https://library.thinkquest.org/C003758/Development/fish.htm |title=The fish heart |work=ThinkQuest |publisher=Oracle |access-date=27 June 2013 |url-status=dead |archive-url=https://web.archive.org/web/20120428001536/https://library.thinkquest.org/C003758/Development/fish.htm |archive-date=28 April 2012 }}</ref> The eyes are adapted for seeing underwater and have only local vision. There is an inner ear but no external or [[middle ear]]. Low frequency vibrations are detected by the [[lateral line]] system of sense organs that run along the length of the sides of fish, and these respond to nearby movements and to changes in water pressure.<ref name=Dorit818>{{cite book |title=Zoology |url=https://archive.org/details/zoology0000dori |url-access=registration |last1=Dorit |first1=R. L. |last2=Walker |first2=W. F. |last3=Barnes |first3=R. D. |year=1991 |publisher=Saunders College Publishing |isbn=978-0-03-030504-7 |pages=[https://archive.org/details/zoology0000dori/page/816 816–818] }}</ref>

Sharks and rays are [[Basal (phylogenetics)|basal]] fish with numerous [[Primitive (phylogenetics)|primitive]] anatomical features similar to those of ancient fish, including skeletons composed of cartilage. Their bodies tend to be dorso-ventrally flattened, they usually have five pairs of gill slits and a large mouth set on the underside of the head. The dermis is covered with separate dermal [[placoid scales]]. They have a [[cloaca]] into which the urinary and genital passages open, but not a [[swim bladder]]. Cartilaginous fish produce a small number of large, [[Egg yolk|yolky]] eggs. Some species are [[ovoviviparous]] and the young develop internally but others are [[oviparous]] and the larvae develop externally in egg cases.<ref name=Kotpal>{{cite book |title=Modern Text Book of Zoology: Vertebrates |last=Kotpal |first=R. L. |year=2010 |publisher=Rastogi Publications |isbn=978-81-7133-891-7 |page=193 |url=https://books.google.com/books?id=U7N1j-8LMsEC&pg=PA199 }}</ref>

The bony fish lineage shows more [[Derived trait|derived]] anatomical traits, often with major evolutionary changes from the features of ancient fish. They have a bony skeleton, are generally laterally flattened, have five pairs of gills protected by an [[operculum (fish)|operculum]], and a mouth at or near the tip of the snout. The dermis is covered with overlapping [[Fish scale|scales]]. Bony fish have a swim bladder which helps them maintain a constant depth in the water column, but not a cloaca. They mostly [[Spawn (biology)|spawn]] a large number of small eggs with little yolk which they broadcast into the water column.<ref name=Kotpal/>