Editing Earless seal (section)

===External anatomy===

[[File:Harbor seal with skeleton GS.jpg|thumb|Skeletal anatomy of a harbor seal. 1. Skull. 2. Spine. 3. Tail. 4. Hindlimb. 5. Forelimb. 6. Shoulder. 7. Pelvis. 8. Rib cage.]]
[[File:Phoca vitulina 02 MWNH 1464.JPG|thumb|left|[[Harbor seal]] skull (''Phoca vitulina'')]]

Adult phocids vary from {{convert|1.17|m|ft|abbr=on}} in length and {{convert|45|kg|lb|abbr=on}} in weight in the [[ringed seal]] to {{convert|5.8|m|ft|abbr=on}} and {{convert|4000|kg|lb|abbr=on}} in the [[southern elephant seal]], which is the largest member of the order [[Carnivora]]. Phocids have fewer teeth than land-based members of the [[Carnivora]], although they retain powerful [[canine tooth|canines]]. Some species lack [[Molar (tooth)|molar]]s altogether. The [[dentition|dental formula]] is:
{{DentalFormula|upper=2–3.1.4.0–2|lower=1–2.1.4.0–2}}

While otariids are known for speed and maneuverability, phocids are known for efficient, economical movement. This allows most phocids to forage far from land to exploit prey resources, while otariids are tied to rich [[upwelling]] zones close to breeding sites. Phocids swim by sideways movements of their bodies, using their hind flippers to fullest effect.<ref name=EoM>{{cite book|editor= Macdonald, D.|author= McLaren, Ian|year= 1984|title= The Encyclopedia of Mammals|publisher= Facts on File|location= New York|pages= [https://archive.org/details/encyclopediaofma00mals_0/page/270 270–275]|isbn= 978-0-87196-871-5|url-access= registration|url= https://archive.org/details/encyclopediaofma00mals_0/page/270}}</ref> Their fore flippers are used primarily for steering, while their hind flippers are bound to the [[pelvis]] in such a way that they cannot bring them under their bodies to walk on them. They are more streamlined than fur seals and sea lions, so they can swim more effectively over long distances. However, because they cannot turn their hind flippers downward, they are very clumsy on land, having to wriggle with their front flippers and abdominal [[muscle]]s.

[[File:Seal kidney-- FMVZ USP-08.jpg|thumb|Seal kidney]]

Phocid respiratory and circulatory systems are adapted to allow diving to considerable depths, and they can spend a long time underwater between breaths. Air is forced from the [[lung]]s during a dive and into the upper respiratory passages, where gases cannot easily be absorbed into the bloodstream. This helps protect the seal from [[Decompression sickness|the bends]]. The [[middle ear]] is also lined with blood sinuses that inflate during diving, helping to maintain a constant pressure.<ref name=EoM/>

Phocids are more specialized for [[Aquatic animal|aquatic]] life than otariids. They lack external ears and have sleek, streamlined bodies. Retractable [[nipple]]s, internal [[testicle]]s,<ref name="PerrinWürsig2009">{{cite book|author1=Perrin, William F. |author2=Würsig, Bernd |author3= Thewissen, J.G.M.|title=Encyclopedia of Marine Mammals|url=https://books.google.com/books?id=2rkHQpToi9sC&q=phocid+OR+phocidae|date=2009|publisher=Academic Press|isbn=978-0-08-091993-5}}</ref> and an internal [[penile sheath]] provide further streamlining. A smooth layer of [[blubber]] lies underneath the skin. Phocids are able to divert [[blood]] flow to this layer to help control their temperatures.<ref>{{Cite journal|last1=Favilla|first1=Arina B.|last2=Costa|first2=Daniel P.|date=2020-09-11|title=Thermoregulatory Strategies of Diving Air-Breathing Marine Vertebrates: A Review|journal=Frontiers in Ecology and Evolution|volume=8|pages=555509|doi=10.3389/fevo.2020.555509|issn=2296-701X|doi-access=free}}</ref>