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Chondrichthyes - Coggle Diagram
Chondrichthyes
Introduction
-Chondrichthyes (Cartilage fish) together with Osteichthyes (bony fish) known as the jawed fish.
-Most of two classes of jawed fish share certain common features:
-streamlined body shape to swim efficiently.
-body covering of dermal scale or scale- like structures, with very few exceptions.
-Broad tail and other fins, some paired for locomotion.
-Pharyngeal gills as gaseous exchange surface.
-Ectothermic temperature regulations.
-Kidneys to deal with some aspects of excretion and osmoregulation.
-Class Chondrichthyes include sharks, skates, rays and chimaeras.
-All have cartilage skeleton.
-Chimaeras= subclass of their own and though they have cartilage skeleton many of their other characteristics similar to those of Osteichthyes.
-Rest of Chondrichthyes are all in subclass Elasmobranchii. 
Physical characteristics
Definitive features
-Skeleton made entirely up of cartilage, with only some of large species having some bone, particularly as part of their skull.
-Upper jaw not fused to cranium.
-Cartilage provides required support for larger bodies of these animals and enable high degree of flexibility.
-Neutrally buoyant, which is important requirement for swimming animals, enables animal to maintain its position in water column.
Body plan
-Sharks have torpedo shape while skates and rays dorsoventrally flattened.
-Skates generally have dorsal and caudal fin, but rays do not.
Body covering
-Skin of elasmobranchs covered in dermal denticles.
These tiny teeth highly concentrated on sharks with more being added as they grow.
-In the case of skates and rays, denticles present but not as concentrated as in sharks.
-denticles provide degree of protection but more important as they provide hydrodynamic surface allowing water to flow across skin of sharks with very little drag.
- Also creates a partial exoskeleton for sharks which muscles can act against as they swim.
-It also discourages attachment of parasites.
-Colour and pattern of sharks skin helps with camouflage and they generally have countershading.
Locomotion
-Fins fleshy and covered with skin, strengthened by rods of cartilage and operated by muscles within body.
Sharks
-Tail or caudal fins= primary source of propulsion, asymmetrically arranged around central plane, with most of surface below vertebral column, to provide extra lift which aids as sharks have slightly negative buoyancy.
-Two dorsal fins provide stability along with anal fin.
-paired pectoral and pelvic fins enable direction changes in horizontal and vertical plane.
Skates and rays
-Pectoral fins, have extended to form wing- like structures, good adaptation for moving close to sea floor, where these fish scavenge for dead or burrowing animals with downward facing mouth.
-Neutral buoyancy maintained through cartilage skeleton, large oil-filled liver, and by swallowing air into gut at surface.
-Most still slightly negatively buoyant and will sink slowly if they stop moving forward.
Nervous coordination
-Have well developed brain and very good senses, all of which work together in order for them to survive and find food.
-Eyes: Pupils can construct and dilate to control amount of incoming light, allowing sharks to focus clearly on strongly contrasted objects, bony fish do not have this adaptation.
-Tapetum present, layer in eyes which reflects light and enables better although slightly blurred vision in dark conditions.
-Most sharks seem to be color blind.
-Nasal pouches- nostrils on the rostrum, enable water to flow through, as shark moves forward.
Lined with chemosensitive olfactory cells able to detect tiny amounts of substances like blood or rotting flesh.