CHONDRICTHYES Group VI

Mercado, Felix, Reyes, Repurido, Bada,

Chondros’’ - Cartilages “Ichthyos’’ - Fish

Cartilaginous fishes (Chondrichthyes)

are a group of vertebrates that

Includes sharks, rays, skates and

chimaeras.

fossil record about 420 million years ago during the Devonian Period. 

The earliest known cartilaginous fishes were ancient sharks that were descended from bony-skeleton placoderms. These primitive sharks are older than the dinosaurs.

They swam in the world’s oceans 420 million years ago, 200 million years before the first dinosaurs appeared on land.

Cartilagenous fishes characterized by:

• paired nostrils

• skeleton completely cartilagenous with no endoskeletal bone

• no swim bladder

• gill arches internal to gills

• Possess movable jaws that usually have teeth

• Mouth is ventral, underneath the head

• scales dermal placoid when present

• Paired lateral fins

Skates & Rays• Flattened bodies

• Dermersal – live on the bottom• Gill slits on the ventral side (bottom)• Pectoral fins are flat and expanded• Head fuses with pectoral fins with

eyes on top

Ratfish / Chimaeras• Gill slits covered by

a flap of skin• Mostly deep-water

fish• Eat crustaceans and

mollusks

Most cartilaginous fishes live in

marine habitats all their lives,

but a few species of sharks and

rays live in freshwater during all

or part of their lives.

sharks: bottom of coastal

waters, open sea-needs: smaller sea animals

to hunt rays:

bottom of saltwater or freshwater

-needs: crustaceas, mullusks, warmwater

Skates and rays * warm temperature seas

Sharks * cold deep * the ocean floor * move towards the coast for

feeding

There are just under 1000 living

species, all of which have

cartilaginous skeletons, even

though they are descended from

ancestors that had bone.

Megalodon

• Ancient shark• Largest predatory fish ever• Twice the size of a great white

Megalodonapproximately 18m long (and with a mass estimated at 50-100 metrics tones) it resembled a massive great white shark and was the top ocean predator of its era.

* Manta Ray(about 30 feet long)

* Basking Shark(about 40 feet long and 19 tons).

 paired fins and flexible bodies making movement in

water very feasible. 

Kingdom : Animalia Phylum : Chordata Subphylum : Vertebrata Infraphylum :Gnathostomata Class : Chondrichthyes Subclass : Elasmobranchii Orders : Cladoselachii,

Pleuracanthodii ( extinct sharks

) Orders : Squaliformes Order : Rajiformes Subclass : Holocephali

External and Internal Structure

Scales

• Scales are very small and sharp• Same composition as the teeth

Jaws

• Made of bone• Contain the disposable teeth• In some species capable of extending jaw out from body

Teeth• Same composition as the scales

• Continually shed and replaced by the rows behind

Body Plan: Chondrichthyes have bodies made of cartilage instead of bone. They also lack ribs. This allows for extreme flexibility. Their bodies are covered in a thick skin. This skin is covered dermal teeth, often called denticles, making it feel like sand paper.

• Coelomate: Chondrichthyes have a coelomate.• Segmentation:

Body segmentation is present, allowing for specialization of body parts

• Symmetry: Chondrichthyes have bilateral symmetry

Skeletal System: Chondrichthyes have a body made of cartilage instead of bone and they do not have ribs or bone marrow.

ENDOSKELETON or EXOSKELETON:

Chondrichthyans have an endoskeleton made completely from cartilage, thus their being called cartilaginous fish.

Digestive System• Very short esophogus

• Stomach can be up to 1/3 the length of the shark

• Intestine is really small, only about a foot

Respiratory System

• Must swim to force water through their gills• Some such as nurse sharks can get enough

oxygen so they do not need to swim

Circulatory System

Heart is Built upon the pattern similar to other fishes. The Heart is consists of a sinus venosus, artrium,

ventricle and conus with three rows of valves.

Nervous System• Lateral line used for sensing vibrations in

the water

• Ampullae of Lorenzini• Jelly filled canals that can detect electrical

fields, magnetic fields, temperature, salinity, water pressure, etc.

TYPE OF NERVOUS SYSTEM:

* Chondrichthyans have myelin sheaths around the axons of their neurons.* This permits much more rapid transmission of nerve impulses.* They also have a single, hollow, ectodermal, dorsal nerve cord with a large anterior end ( which is the brain).

* They have three main sections to their brains, one which in controls ability to smell, another which is responsible for vision, learning, and motor responses, and the last which coordinates movement, muscle tone, and balance.

Reproductive System:Chondrichthyans reproduce by internal fertilizationThis is in order to protect young from highly hypertonic environment, since they do not have the ability to survive in the salty water until later

Mating One clasper will rotate 90º and will be inserted

into the female’s cloaca Clasper will expand cartilaginous spurs to

anchor in the female

Importance:

Reference: