class chondrichtyes group 4

Chondrichtyes

They are cartilaginous Fishes Jawed Fishes Paired Fins Paired Nares

Sharks, Skates, Rays amd Chimaeras

Chondrichtyes

Elasmobranchii (sharks, rays and skates) and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class).

Skeleton

The skeleton is cartilaginous. The notochord, which is present in the young, is gradually replaced by cartilage. They lack ribs, so if they leave water, the larger species' own body weight would crush their internal organs long before they suffocate.

As they do not have bone marrow, red blood cells are produced in the spleen and the epigonal organ (special tissue around the gonads, which is also thought to play a role in the immune system). They are also produced in the Leydig's organ which is only found in cartilaginous fishes, although some do not possess it. The subclass Holocephali, which is a very specialized group, lacks both the Leydig's and epigonal organ.

Appendages

 Tough skin is covered with dermal teeth also called placoid scales or dermal denticles, making it feel like sandpaper. In most species, all dermal denticles are oriented in one direction, making the skin feel very smooth if rubbed in one direction and very rough if rubbed in the other. Another exception are the electric rays, which have a thick and flabby body, with soft, loose skin devoid of dermal denticles and thorns.

Originally the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. In later forms, each pair of fins became ventrally connected in the middle when scapulocoracoid and pubioischiadic bars evolved. In rays, the pectoral fins have connected to the head and are very flexible.

One of the primary characteristics present in most sharks is the heterocercal tail, which aids in locomotion.

Respiration

All Chondrichthyes breathe through 5-7 gills, depending on the species.

A spiracle is a small hole found behind each eye. These can be tiny and circular.

Scoliodon palasorrahHead Region

EYE

SPIRACLE

GILLSNOSTRIL

MOUTH

SNOUT

Functions

Eyes well-adapted to the marine environment

tapetum lucidum- allows them to contract and dilate their

pupils- Located behind the retina, reflects light

back to it, increasing visibility in darknessSome species have nictitating membranes

for eye protection, some roll their eyes back to protect them while striking prey

Nostril

Very keen olfactory senses Some species can detect as little as 1

ppm of blood in seawater Can determine direction of a given smell

through timing of scent detection

Spiracle

Provides oxygenated water directly to the eye and brain through a separate blood vessel

Allows breathing even when buried or lying at the bottom of the ocean

Vestigial/not present in larger, faster moving sharks, present in bottom-dwelling sharks

Respiration

Extracts oxygen as water passes through its gills

While sharks move, water passes through the gills and mouth

Some sharks have lost the ability to pump water through their gills and must move continuously

Gills

Usually 5-7 pairs of slits present at the sides of their heads

No gill covers Filter-feeding sharks expell water

through their gills

Mouth

Have different kinds of teeth according to diet Crustaceans feeders have flat teeth for

crushing Fish feeders have triangular upper teeth

for cutting and pointed lower teeth for gripping

Plankton feeders have teeth for filtering, or reduced teeth

Teeth are arranged in multiple lines in a row

Presence of a tongue-like structure called the basihyal – a thick, cartilaginous structure on the floor of the mouth

Useless for most sharks

Snout

Cartilaginous and spongy, to resist impact caused by chasing after prey

External Features of a Dog Shark

Lateral line canalFin SpinePectoral FinPelvic Fin

Lateral line canal

 is a series of fluid-filled canals just below the skin of the head and along the sides of the body

Contains a number of sensory cell called the neuromasts

detecting low-frequency vibrations and directional water flow.

The shark can sense frequencies in the range of 25 to 50 Hz.

Fin Spines

adaptation for defense against predators.

carry a poison secreted by glands at their base

Pectoral fin

located behind the shark's head. extend outward, act like an

airplane's wings to provide the shark with lift and function as a steering mechanism during swimming and to keep the shark from sinking

Pelvic fin

also act as stabilizers. Located between the pectoral and

anal fins Male sharks have modified pelvic

fins called claspers. have a secondary purpose in males

for clasping during mating.

Claspers(male)

Tail Region

main purpose is to stabilize the animal against rolling and to assist in sudden turns.

Fin Spine – defense mechanism.

This type of tail is known as a heterocercal fin.

Divided into two lobes a larger dorsal lobe and smaller ventral lobe.

main purpose is to provide thrust.

Caudal Fin

receives the products of the intestine, the urinary and the genital ducts. The name cloaca, meaning sewer, seems quite appropriate.

Cloaca