class chondrichtyes group 4
Post on 03-Jun-2015
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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
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