Chordates
By Samuel Davis
-Vertebrates are in the phylum
Introduction:
Chordate(containing the spinal cord)
3 Characteristics of Vertebrates within life
histories:
• Vertebrates first evolved in the ocean.
• The invertebrate ancestors of vertebrates
had gill slits, but these were used primarily for
filter feeding; these organisms took up most of
the oxygen they needed through the skin.
• Vertebrates are found from the tropics to the
polar regions, from the deep sea to high
mountains, and even the air.
Reproduction in beings of the
phylum Chordata is sexual, with
the exception of urochordates that
Sexual
can also reproduce asexually. In
Reproduction
some classes (cyclostomes,
osteichthyes fishes and
amphibians) there is larval stage.
Sexual
Reproduction
cont.
With rare exceptions,
fishes, amphibians,
reptiles and monotreme mammals are
oviparous, egg-laying (embryos develop
within eggs and outside the mother’s
body) and marsupial and placental
mammals are viviparous (embryos develop
inside the mother’s body, feeding from
her).
Evolution
All chordate evolved from
a basic eukaryote with a
Timeline
spine.
Different classes of
Marine Chordate
Jawless fish
Cartilaginous fish
Bony fish
Jawless Fish
Lamprey
Hagfish
Hagfish, (also known
Lampreys (sometimes
as Hyperotreti), are eelalso called lamprey eels)
shaped slime-producing
are an order of jawless
marine animals
fish-like vertebrates,
(occasionally called slime
whose adults are
eels). They are the only
characterized by a
known living vertebrates
toothed, funnel-like
that have a skull but not a
sucking mouth.
vertebral column.
Chondrichthyes or cartilaginous
fishes are jawed fish with paired fins,
Chondricthyes
paired nares, scales, a heart with its chambers
in series, and skeletons made
of cartilage rather than bone. The class is
divided into two
subclasses: Elasmobranchii (sharks, rays and s
kates) and Holocephali (chimaeras,
sometimes called ghost sharks, which are
sometimes separated into their own class).
The skeleton is cartilaginous.
Their tough skin is covered with dermal
Chondricthyes
teeth (again with Holocephali as an
exception as the teeth are lost in adults, only
kept on the clasping organ seen on the front
of the male's head), also called placid scales
or dermal denticles, making it feel like
sandpaper.
All Chondrichthyes breathe through 57 gills, depending on the species.
Fertilization is internal.
Development is usually live birth
Chondricthyes
Reproduction
(ovoviviparous species) but can be
through eggs (oviparous). Some
rare species are viviparous. There is
no parental care after birth;
however, some Chondrichthyes do
guard their eggs.
Skates and Rays
Batoids are flat-bodied, and, like sharks, are cartilaginous , meaning
they have a boneless skeleton made of a tough, elastic substance
Most species live on the sea floor, in a variety of geographical regions —
many in coastal waters, few live in deep waters to at least 3,000 meters
(9,800 ft)
Batoids reproduce in a number of ways. As is characteristic of
elasmobranches, batoids undergo internal fertilization. Internal
fertilization is advantageous to batoids as it conserves sperm, does not
expose eggs to consumption by predators, and ensures that all the energy
involved in reproduction is retained and not lost to the environment.
Chondricthyes
Shark teeth are embedded in the gums rather than directly affixed to
the jaw, and are constantly replaced throughout life.
Multiple rows of replacement teeth grow in a groove on the inside of the
jaw and steadily move forward in comparison to a conveyor belt;
 some sharks lose 30,000 or more teeth in their lifetime.
The rate of tooth replacement varies from once every 8 to 10 days to
several months.
Shark skeletons are very different from those of bony
fish and vertebrates.
Cartilage is flexible and durable, yet is about half the normal density of
bone.
This reduces the skeleton’s weight, saving energy.
Because sharks do not have rib cages, they can easily be crushed under
their own weight on land.
Sharks
Like other fish, sharks extract oxygen from seawater as it passes over
their gills. Unlike other fish, shark gill slits are not covered, but lie in a
row behind the head. A modified slit called a spiracle lies just behind
the eye, which assists the shark with taking in water
during respiration and plays a major role in bottom–dwelling sharks.
Digestion
can take a long time.
Unwanted items never get past the stomach, and instead the shark
either vomits or turns its stomachs inside out and ejects unwanted
items from its mouth.
Smell:
Sharks have the ability to determine the direction of a given scent based on the timing of scent
detection in each nostril.
This is similar to the method mammals use to determine direction of sound.
They are more attracted to the chemicals found in the intestines of many species, and as a result often
linger near or in sewage outfalls.
Some species, such as nurse sharks, have external barbells that greatly increase their ability to sense
prey.
Sight:
Shark eyes are similar to the eyes of other vertebrates, including similar lenses, corneas and retinas,
 their eyesight is well adapted to the marine environment. T
this means that sharks can contract and dilate their pupils, like humans, something no other fish can
do.
This tissue is behind the retina and reflects light back to it, thereby increasing visibility in the dark
waters.
Hearing:
Although it is hard to test sharks' hearing, they may have a sharp sense of hearing and can possibly hear
prey many miles away.
A small opening on each side of their heads (not the spiracle) leads directly into the inner ear through a
thin channel
Senses
FEEDING
 Most sharks are carnivorous.
 Basking sharks, whale sharks, and mega mouth
sharks have independently evolved different
strategies for filter feeding plankton:
 basking sharks practice ram feeding,
 whale sharks use suction to take in plankton
and small fishes
 mega mouth sharks make suction feeding more
efficient by using the tissue inside of their
mouths to attract prey in the deep ocean
Other highly specialized feeders include cookie cutter sharks, which
feed on flesh sliced out of other larger fish and marine mammals.
Cookie cutter teeth are enormous compared to it’s size.
Feeding
Cont
Although
they have never been observed feeding, they are believed to
latch onto their prey and use their thick lips to make a seal, twisting
their bodies to rip off flesh.
Many sharks, including the white tip reef shark are cooperative
feeders and hunt in packs to herd and capture elusive prey.
These social sharks are often migratory, traveling huge distances
around ocean basins in large schools.
These migrations may be partly necessary to find new food sources.
The End