Chordates 2BIbDF09 10/11

What are Chordates ?

Chordates from the phylum Chordata are animals that have during the embryonic development a notochord, a hallow dorsal nerve cord, a pharyngeal gill slits, an endostyle and a post-anal tail. This is mainly what differentiate them from the other Phyla. The invertebrates retain most of these features, but the vertebrates see these features evolve into more complex organs.

*see Appendix Chordates 1

What is a dorsal, hollow cord?

The dorsal chord is formed from a part of the echinoderm that rolls, forming the hollow tube. The dorsal nerve chord will become the brain and the spinal cord. Dorsal nerve cord is mainly found in phylum Vertebrata.

What is the notochord?

The notochord is a flexible, rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo.In some chordates,it will be the main axial support of the body, while in most vertebrates it becomes the vertebral body of the vertebral column.

What are the pharyngeal slits or clefts?

In the non-vertebrate chordates (lancelets and tunicates) who lives in an aquatic environment, the pharyngeal are filter feeding. In the vertebrate chordates, the pharyngeal arch give rise to the oral jam which allows the breathing and the feeding. The second arch becomes the hyoid and jaw support. For the fishes, they will contribute the branchial skeleton, which support the gills. In the tetrapods the anterior arches will develop into components of the ear.

What is the muscular, post-anal tail?

The tail is the part of the body that corresponds roughly to the sacrum and coccyx in mammals and birds. The tails are a characteristics of vertebrates, some invertebrates including scorpions and springtail, as well as snails and slugs. It is used like a source of locomotion for the fish or other animal of the marine live and some others species use their tail to stay in balance.

MelanieD 13 février 2011 à 12:52 (CET)

Although this four anatomical characteristics distinguish the chordates from the other animal phyla, they aren't all present during the whole life of all the chordates. For example, the pharyngeal slits are seen only during the embryonic development in most vertebrates and the post-anal tail appears also only during embryo-genesis for the humans( who are chordates too.)NathalieR 17 janvier 2011 à 10:51 (CET)

What are the different kinds of Chordates ?

Invertebrates Chordates

What are invertebrate-chordates?

Phylum Chordata can be divided into the three subphyla. Two of these, Urochordata and Cephalochordata, are nonvertebrate; the third subphylum is Vertebrata. The invertebrate chordates lack vertebrae or other bones, and in the case of the urochordates, their adult form is greatly different from what we expect chordates to look like. There are about 1600 species of tunicates (urochordates), 24 species of lancelets (cephalochordates), and over 50,000 vertebrates.

What are Cephalochordates (or Lancelets)?

Cephalochordates are also called lancelets. They are small, mobile, and blade-like shaped animals with a “fish-like” appearance. As larvae, lancelets develop a notochord, a dorsal, hollow nerve cord, pharyngeal slits, and a post-anal tail. They keep the main chordate characteristics. The most important characteristic preserved as adult is the notochord, where it functions as an endoskeleton. Adult lancelets can be 5 cm long.

How do they feed themselves?

The larvae feed themselves with plaktons present in the water, alternating between upward swimming and passive sinking as the larvae sink, they trap plankton and other suspended particles in their pharynx. Adult cephalochordates feed themselves by suspension feeding. They first swim down to the seafloor and enter backward into the sand until only their head is left out into the water. By doing so, they can now take water in through their mouth with the help of cilia. Then a net of mucus on their pharyngeal gill slits traps food particles as the water passes through the slits, and then the food particles go to the intestine.

How do they move?

The cephalochordates also have a notochord that functions as an endoskeleton. Adult lancelets have large blocks of muscle arranges in a series along the length of the notochord, which proves that lancelets have segmented bodies. By coordinated contraction of the muscles, the notochord flexes, producing side-to-side undulations, which enable them to move forward or backward. These invertebrate chordates display, in a simple form, the swimming mechanism of fishes, but they still spend most of their time buried in the sand.

How do they reproduce themselves?

Lancelets have separate sexes, they are either male or female. The gametes (eggs and sperm) are released into the water, so the fertilization occurs externally.

What are Urochordata (or Tunicates)?

Urochordates are also called tunicates. There are two major sub-lineages: the sea squirts and salps (but we will focus more on sea squirts). The urochordates has an exoskeleton-like coat of polysaccharide, called a tunic, that covers and supports the body; a U-shaped gut; and two body openings, called siphons, where water enters and leaves during feeding. Pharyngeal gill slits are present in both larvae and adults and function in both feeding and gas exchange. However, its larval stage can be as brief as a few minutes, and once a tunicate has settled on a suitable substrate, it undergoes a radical metamorphosis in which many of its chordate characters disappear. Its tail and notochord are resorbed; its nervous system degenerates; and its remaining organs rotate 90°.

How do they feed themselves?

Adult urochordates feed themselves by suspension feeding, using their pharyngeal gill slits. A mucous sheet on the inside of the pharynx traps particles present in the water that enters one siphon (incurrent siphon), passes through the pharyngeal slits into a chamber called the atrium and leaves through the other siphon (excurrent siphon). Note that the pharyngeal gill slits function in both feeding and gas exchange. Remember that larvae are a dispersal stage and do not feed.

How do they move?

Adult Tunicates are sessile, which means that they are permanently attached to its substrate. When the Tunicates are at a larval stage, they are free-swimming. Larvae swim using the notochord, which stiffens the body and functions as a simple endoskeleton to make wavelike body movements. In many species, the larva uses its tail muscles and notochord to swim through water in search of a suitable substrate on which it can settle; guided by cues it receives from light- and gravity-sensitive cells.

How do they reproduce themselves?

In most species, individuals produce both sperm and eggs. In some species, both sperm and eggs are shed into the water and fertilization is external; in other species, like sea squirts sperm are released into the water but eggs are retained, so fertilization and early development are internal. Asexual reproduction by budding is also common is some groups.

Vertebrates Chordates

The first vertebrates appeared about 470 million years ago. They were jawless marine fishes.

Although fewer than invertebrates, the group of vertebrates form a homogeneous set of animals with anatomical characteristics in common. They owe their name to the existence of a skeleton made of bone (or cartilage in some fishes) whose essential part is the spine. All have a nervous system consisting of an anterior part, the brain, lodged in the skull, and a posterior, the spinal cord, housed in a cavity (the spinal canal) formed by all the vertebrae. They also have a circulatory system formed by the heart and blood vessels (arteries and veins), in which circulates the blood that transports oxygen for breathing. NathalieR 9 janvier 2011 à 18:17 (CET)

The vertebrates are very different from the tunicates and the lancelets in different aspects:

Vertebrate column : In all vertebrates except the earliest diverging fishes, the notochord is replaced during the embryonic development by a vertebral column. The vertebral column is a series of bony or catilaginous vertebrae that enclose and protect the dorsal nerve cord like a sleeve.

The head : Vertebrates have a distinct and well-differentiated head with three pair of well-developed sensory organs; the brain is encased within a protective box, the skull, or cranium, made of bone or cartilage.

The neural crest : A unique group of embryonic cells called the neural crest contributes to the development of many vertebrates structures.

Internal organs : This characteristic of vertebrates include a liver, kidneys and and the endoctrine glands. All vertebrates have a heart and a closd circulatory system.

Endoskeleton: The endoskeleton of most vertebrates is made of cartilage or bone. cartilage and bone are specialized tissues containing fibers or protein collagen compacted together. The vertebrates endoskeleton makes possible the great size and extraordinary power of movement that characterize this group.

MelanieD 14 janvier 2011 à 12:16 (CET)

The vertebrates are the fishes , amphibians, reptiles, birds and mammals. The particularity of the vertebrate is that it has a vertebral column. So the vertebrates can be considered as segmented animals. They have a an internal skeleton too, it's a living jointed endoskeleton, with paired appendages. Vertebrates shows cephalization, their distinct head contains the brain and exhibits special sense organs, such as camera-type eyes. Vertebrates have a large coelom and well-developed viscera : the complex digestive system is complete, having both a mouth and an anus.The blood contained entirely within blood vessels, therefore, the circulatory system is said to be closed. Vertebrates have efficient means of respiration and excretion. MelanieD 17 janvier 2011 à 11:20 (CET)

Vertebrates are animals who are closest to the man (who is also a vertebrate). Moreover, they are almost all the useful species to man. They live in all environments, in water or on land.{

The first vertebrates were fishes, which some species have become amphibians. The reptiles were formed from these amphibians. Birds and mammals come from reptiles.NathalieR 9 janvier 2011 à 18:21 (CET)

Classification of the vertebrates

Vertebrates are divided into 5 main groups, or classes, each characterized by a particular lifestyle and a special anatomy.

• First appeared the fishes, during the Paleozoic era, 470 million years ago. They are aquatic animals that breathe through gills; they have no legs but fins, and their bodies are usually covered with scales. These are the most numerous and most diverse of the vertebrates: there are about 30,000 species.
• Amphibians (frogs, newts, salamanders) were formed from fishes that, 360 million years ago, began to leave the water and move onto land. These are the first vertebrates to have 4 legs; the young have gills, adults, lungs. Unlike fish, their skin is naked, that is to say, without scales. There are only 3000 species that are mainly found in wetlands.

• The reptiles were born at the end of the Paleozoic era, 290 million years ago. Most have 4 legs, but arranged in such a way that they badly support the body. That is why they move by crawling. This mode of travel is even more pronounced in snakes, which are legless reptiles. The reptiles were numerous and varied in the Mesozoic era, the so-called because of this "Age of Reptiles"(or "age of dinosaurs", which are typical reptiles at the time). It remains today only a small number of them, including turtles, crocodiles, lizards and snakes.

• Birds appeared 150 million years ago. The first "bird" known, the Archaeopteryx, is actually a kind of feathered dinosaur: he possessed both reptilian characters (teeth and a long tail) and characters of bird (feathers). Nowadays, there are about 8000 species of birds that inhabit all environments, including those coldest as the Antarctic continent.

However, birds are now considered as fully-fledged reptiles and thus appear in the reptilia class.

• Mammals appeared roughly at the same time as dinosaurs, during the Mesozoic era, 200 million years ago, from very odd reptiles called "mammalian reptiles". However, they have only become numerous and varied at the Cenozoic era, about 65 million years ago, when most of the reptiles had disappeared. It is for this reason that the Cenozoic era has been called "age of mammals".Mammals are identified by their bodies covered with hair and the existence of breasts producing milk used to feed the young. Unlike other vertebrates that lay eggs (called oviparous), mammals (except the platypus) are viviparous: they give birth to fully formed young.NathalieR 9 janvier 2011 à 19:44 (CET)

*see Appendix Chordates 2
This phylogenetic hypothesis shows the major clades of chordates in relation to the other main deuterostome clade, Echinodermata.

Fishes

The first vertebrates werejawless fishes, which wiggled through the water and sucked up foodfrom the ocean floor.

Today there are three classes of fishes  :

Jawless fishes

They have smooth,scaleless skin and no jaws or paired fins. The two groups of living jawless fishes are hagfishes and lampreys. They feed mainly dead fishes. The lamprey attaches itself to another fish and taps into its circulatory system.

Cartilaginous Fishes

The rays, the skates and the sharks belong to the cartilaginous fishes. These fishes have have skeletons of cartilage, instead bone. The largest sharks, the whale sharks, feed on small fishes and marine invertebrates and do not attack humans.

Three well-developed senses enable sharks to detect their prey:

1. They can sense some electric currents in water,ven those generated by the muscle movement of animals.
2. They have a lateral line system, it allow them to sense the pressure waves caused by a fish or another animal swimming nearby.
3. They have a keen sense of smell

The shark

'How do they breathe?To breathes, the water must enter through the mouth and out through the gills, where oxygen is taken.

How do they reproduce themselves? They reproduce in the oceans. After the fecundation, the development of the embryo can be different, according the species it can be : oviparous: laying eggs viviparous: development in the womb with a placenta ovoviviparous: the eggs develop and hatch inside the abdomen of the same mother, but it is not linked to unborn babies, they are completely independent.

What do they eat? They are at the end of the marine food chain, their feeding is very diverse: Mollusks, crustaceans, echinoderms, fish, turtles, birds, mammals.

Bony fishes

The bony fishes are the most numerous and diverse of all vertebrates. The most common bony fishes that we eat are ray-finned fishes.

Their fins, which are used to balance and propel the body, are thin and supported by bony spikes. Ray-finned fishes have various ways of life. Some, such as hering are filter feeders and other such as piranhas and barracudas are predaceous carnivores. The ray-finned fishes have a swim bladder, which usually serves as a buoyancy organs. The streamlined shape, fins and muscle action of ray-finned fishes are all suited to locomotion the water. Their skin is covered by bony scales that protect the body but do not prevent water loss. When fishes respire, the gills are kept continuously moist by the passage of the water through the mouth and out the gill slits.

MelanieD 31 janvier 2011 à 11:26 (CET)

Amphibians

Amphibians (class Amphibia), whose class name means living on both land and in the water, are represented today by frogs, toads, newts, and salamanders. Aside from jointed limbs, amphibians have other features not seen in bony fishes: eyelids for keeping their eyes moist, ears adapted to picking up sound waves, and avoice-producing larynx. Adults usually have small lungs and their hearth has only three chambers, compared to the four of mammals.

Most members of this group lead an amphibious life - that is, the larval stage lives in the water, and the adult stage lives on the land. However, the adult usually returns to the water to reproduce.

In a frog, the head and trunk are fused, and the long hind-limbs are specialized for jumping. Frogs have smooth skin, and they live in or near fresh water; toads have stout bodies and warty skin, and they live in dark, damp places away from the water. Most salamanders have limbs that are set at right angles to the body and resemble the earliest fossil amphibians. they move like a fish, with a side-to-side, S-shaped motion.NathalieR 7 février 2011 à 10:38 (CET)

The frogs

Where do they live ? The frogs can live on land and in fresh water,but they can't survive in salt water.

What do they eat? The frog is a carnivore, it eats invertebrates like insects, spiders, millipede, snails, crayfishes. The tadpoles, they feed on aquatic plants.

How do they reproduce themselves? This amphibian is oviparous, it lays eggs. It lays approximately between 2000 and 5000 eggs. There are three development stages: egg, tadpole, the adult.

How do they breathe ? They have a respiration through the skin.The skin exchanges oxygen (O2) and carbon dioxide (CO2) directly. They have a pulmonary respiration too.This respiration happens in the lungs where there is exchange of O2 and CO2.

MelanieD 13 février 2011 à 14:08 (CET)

Reptiles

Reptiles (class Reptilia) diversified and were most abundant between 245 and 66 MYA. These animals included themammal-like reptiles, the ancestors of today's living mammals, and dinosaurs, which became extinct, except for those that evolved into birds.

The reptiles living today are mainly alligators, crocodiles, turtles, snakes, lizards, and tuataras. The body of a reptile is covered with, keratinized scales, which protect the animal from desiccation and from predators. Reptiles have well-developed lungs enclosed by a protective rib cage and their heart has four chambers.

Perhaps the most outstanding adaptation of the reptiles is their means of reproduction, which is suitable to a land existence. Fertilization is internal, and the female lays leathery, flexible, shelled eggs. The amniotic egg made development on land possible and eliminated the need for a swimming larval stage during development.

Fishes, amphibians, and reptiles are ectotherms, meaning that their body temperature matches the temperature of the external environment. Reptiles regulate their body temperatures by exposing themselves to the sun if they need warmth or by hiding in the shadows if they need cooling off.NathalieR 7 février 2011 à 10:57 (CET)

One of the characterisctics of the birds is the presence offeathers which are modified reptilian scales. Birds lay ahard-shelled amniotic egg, rather than the leathery egg of reptiles. Ample data today indicate that birds are closely related to bipedal dinosaurs and they should be classified as such. Nearly every anatomic feature of a bird can be related to its ability to fly. The forelimbs are modified as wings. To fly they need an airstream and a powerful wing downstroke for lift, a force at right angles to the airstream. Thehollow , very light bones are laced with air cavities. A horny beak has replaced jaws equipped with teeth. Respiration is efficient, since the lobular lungs form anterior and posterior air sacs. The presence of these sacs means that the air moves one way through the lungs, and gases are continuously exchanged across respiratory tissues. Birds are endotherms and generateinternal beat. Many endotherms can use metabolic heat to maintain a constant internal temperature. Birds have particularly acute vision and well-developed brains. Their muscle reflexes are excellent. These adaptations are suited to flight. Another aspect of bird behavior is the seasonal migration of many species over very long distances.

The classification of birds was particularly based on type of beak and foot, and to some extend on habitat and behavior.

The snake

How do they reproduce themselves?

All snakes employ an internal fertilization. Most species of snakes lay eggs but most snakes abandon the eggs shortly after laying.

Where do they live? They can live in an terrestrial environment or in a aquatic environment.

What do they feed? The snakes eat other animals, but to kill them some snakes who are venomous uses the poison in their teeth to help them bite and capture an animal at once. They feed on birds, fish, eggs, lizards, or even other snakes

MelanieD 7 février 2011 à 10:57 (CET)

Mammals

There are two major lineages of amniotes: one that led to thereptiles and one that produced the mammals. It's approximately 200milion years ago (during the Mesozoic era) that the first mammalsappears,.The first mammals were small, about the size of mice, theywere in fact nocturnal insect-eaters. After the downfall of thedinosaurs the became much more diverse.

The two chief characteristics of mammals

Hair : Mammals are endotherms, and many of their adaptations are related to temperature control. Hair, for example, provides insulation against heat loss and allows them to be active, even in cold weather.
Milk-producing mammary glands:Mammary glands enable females to feed (nurse) their young without leaving them to find food. In most mammals, the young are born alive after a period of development in the uterus, a part of the female reproductive system.

There are three major groups of mammals : the monotremes, themarsupials and the eutherians. The duck-pilled platypus and theechidna are the only existing species of monotremes, egg-layingmammals. Most mammals are born rather than ratched. During inmarsupials and eutherians, the embryos are nurturedinside the mother by an organ called the placenta (We will talk aboutthat after). Marsupials are pouched mammals whoincluded kangaroos, koalas and opossums. These mammals have a briefgestation and give birth to tiny empryonic offspring that complete.development while attached to the mother's nipples. Eutheriansare also called placenta mammals. Eutherians make up almost 95 %of the 4 500 species of living mammals. Dogs, cats, cows,rodents, rabbits are all examples of eutherian mammals. One of theeutherian groups is the primate , which includes monkeys, apes and ofcourse the humans.

The vast majority of livingmammals are placental mammals. In these mammals, the extraembryonic membranes of the reptilian egg have been modified for internal development within the uterus of the female. Here, nutrients, oxygen, and wastes are exchanged between fetal and maternal blood. Mammals are adapted to life on land and have limbs that allow them to move rapidly. Their brain is well developed; the lungs are expanded not only by the action of the rib cage but also by the contraction of the diaphragm, a horizontal muscle that divides the thoracic cavity from the abdominal cavity; and their heart has four chambers. The internal temperature is constant, and hair, when abundant, helps insulate the body.

The mammalian brain is enlarged due to the expansion of the cerebral hemispheres that control the rest of the brain. The brain is not fully developed until after birth, and young learn to take care of themselves during a period of dependency on their parents.Placental mammals can be distinguished by their mode of locomotion and their way of obtaining food. The specific shape and size of the teeth may be associated with whether the mammal is an herbivore, a carnivore, or an omnivore.

The tiger

Where do they live ?

A tiger's habitat is dependant on two basic factors. Firstly, it should provide good cover for stalking and secondly, it should have a good abundance of prey.

What do they eat?

A tiger's favorite prey is deer and wild boar. Depending on the habitat, tigers may also eat antelope, buffalo, guar, domestic livestock, peafowl, monkeys, civets, porcupines, fish, frogs, crabs, large monitor lizards, pythons, and young elephants or rhinos. Grass, fruits, and berries are also eaten.

How do they reproduce themselves?

The mating season is mostly from around November to April, in tropical climates, and during the winter months in temperate regions. After a gestation of 100 to 112 days, 2 to 3 cubs are born. The cubs are blind and helpless and have about 1 kg each. A tiger cub can gain 100 grams in weight per day. Unfortunately one cub frequently dies at birth. The tiger cub will make its first kill around 18 months of age and will leave its mother at about 2.5 years.

How do they breathe ?

Tigers breath the same way that all cats and you and I breath. Their chest muscles pump their lungs in and out which makes air go in and out.

Utilisateur:MelanieD MelanieD 23 février 2011 é 21:10 (CET)

NathalieR 7 février 2011 à 11:30 (CET)

References

• Wikipédia
• L'Aventure de la vie, Larousse
• Concepts of Biology, Sylvia S. Mader
• http://en.wikipedia.org/wiki/Snake ...
• http://en.wikipedia.org/wiki/Frog ...

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