An Essay on Phylum Chordata

What is chordate?

In the scheme of classification, the animals kingdom is divided first into several majore animal groupings called phyla. You will find approximately 30 pet animal phyla currently recognized. The very last major group of the animal kingdom is recognized as phylum chordata. It had been created by Balfour in 1880. The name of the phylum comes from two Greek words, the chorde means a string or cable, and ata means bearing. Thus, chordates are family pets having a wire, i. e. , notochord. The family pets belonging to all other phyla of the pet kingdom are often termed 'the non-chordates' or 'the invertebrates' given that they have no notochord or backbone in their physiology.

Diversity of chordates:

The chordates show an astonishing variety of form, physiology and habitat.

Numerical durability: The number of chordate types is not unusually large. About 49, 000 species are on record which are only 50 % of the living varieties of mollusks, and less than 1/10 those of arthropods. Both subphyla Urochordata and cephalochordate case for nearly 2, 500 types. The subphylum vertebrata includes 46, 500 kinds of these; fishes will be the most numerous with an approximately 25, 000 varieties. It really is commonly assumed that amphibian varieties quantity about 2, 500, reptiles 6, 000, parrots 9, 000 and mammals 4, 500.

Size: Despite their moderate number of varieties, the chordates make a disproportionate contribution to the biomass of the planet earth. Nearly all of them are medium to large in size. The vertebrates, specifically, are substantially large and many of them are one of the largest of living animals. The gigantic blue whale (Balaenoptera musculus) and the tiniest fish Philippine goby (Pandaka).

Ecology: The chordates aren't only the most significant animals in existence today, but ecologically they are being among the most successful in the pet kingdom. They are able to occupy most kinds of habitats and they have adapted themselves to more modes of existence than any other group, including the arthropods. They are located in the sea, in fresh normal water, in the air, and on all elements of land from the poles to the equator. Parrots and mammals have had the opportunity to penetrate frigid climate because they have a frequent body temperature, something no other pets or animals have.

Three important chordate heroes:

Dorsal hollow nerve cord

The central anxious system of the chordates exists dorsally in the torso. It is in the form of a longitudinal, hollow or tubular nerve wire lying right above the notochord and stretching lengthwise in the body. The nerve cable or neural tube comes from the dorsal ectodermal neural plate of the embryo and encloses a cavity or canal called neurocoel. A couple of no different ganglionic enlargements. The nerve wire assists for the integration and coordination of the body activities.

Notochord or chorda dorsalis

The notochord is an elongated rod-like adaptable structure extending the distance of the body. It is present immediately under the nerve wire and right above the intestinal canal. It hails from the endodermal roof structure of the embryonic archenteron. Structurally, it comprises large vacuolated notochordal skin cells including a gelatinous matrix and encircled by an exterior fibrous and an internal elastic sheath.

Pharyngeal gill slits

In all the chordates, at some stage of their life history, some matched lateral gill clefts or gill slits perforate through the pharyngeal wall membrane of the gut behind the oral cavity. These are variously termed as pharyngeal, branchial and visceral clefts or pouches. They serve generally for the passage of drinking water from the pharynx to outdoors, thus bathing the gills for respiration. This current secondarily aids in inter feeding by retaining food allergens in the pharynx.

The three common chordates individuals were probably characteristics of the ancestral chordates. They distinguish chordates from all the animals and appear their common ancestry.

Characters common to chordates and higher non-chordates:

There are a number of features in which the chordates resemble the bigger nonchordates or invertebrates.

AXIATION: Your body in both has a definite polar axis. The anterior end differentiated into a cephalic region or head that usually proceeds in locomotion. The contrary posterior end varieties a tail generally. This longitudinal axis of the body running from check out tail is known as the antero-posterior axis.

BILATERAL SYMMETRY: Due to existence of longitudinal antero-posterior axis, the body of all chordates and most higher nonchordates exhibits bilateral symmetry i. e. ; the right and kept sides of the body are the exact mirror image of each other.

COELOM: A secondary body cavity or true coelom is present between the body wall structure and the intestinal tube, which is lined on all attributes by mesoderm. However, it differs in its mode of origin in different sets of chordates and nonchordates.

TRIPLOBLASTIC CONDITIONS: Invertebrates above the amount of coelenterates and all chordates are triploblastic pets or animals. They have got three germ tiers: - ectoderm, endoderm, & mesoderm.

METAMERISM: Metamerism is a problem in which the body comprises a linear series of similar body segments, called metameres or somites. It really is found in three phyla: Annelida, Arthropoda and Chordata. In Annelid and Arthropoda, metameric segmentation is both interior as well as exterior, whereas in chordates it is less clear alternative.

ORGAN SYSTEMS: Within an organsystem, several organs work together for the same function, such as digestive function, blood flow, respiration, etc. It is shown by all chordates and all the non chordates from nemetean worms onwards. However, the vertebrates show a greater stage of development and important unity in this than even highest invertebrates.

Advancement of Chordata over other phyla:

Phylum chordate have some advantages over other phyla credited to certain people.

Living endoskeleton: with the exception of echinoderms and some others, only chordates own a living endoskeleton. It grows in size with the rest of the body so that there is no compulsion to shed it periodically to allow for growth like the non living chitinous exoskeleton of the nonbchordates phyla. Further, this living endoskeleton enables greater independence of movement and indefinite progress so that many chordates are the largest animals of pet animal world.

Efficient respiration: the gills in aquatic chordates and the lungs in terrestrial varieties form reliable organs of respiration. The tracheal system of certain arthropods is also effective but is suitable to family pets of small size only.

Efficient blood flow: the circulatory system of chordates is well developed and the blood flows freely in the respiratory organs ensuring swift exchange of gases. Additionally, the blood-vasular system forms an important medium for several other vital activities of your body.

Centralized stressed system: the invertebrate phyla show an evergrowing trend of centralization of nervous system, getting its culmination in the bigger chordates. The sensory systems talks about the great electric power of the chordates for adapting themselves most effectively to a variety of environments.

Origin and ancestry of chordate:

While a great deal is well known about modern chordates, like the lower varieties, their source remains obscure. Experts have not succeeded in determining which lower forms have given go up to them. Their early ancestors probably were soft-bodied and kept no definite fossils remains. They need to have originated prior to Cambrian period as the oldest fossils of known vertebrates have been uncovered in late Cambrian strata. Most experts consider that the chordates have originated from invertebrates. Several theories attempt to describe the foundation of chordates from nonchordate teams, however they have serious downsides and are definately not being sufficient. One theory advocates the descent of Chordata from the Echinodermata as such. The remarkable similarities between the echinoderm and hemichordate larvae are considered as good facts for common ancestry. Garstang suggested that probably free-swimming auricularian larvae of some ancestral echinoderms changed in to chordates through paedogenesis, i. e. , prolongation of larval life without considering metamorphosis and reproducing sexually. Most zoologists now favour the deuterostome type of chordate evolution, relating to that your phyla Ehinodermata, hemichordate, & chordate show common ancestry on embryological and biochemical evidences. The protochordates provide the connecting website link between early on chordate ancestors and vertebrates. The differentiation probably took place much sooner than Cambrian period. The earliest traces of vertebrates have been found in the rocks lately Cambrian and Ordovician. A no. of fishes followed in Silurian and became loaded in the Devonian. The next times show the advancement of amphibians, reptiles, parrots, & mammals.

General individuals of phylum chordates:

Aquatic, aerial, or terrestrial. All free-living with no fully parasitic forms.

Body small to large, bilaterally symmetrical and metamerically segmented.

A postanal tail usually projects beyond the anus at some stage and could or might not exactly persist in the adult.

Exoskeleton often present; well developed generally in most vertebrates.

Body wall triploblastic with three germinal levels: ectoderm, mesoderm, & endoderm.

Coelomate pets or animals having a true coelom, enterocoelic schizocoelic in origin.

A skeletal pole, the notochord, present during life routine.

A cartilaginous or bony, living & jointed endoskeleton present in nearly all members.

Pharyngeal gill slits present at some level; may or may not be efficient.

Digestive system filled with digestive glands.

Blood vascular system shut down. Heart and soul ventral with dorsal and ventral blood vessels. Hepatic portal system well toned.

Excretory system comprising proto-or meso-or meta-nephric kidneys.

Nerve cord dorsal and tubular. Anterior and usually enlarged to create brain.

Sexes independent with rare exceptions.

Comparison of chordates with nonchordates:

S. NO.

FEATURES

CHORDATA

NONCHORDATA

1.

Symmetry

Bilateral

Radial, biradial, bilateral or lacking

2.

Metamerism

True Metamerism

True or pseudo Metamerism or lacking

3.

Post-anal tail

Usually present

lacking

4.

Grade of organization

Organ-system

Protoplasmic to organ-system

5.

Germ layers

Triploblastic

Diploblastic or Triploblastic or absent

6.

Coelom

Truly Coelomate

Acoelomate, pseudocoelomate or truly coelomate

7.

Limb derivation

From several segments

From same segment

8.

Notochord

Present at some level or replaced by a backbone made of engagement ring like vertebrae

Notochord or backbone lacking

9.

Gut position

Ventral to nerve cord

Dorsal to nerve cord

10.

Pharyngeal gill-slits

Present at some level of life

Absent

11.

Anus

Differentiated and opens before the last segment

Opens on the last portion or absent

12.

Blood vascular system

Closed

Open, finished or absent

13.

Heart

Ventrally placed

Dorsal, lateral or absent

14.

Dorsal blood vessels

Blood flows posteriorly

Blood flows anteriorly

15.

Hepatic portal system

present

Absent

16.

Haemoglobin

In red corpuscles

In plasma or absent

17.

Respiration

Through gills or lungs

Through body surface, gills or tracheae

18.

Nervous system

Hollow

Solid

19.

Brain

Dorsal to pharynx in head

Above pharynx or absent

20.

Nerve cord

Single, dorsal, without ganglia

Double, ventral, usually bearing ganglia

21.

Roots of segmental nerves

Dorsal and ventral separate

Dorsal and ventral root base not separate

22.

Reproduction

Sexual reproduction predominant

Asexual duplication predominant

23.

Regeneration power

Usually poor

Usually good

24.

Body temperature

Cold or warm-blooded

Cold-blooded

Major subdivisions of phylum chordata:

Brief classification of chordate with characters:

The chordates form a big heterogeneous grouping of customers differing widely in one another in many respects. This creates problems in their organized classification. Different strategies have been proposed by lots of taxonomists every once in awhile. The one used in this is a synthesis of the most recent ones followed here for the sake ease and proper understanding

Phylum chordate can be divided into two teams; Acrania and Craniata having contrasting character types.

Group 1 ACRANIA (protochordata)

All marine, small, primitive or lower chordates. Missing a brain, a skull or cranium, vertebral column, jaws and brain. About 2000 varieties. The Acrania is divided in to three sub phyla: hemichordate, urochordata, and cephalochordate chiefly on the position of notochord.

Subphylum 1: HEMICHORDATA

Body divided into three areas: proboscis, collar and trunk. Notochord doubtful, brief, confined to proboscis and non homologous with this of chordates.

Class 1: Enteropneusta Body large and worm-like. Gill-slits numerous. Intestine direct. Acorn or tongue worms. 3 families, 15 genera and 70 varieties. Balanoglossus, saccoglossus.

Class 2: Pterobranchia Body small and compact. Gill slits one pair or nothing, intestine U-shaped. Pterobranchs includes 2 purchases, 3 genera and 20 types. Cepalodiscus, rhabdopleura.

Class 3 Planctosphaeroidea Transparent, round and specialized tornaria larva, having extensively branched ciliary rings and L-shaped alimentary canal, represents this class. Planctosphaera pelagica.

Class 4: Graptolita The fossils graptolites were abundant in Ordovician and Silurian periods and often placed as an extinct class under hemichordate. Their tubular chitinous skeleton and colonial behaviors show an affinity with Rhabdopleura. Dendrograptus.

Subphylum 2: UROCHORDATA or TUNICATA

Notochord and nerve cord only in tadpole-like larva. Adult sac-like, often sessile and encased in a protective tunic. Tunicates.

Class 1: Ascidiacea Sessile tunicates with scattered muscles in tunic. Solitary, colonial or compound. Gill-clefts numerous. Ascidians or sea squirts. 2 subclass, 3 orders, 12 households, 37 genera and 1200 species. Herdmania, Ciona, Molgula.

Class 2: Thaliacea Free-swimming or pelagic tunicates with circular muscles in tunic. Sometimes colonial. Salps or string tunicates. 3 purchases, 5 people, 9 genera and 30 types. Salpa, Doliolum, Pyrosoma.

Class 3: Larvacea of Appendicularia Tiny, translucent, free-floating. Adults maintain many larval features including tail. Only two gill-slits. 2 orders, 2 families, 5 genera and 30 types. Oikopleura.

Subphylum 3: CEPHALOCHORDATA

Notochord and nerve cable present throughout life along whole length of body.

Class leptocardii Body fish like, segmented with specific myotomes and numerous gill-slits. Free-swimming and burrowing. Lancelets. One course, one family, 2 genera and 30 varieties. Branchiostoma, Asymmetron.

Group 2 CRANIATA (Euchordata)

Aquatic or terrestrial, usually large-sized, higher chordates or vertebrates with different brain, a vertebral column, jaws and brain protected by the skull or cranium. The Craniata includes a solo subphylum, the vertebrata.

Subphylum 4: VERTEBRATA

Notochord supplemented or changed with a vertebral column or backbone composed of overlapping vertebrae. Body divisible into head, throat, trunk and tail. Usually dioecious. This subphylum is divided into two divisions:

Division 1: Agnatha

Jawless primitive seafood like vertebrates without true jaws and paired limbs.

Class 1: Ostracodermi Several extinct purchases of early primitive heavily armoured, palaeozoic, world's first vertebrates, collectively called the ostracoderms. Cephalaspis, Drepanaspis.

Class 2: Cyclostomata Body eel-shaped, without scales, jaws and lateral fins. Oral cavity round and suctorial. Gills 5-16 pairs. Parasites and scavengers. 45 species. Lampreys (Petromyzon) and hag fishes (Myxine).

Division 2: Gnathostomata

Jawed vertebrates having true jaws and combined limbs. For convenience, some taxonomists further divided gnathostomata into two superclasses. All the fishes and seafood like aquatic gnathostomes are positioned in the superclass Pisces, whereas all the four-footed terrestrial gnathostomes in the superclass Tetrapoda. Their contrasting features are the following:

Superclass 1: PISCES

Fishes or fish-like aquatic varieties with combined as well as median fins, gills and scaly skin

Class 1: Placodermi Several extinct purchases of primitive first jawed fishes of palaeozoic with bony mind shield movably articulated with trunk shield. Placoderms, Climatius, Dinichthys.

Class 2: Chondrichthyes Typically sea. Cartilaginous endoskeleton. Skin with placoid scales. Gill-slits not included in operculum. Pelvic claspers in male. Cartilaginous fishes. About 600 varieties. Scolidion (dog fish), Chimaera (rat fish)

Class 3: Osteichthyes Freshwater and sea. Endoskeleton mostly bony. pores and skin having numerous kinds of scales apart from placoid. Gill-slits protected byan operculum. Guys without claspers. 20, 000 varieties. Labeo (rohu), Protopterus (lung seafood), Hippocampus (sea equine).

Superclass 2: Tetrapoda

land vertebrates with two pairs of pentadactyle limbs, cornified skin area and lungs.

Class 1: Amphibia Larval level usually aquatic and breaths by gills. Adult typically terrestrial and respires by lungs. Skin area moist, glandular and without external scales. Heart 3-chambered. Approximately 2500 kinds. Rana (frog), Bufo (toad), Ambystoma (salamander).

Class 2: Reptilia Terrestrial tetrapods, epidermis dry, covered by ectodermal horny scales or bony plates. Center incompletely 4-chambered, Cold-blooded, respiration by lungs, 7000 types. Hemidactylus (wall lizard), Uromastix (spiny-tailed lizard), Naja (cobra), Sphenodon, Crocodilus.

Class 3: Aves Typically flying vertebrates protected with feathers. Fore limbs revised directly into wings. No tooth in beak. Heart and soul 4-chambered. Warm blooded. About 9000 kinds. Struthio (African ostrich), Columba (pigeon), Gallus (fowl).

Class 4: Mammalia Body included in hair. Skin glandular. Feminine with mammary glands which secrete dairy for suckling the young. Heart and soul 4-chambered. Warm blooded. Air respiration vertebrates. 4500 species. Echidna (spiny anteater), Macropus (kangaroo), Rattus (rat), Homo (man).

References

Internet source:

http://www. google. com

http://www. tutornext. com

http://www. chordates. com

Books referenced:

Chordate zoology by E. L. Jordan and P. S. Verma

Modern textbook of zoology, vertebrates (dog variety-2) by R. L. Kotpal

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