4. Kingdom Animalia - part 12 - Phylum : Chordata

 

4. Kingdom Animalia - part 12 - Phylum : Chordata


Phylum : Chordata


  • Chordates are characterised by -
  1. presence of cartilagenous notochord at least in early embryonic life
  2. presence of gill slits in the pharyngeal (neck) region
  3. presence of hollow, dorsal nerve cord running through out the length of body and 
  4. ventral heart.


  • Phylum Chordata is divided into three subphyla-
  1. Urochordata
  2. Cephalochordata and
  3. Vertebrata. 
  • Urochordata and Cephalochordata are collectively called Protochordates.


a. Subphylum : Urochordata or Tunicata :


  • e.g. Herdmania, Salpa, Doliolum.
  • These are also called as tunicates or ascidians. 
  • They are exclusively marine. Body is soft and covered by 'test' or 'tunic' which is made up of tunicine. 
  • Notochord is present only in the tail of larva, hence the name, urochordata.
  • Notochord is lost during metamorphosis.
  • Pharynx has many gill slits. 
  • Closed circulatory system is present. 
  • Development is indirect.



b. Subphylum : Cephalochordata :


  • e.g. Branchiostoma (Amphioxus or Lancelet) 
  • They are exclusively marine. 
  • These are also called as lancelet, which are small fishlike animals that rarely exceed 5 cm in length.
  • Lancelets partly live burried in soft marine sediments. 
  • Notochord extends throughout the length of body and present throughout the life. 
  • Myotomes (muscle blocks) are present. 
  • Post-anal tail is present. 
  • Closed circulatory system is present. 
  • Blood is without pigment.


c. Subphylum : Vertebrata :


  • In these chordates, notochord is replaced by cartilaginous or bony vertebral column. 
  • It is divided into two divisions - 
  1. Agnathostomata (no jaws) and 
  2. Gnathostomata (jaws present).


Comments

Post a Comment

Popular posts from this blog

2. Systematics of Living Organisms part 03 - Units of Classification

  2. Systematics of Living Organisms part 03 - Units of Classification Units of Classification : Species : Species is the  principal natural taxonomic unit , ranking below a genus and denoted by  latin binomial  (considered as the basic) unit of classification.  It is a  group of organisms  that can interbreed under natural condition to produce fertile offspring.  It was thought to be an  indivisible, stable and static unit.   However in the modern taxonomy, subdivision of species such as  sub-species, varities and populations  are seen and given more importance. Genus :  Genus is a taxonomic rank or category  larger than species  used in the biological classification of living and fossil organisms.  Genus is a  group of species   bearing close resemblance to one another in their morphological characters but they do not interbreed.  e.g.  Tiger, Leopard, Lion  all three belong to sam...
Read more

2. Systematics of Living Organisms - part 04 - Nomenclature

  2. Systematics of Living Organisms - part 04 - Nomenclature Nomenclature : The art of naming the objects is in fact, a science called  nomenclature.  All living organisms are known by a particular name. 1.Vernacular / Local names / Common names:  Widely distributed organisms have a large number of common names.  Pansy (Viola  tricolor  L.)  grown in most European and American gardens has about 50 common English names.  In a multilingual country like India, almost all useful plants have local names which differ from language to language and even from dialect to dialect.  As in Ayurveda,  mango (Mangifera  indica  L.)  is known by over 50 different names, all in the Sanskrit language. Hence the common names obviously have limited usage and for universal applications, a unique name for a particular individual is very much essential. 2. Scientific Names :  To overcome the difficulties raised by common names, scient...
Read more

2. Systematics of Living Organisms - part 05 -Salient features of Five Kingdoms

Image
  2. Systematics of Living Organisms - part 05 -Salient features of Five Kingdoms  Salient features of Five Kingdoms : 1. Kingdom Monera : It contains unicellular organisms with prokaryotic cellular organization.  Monera includes  unicellular prokaryotic organisms. These are omnipresent.  They are found in all types of environment which are not generally inhabited by other living beings.  Few are  photoautotrophs or chemoautotrophs ; but  majority are heterotrophic  in nature.  These organisms do  not have well defined nucleus . DNA exists as a simple double stranded circular single chromosome called as  nucleoid. Smaller circular molecules of DNA as extrachromosomal genetic elements called  plasmids  are often present.  Cell wall is made up of  peptidoglycan  (also called  murein ) which is a polymer of sugars and amino acids. Membrane bound organelles e.g.  mitochondria, chloroplast, endopla...
Read more