Topic: Basis of Classification

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Top­ic: Basis of Clas­si­fi­ca­tion

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Need for Clas­si­fi­ca­tion:

• • There are over a mil­lion species of ani­mals described, mak­ing clas­si­fi­ca­tion cru­cial.
  • Clas­si­fi­ca­tion helps in orga­niz­ing ani­mals based on their sim­i­lar­i­ties and dif­fer­ences.
  • It also helps in assign­ing a sys­tem­at­ic posi­tion to new­ly dis­cov­ered species.
• Com­mon Fea­tures Across Ani­mal Species: Despite dif­fer­ences in struc­ture and form, ani­mals share fun­da­men­tal fea­tures, which form the basis of clas­si­fi­ca­tion.
• Key Fea­tures Used for Clas­si­fi­ca­tion:
• Arrange­ment of Cells: Ani­mals show vari­a­tion in the arrange­ment of cells in tis­sues and organs.   Cel­lu­lar struc­ture and orga­ni­za­tion, such as the pres­ence of tis­sues, organs, and sys­tems, are essen­tial in clas­si­fi­ca­tion.
• Body Sym­me­try: Sym­me­try refers to the bal­anced arrange­ment of body parts.           

Types of body sym­me­try include:             
Radi­al Sym­me­try                                           Bilat­er­al Sym­me­try                                   Asym­me­try

• Germ Lay­ers: Dur­ing embryo for­ma­tion, three ger­mi­nal lay­ers are formed — Ecto­derm, Meso­derm, Endo­derm. Depend­ing on the no. of these ger­mi­nal lay­ers ani­mals are of two types:     * Diploblas­tic                                                                *Triploblas­tic 

Nature of Coelom: Coelom is the body cav­i­ty between the diges­tive tract and body wall.  Based on the coelom, ani­mals can be clas­si­fied as:                                                           
Coelo­mates: Have a true coelom (e.g., ver­te­brates).                                 

Pseudo­coelo­mates: Have a false coelom (e.g., round­worms).                                        Acoelo­mates: Lack a coelom (e.g., flat­worms).

Pat­terns of Diges­tive, Cir­cu­la­to­ry, and Repro­duc­tive Sys­tems:                                 Ani­mals exhib­it dif­fer­ent pat­terns in their diges­tive, cir­cu­la­to­ry, and repro­duc­tive sys­tems.   *These sys­tems can be clas­si­fied based on:

• • Diges­tive Sys­tem: Com­plete (with mouth and anus) or incom­plete (with one open­ing for both intake and ejec­tion).
  • Cir­cu­la­to­ry Sys­tem: Open or closed cir­cu­la­to­ry sys­tem.
  • Repro­duc­tive Sys­tem: Sex­u­al (with sep­a­rate sex­es or her­maph­ro­dit­ic) or asex­u­al repro­duc­tion.           
  • Seg­men­ta­tion: Repet­i­tive divi­sion of body parts into seg­ments.
  • Noto­chord: dur­ing embry­on­ic devel­op­ment a flex­i­ble rod like struc­ture is formed which is known as Noto­chord.

        Clas­si­fi­ca­tion is based on the com­par­i­son of   fun­da­men­tal fea­tures like body sym­me­try, coelom, and organ sys­tems. 

These shared char­ac­ter­is­tics help in group­ing ani­mals sys­tem­at­i­cal­ly, allow­ing bet­ter under­stand­ing and iden­ti­fi­ca­tion of new species.