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Wednesday 8 May 2013

Affinities and Systematic Position of Balanoglossus

Affinities with non-chordates :-

(A) With Annelida :-

(a) Similarities :-


(i) In Adult Form :-


(1) Body → elongated; vermiforms; coelomate;

(2) Heart → dorsal to gut.

(3) General Sense Organ → Absent

(4) Collar → Resembles to clitellum.

(5) Blood Vessel → Similar pattern.

(ii) In Larval Form :-

  

Tornaria of Balanoglossus resembles Trochophore larva of anelids in :

(1) Body → Transparent and spindle-shaped.

(2) Habit → Free-swimming

(3) Ciliated bonds → Transverse

(4) Apical Plate → With a tuft of cilia and eye spots.

(b) Dissimilarities :-


(i) In Adult Form :-


                   Features
                 Balanoglossus
                   Annelids
Body
Unannulated
Annulated
Pharyngeal gill slits
Present
Absent
Stomochord
Present
Absent
Excretory  organ
Glomerulus
Nephridia

(ii) In Larval Form :- 


                   Features
                 Tornaria
                   Trochophore
Cleavage
Equal
Spiral
Blastula
Hollow
Solid
Coelom formation
Enterocoelic
Schizocoelic

Remark :- 


Dissimilarities are much more prominent than superficial similarities. Balanoglossus, thus, could not be grouped together with Annelids.




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