write the note on the affiniteis of Balonogloses with annelids?
Answers
Answer:
Affinities # Balanoglossus with Annelida:
Similarities:
1. Vermiform body.
ADVERTISEMENTS:
2. Presence of coelom.
3. Arrangement of blood vessels.
4. Collar comparable to clitellum of Oligochaeta.
5. Resemblances between Tornaria and Trochophora larva.
ADVERTISEMENTS:
Dissimilarities:
1. Nephridia present in Trochophore but absent in Tornaria.
2. Gastrulation opposite—blastopore forms mouth in Trochophore but forms anus in Tornaria.
3. Developmental aspects differ in two.
Affinities # Balanoglossus with Phoronis:
ADVERTISEMENTS:
Similarities (very few):
1. Disposition of the coelom.
2. A ring of cilia surrounding the anus.
3. Proboscis pore comparable to water pore.
Affinities # Balanoglossus with Pogonophora:
Similarities
1. Coelom enterocoelous with similar divisions.
2. Nervous system intra-epidermal.
Dissimilarities:
1. Pogonophores lack alimentary canal.
ADVERTISEMENTS:
2. Excretory structures — nephrocytes in Balaroglossus and coelomoducts in Pogonophora.
3. Gonads in the trunk region.
4. Presence of pericardial sinus in some species.
5. Septum between meso and metasome.
Affinities # Balanoglossus with Echinodermata:
Similarities:
1. Ciliated bands twisted in Tornaria, Auricularia and Bipinnaria.
2. Position of mouth and anus.
3. Divisions of larval alimentary canal.
4. Origin and development of coelom (most convincing resemblance).
Dissimilarities:
1. Eye spots in Tornaria larva wanting in Trochopore larva.
2. Protocoel paired in echinoderms, un¬paired in Tornaria.
The two are closely related groups and might have evolved from a common ancestor.
Affinities # Balanoglossus with Chordata:
Similarities:
1. Presence of gill clefts.
2. Presence of lumen only in collar nerve cord.
3. Feeding mechanism in Ammocoete larva and some amphibian larvae.
Dissimilarities:
1. Notochord absent.
2. Nervous system solid except collar nerve cord.
Affinities # Balanoglossus with Urochordata:
Similarities:
1. Pharynx and branchial apparatus.
2. Development of central part of nervous system.
3. Feeding mechanism.
Dissimilarities:
1. The two groups differ in all other aspects.
Affinities # Balanoglossus with Cephalochordata:
Similarities:
1. Branchial apparatus.
2. Arrangement of coelomic sacs.
Dissimilarities:
1. Un-segmented muscle fibres in Balanoglossus.
2. Mode of development.
Zoologists today not only disagree with the inclusion of Balanoglossus in Chordata, but even object to the use of the term Hemichordata assigned to it, their preference being for Adelochordata, as the buccal diverticulum is not considered by many to be the notochord, some believing it to be a structure similar to the pituitary body.
However, the presence of a dorsal, tubular nerve cord and pharyngeal gill slits are two undisputed chordate characters of Blanoglossus. All efforts to assign a definite systematic position to Balanoglossus have failed. Still it can be assumed that the group Hemichordata (Adelochordata) is probably at least a greatly modified branch from the base of the chordate tree.
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