HEMICHORDATA : Affinities2nd Sem (C3T)

Dr. Ranajit Kr. KhaluaAssistant Professor

Dept. zoology

Narajole Raj CollegePaschim Medinipur

• Metschnikoff (1865) stated that the group Enteropneusta had certain affinities with Echinodermata.

• Spengel (1893) showed the relationship of Enteropneusta with Annelida.

• Sedgwick and Huxley (1814) suggested the affinites Enteropneusta with the vertebrates.

• Hyman (1959) assigned the position of an independent phylum to hemichordata in the invertebrata.

Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College

Affinities with Annelida• Resemblances : The main resemblances of

hemichordata with Annelida are as follows :

1. The general body form andburrowing habit of tubicolous forms are alike and mud is ingested in burrowing. It ia pasaed out from the anus as castings.

2. The vascular system of most emichordates is like that ofannelids with blood flowing anteriorly in the dorsal vessel andposteriorly in the ventral vessel

Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College

• Differences : The differences between two groups are so great that there can be no phylogenetic relationship between them. The differences are as follows :

1. Gill-slits are absent in annelida

2. Paired nerve cords are present in annelida.

Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College

❑ The larva of hemichordata an Annelida also differ in the following ways :

I. Nephridia are absent in tornaria larva.

II. Pre-oral coelom ls absent in trochosphere larva.

III. In trochosphere blastopore becomes the mouth while in tornaria it become the anus

Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College

Affinities with Echinodermata:

The only anatomical similarity between them is their nervous system which in both cases consist of a nerve lying near the surface embedded in the epidermis. There is strong affinity between the two phylaon embryological evidence.The tornaria larva shows a very striking resemblance with the auricularia larva and specially with bipinnaria of Asteroidea.

Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College

• Resemblances : the resemblances extends in to the following details :

1. The ciliated band is identical and follows the same course in the tornaria and the auricularia and bipinnaria, thought the telotroch and eye spots of the tornaria are absent in echinoderm larva.

2. In both groups the blastopore become a larval anus.

3. The cleavage and gastrulation follow the same pattern in both.

Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College

• Differences : There are following differences between two groups :

1. Eye spot ia absent in bipinnaria

2. The apical plate and telotroch are absent in bipinnaria.

3. The protocoel is paired in echinoderms, while unpaired in tornaria larva

Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College

Affinities with chordata:

Bateson (1887) included hemichordata in phylum

chordata, since then a close relationship has been

acknowledge between hemichordates and chordates

Resemblances: The Phylogenetic relationship of

hemiichordates and cohordates is based on the

supposed presence of the three fundamental chordate

characters in both groups, viz, notochord, gill-clefts

Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College

Differences: the inclusion of hemichordates in phylum Chordata cannot be justified on a few similarities which are more than the important differences. The main differences are :

1. Chordates do not have the body and coelomicregions corresponding to those of emichordates.

2. The circulatory and nervous systems of hemichordates are like those of invertebrates.

3. There is no post-anal tail in hemichordates

Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College

Differences: the inclusion of hemichordates in phylum Chordata cannot be justified on a few similarities which are more than the important differences. The main differences are :

1. Chordates do not have the body and coelomicregions corresponding to those of emichordates.

2. The circulatory and nervous systems of hemichordates are like those of invertebrates.

3. There is no post-anal tail in hemichordates

Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College

Conclusion :

Hemichordates are definitely invertebrate in their construction and morphology', they are closer to the echinoderms than to the chodates. It appears most reasonable to place them in the invertebrates as an independent phylum which has arisen from an ancestral stock that has given rise, on the one hand, to echinoderms and on the other hand to hemichordates and chordates.

Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College