Table of Contents
Affinities of Herdmania with Non-chordate:
- Like porifera and coelenterata Urochordata are sessile live in marine environment.
- Larval eyes and otocysts present in Urochordata show great similarity with some invertebrates.
- In Herdmania intestine have typhlosole which also present in some other invertebrates.
- Herdmania sometimes live in colonial form which shows great resemblance with some other invertebrates.
- Food collection and respiratory gases comes through the water current in Herdmania similar with some other invertebrates like sponges.
But those similarities do not indicate that Urochordata is in the same line of evolution as that of other Non-chordate, the similarities present may be due to living in similar environmental conditions.
Affinities of Herdmania with Chordata:
In the larval stage Herdmania shows great resemblance with Chordata, in their larval stage, all the fundamental Chordata characters are present, rod-shaped notochord form axial skeleton in the tail, gill slits in the pharyngeal wall, dorsal tubular nerve cord.
Affinities of Herdmania with Hemichordata:
- Herdmania and Hemichordata show great similarity in structure of pharynx and gill slits and other structures related to pharynx.
- Development of central nervous system in Herdmania and other Hemichordata show much similarity.
- Notochord is restricted in Herdmania as well as in Hemichordata.
Objections:
- Hemichordata like Balanoglossus generally live in burrows but Herdmania generally live pelagic life at the ocean floor.
- In Hemichordata body divided into three parts, proboscis, collar and trunk but in Herdmania body do not show such differentiation.
- In Ascidian larva the tail region have true notochord but in Hemichordata the notochord like structure is not actually notochord, it is buccal diverticulum.
Affinities of Cephaochordata with Herdmania:
- Ciliary feeding mechanism and respiration mechanism is more or less similar in Cephaochordata and Herdmania.
- Branchial tentacle present inside the branchial siphon is similar with velar tentacle.
- Endostyle structure present in Herdmania show great similarity with Cephaochordata.
- Structure of pharynx and associated structure is similar in Herdmania and Chephalochordata.
- Atrial aperture and atrial siphon present in Herdmania have resemblance with Cephaochordata.
- In early stages of embryonic development Herdmania and Cephaochordata show great resemblance.
- Ascidian larva have tail with mid vertical fin also present in Hemichordata.
- Both Ascidian and Cephaochordata show some common sense organs, otocyst, ocellus.
Objections:
- In adult stage Ascidian are pelagic but in adult stage Cephaochordata are free swimming.
- True coelom present in Cephaochordatachordata but there are no coelom in Ascidian.
- In Herdmania heart present but in Chephalochordata heart absent.
- Herdmania is hermaphrodite, both male and female reproductive system present in a single individual but Cephaochordata are unisexual.
- In Herdmania metamorphosis is retrogressive in nature but in Cephaochordata it is progressive.
- In Ascidian a special protective covering test present but in Chephalochordata there are no such structure.
- In Herdmania notochord present in their tadpole larva but it absent in adult stage while in Cephaochordata notochord present in adult stage.
Affinities of Herdmania with Vertebrata:
- Dorsal nervecord present in vertebrate also present in tadpole larva of Ascidian.
- Axial skeleton in vertebrate is similar to notochord in Herdmania.
- Perforated pharyngeal wall due to presence of gill slits is observed in both Herdmania and Vertebrata.
- Neural gland in Herdmania is mainly excretory organ but it is homologous to the pituitary gland in vertebrate.
- Endostyle in Herdmania show great resemblance with thyroid gland in vertebrate.
Systematic Position of Herdmania:
The systematic position of Herdmania, Urochordata is controversial due to their affinities with multiple groups of animals. Different workers tried to place Herdmania with different animal groups, Cuvier placed Herdmania along with Mollusca, Lamarck placed them between Radiata and Vermes, Milne tried to place Herdmania and Bryozoa together, Huxley placed Herdmania along with Brachiopoda. But Kowalevsky noticed a great similarity between Herdmania and Chordata, he placed Herdmania under Urochordata in phylum Chordata.
Reference Habitat and Habits of Herdmania
Detailed Information on
Habitat and Habits of Herdmania
External Morphology of Herdmania
Mantle Viscera and Coelom of Herdmania
Blood Vascular System of Herdmania
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