The upcoming discussion will update you about the difference between obelia and aurelia.
Difference # Obelia:
A. Medusa:
1. It has a small size, often called swimming bell and the medusa is produced by budding from blastostyles of polypoid obelia colony.
2. Medusa phase is reduced.
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3. The bell margin is entire and is provided with few long, solid tentacles.
4. The velum contains an endodermal ring canal. Craspedote medusa.
5. Oral arms absent and the manubrium is comparatively elongated.
6. Gastric ridges and gastric filaments are absent.
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7. Muscle strands are derived from both epidermis and gastro dermis.
8. Ocelli and olfactory pits are absent.
9. Statocysts are ectodermal and unprotected by hood and marginal lappets.
10.Gonads lie on radial canals externally and the gametes are ectodermal.
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11.The sub genital pit is absent.
B. Polyp:
12. Obelia colony or polypoid stage is the dominant phase; the adult form is trimorphic.
13. Hydrocaulus and hydrorhiza separable into perisarc and coenosarc.
14. Life history is remarkable for metagenesis.
C. Development:
15. Fertilization is external, occurring in water.
16. The cleavage is holoblastic and equal.
17. Planula larva is without a blastopore and coelenteron.
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18. Planula finally grows into a simple hydrula stage which by repeated budding, produces obelia colony.
Difference # Aurelia:
1. The size is large, often called jelly fish, and is formed by metamorphosis of ephyra, which is produced by strobilation of scyphistoma.
2. Medusa phase is dominant.
3. The bell margin is notched at eight radii having tentaculocysts and beset with many small tentacles.
4. Velum is absent but the velarium containing endodermal canal is present. Acraspedote medusa.
5. Four long oral arms, one at each corner of the four-sided mouth. The manubrium is comparatively short.
6. Gastric ridges bearing endodermal gastric filaments are pre-sent.
7. Muscle strands are derived only from the epidermis.
8. Ocelli and olfactory pits are present.
9. Tentaculocysts are endodermal and protected by hood and marginal lappets.
10. Gonads lie on the floor of gastric pouches internally and the gametes are endodermal.
11. The sub-genital pit is present.
12. The scyphistoma or polypoid stage is very much -reduced. It is solitary and a larval stage.
13. No such structure.
14. No true metagenesis but a case of metamorphosis complicated by multiplication in the larval stage.
15. Fertilization internal, the union occurs inside the enteron of the female.
16. Cleavage holoblastic but unequal.
17. Planula possesses a blastopore and a coelenteron.
18. The planula is transformed into a hydra tuba, which produces new hydra tuba by budding. The hydra tuba grows into a trumpet-like asexual polypoid scyphistoma which by strobilation or metamorphosis produces the Aurelia medusa.