Hydra vs. Obelia
The main difference between Hydra and Obelia is that the Hydra consists of polyp body form during its whole life cycle, whereas Obelia consists of both medusae and polyp body form.
Key Differences
Hydra occurs only in a freshwater ecosystem; on the other side of the coin, obelia occurs in both freshwater and marine water ecosystems.
The size of the hydra is very small; on the flip side, the size of obelia is very larger than the hydra.
The size of the hydra is 30 mm; on the other hand, the size of obelia is 25cm.
There are few species of hydra that are present in the freshwater habitat; on the other hand, a wide variety of species of obelia are present in the freshwater and marine ecosystems.
Hydra remains sessile in its whole life cycle; on the other side, obelia remains in both sessile and mobile form.
Hydra is the coelenterate that has the tubular body with tentacles all around; on the other hand, obelia is the coelenterate that has an upright body with branching composing minute cups.
Hydra reproduces sexually by the formation of gametes; on the flip side, obelia reproduces sexually only in the medusa form.
Only a few hydras live in the colonial organization; on the other hand, all the obelia occur in colonial form.
Comparison Chart
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Hydra is the coelenterate that has the tubular body with the tentacles all around
Obelia is the coelenterate that has an upright body with branching stems consisting of minute cups
Habitat
Lives only in freshwater habitat
Lives in both freshwater and marine habitat
Mobility
It remains immobile throughout its life
It remains sessile and motile during its life cycle
Sexual Reproduction
It occurs by the formation of gametes
It occurs only in the medusa form
Diversity
It contains only a few species in freshwater
It contains a vast diversity of species
Body Form
Occur only in polyp form
Occur in both polyp and medusa form
Size
It has a tiny size of 30 mm long
Its size is longer than hydra that is 25 cm long
Colonial Organization
Only a few occur in colonial form
All occur in colonial form
Hydra and Obelia Definitions
Hydra
Greek Mythology The many-headed monster that was slain by Hercules.
Obelia
Any of various marine hydroids of the genus Obelia that exist chiefly as colonies of polyps growing in a branchlike form on surfaces such as piers or rocks.
Hydra
(Astronomy)A satellite of Pluto.
Obelia
(zoology) Any of various colonial marine hydroids of the genus Obelia.
Hydra
A constellation in the equatorial region of the southern sky near Cancer, Libra, and Centaurus. Also called Snake2.
Hydra
A persistent or multifaceted problem that cannot be eradicated by a single effort.
Hydra
Any of several small solitary freshwater hydrozoans of the genus Hydra and related genera, having a cylindrical body and a mouth surrounded by tentacles.
Hydra
Any of several small freshwater polyps of the genus Hydra and related genera, having a naked cylindrical body and an oral opening surrounded by tentacles.
Hydra
(fantasy) A dragon-like creature with many heads and the ability to regrow them when maimed.
Hydra
A complex, multifarious problem or situation that cannot be solved easily and rapidly.
Hydra
A serpent or monster in the lake or marsh of Lerna, in the Peloponnesus, represented as having many heads, one of which, when cut off, was immediately succeeded by two others, unless the wound was cauterized. It was slain by Hercules. Hence, a terrible monster.
Gorgons, and Hydras, and Chimeras dire.
Hydra
Hence: A multifarious evil, or an evil having many sources; not to be overcome by a single effort.
Hydra
Any small fresh-water hydroid of the genus Hydra, usually found attached to sticks, stones, etc., by a basal sucker.
Hydra
A southern constellation of great length lying southerly from Cancer, Leo, and Virgo.
Hydra
(Greek mythology) monster with nine heads; when struck off each head was replaced by two new ones;
Hydra was slain by Hercules
Hydra
A long faint constellation in the southern hemisphere near the equator stretching between Virgo and Cancer
Hydra
Trouble that cannot be overcome by a single effort because of its many aspects or its persistent and pervasive quality;
We may be facing a hydra that defies any easy solution
Hydra
Small tubular solitary freshwater hydrozoan polyp
Hydra vs. Obelia
Hydra’s body is flat and tubular with the tentacles around; on the flip side, obelia’s body is upright with branching stems consisting of minute cups. Hydra lives only in the freshwater ecosystem; on the other hand, obelia lives in both the fresh and marine water ecosystems. Only a few hydrae live in the form of colonies; on the flip side, all the obelia live in the colonial form.
Hydra are very small in size of 30 mm long; on the other side of the coin, obelia has a very larger size than hydra consisting of 25cm long. Medusa is absent in the hydra; on the other hand, medusa is present in the obelia. Hydra consists of only sessile or immobile animals, whereas the obelia consists of both sessile or mobile animals.
Sexual reproduction in hydra usually occurs by the formation of gametes; on the flip side, sexual reproduction in obelia usually occurs in the medusae form only. Hydra does not contain the vast and enormous majority of species in freshwater habitats; on the other side, obelia includes the vast and enormous majority of species in both freshwater and marine water habitats.
What is Hydra?
Hydra considers as the freshwater invertebrate that consists of the stalk-like tubular body with the ring of tentacles all around. The size of the hydra body is very small, which equals 30 mm long, and it is very much smaller. Hydra remains immotile during its whole course of the reproductive life cycle.
It only occurs in the polyp form in the life cycle in which the hydra remains sessile and cannot move in the freshwater habitat. It is the only habitat in which the hydra lives. Hydra lacks highly specialized systems, and the gaseous exchange can occur through the simple diffusion mechanism. Only a few of the hydras live in the colonial organization and all the remaining life as an individual living organism.
Hydra usually reproduces sexually by the formation of gametes and asexually by the formation of buds that grows into the entire new individual by the process of mitosis. A hydra body consists of a mouth as a small hollow opening through which the substances can enter the body of the hydra.
Approximately 6-10 tentacles usually surround the body of the hydra that helps in the capturing of food and insects as prey towards the immotile hydra. Hydra is the diploblastic animal that belongs to the class Hydrozoa having the radial type of symmetry in its body.
What is Obelia?
Obelia considers as the organism of both freshwater and marine water habitat that consist of the upright body posture with the branching stem consisting of minute cups. It is usually sedentary. The size of obelia is very larger than the size of hydra, which equals to the 25 cm long. Obelia does not remain sessile during its whole life cycle, but it also remains motile in the medusa form.
Unlike hydra, it usually occurs in two forms one is a polyp, and the second one is the medusa. It is present in both the freshwater and marine water habitat. It also has a vast and greater majority of species in both the ecosystems. It usually reproduces asexually only in the medusa form by the formation of gametes. It is usually present in the branched tree-like structure, which is known as the sea fur.
It also lacks the highly specialized body mechanisms, and the movement of substances across the body surface only occurs by the simple diffusion mechanism. The obelia is the diploblastic animal having the radial type of symmetry in its body. It usually relates to the class Hydrozoa. It usually made of a hollow structure during its whole extent.
