Hydra, genus of invertebrate freshwater animals of the class Hydrozoa (phylum Cnidaria). The body of such an organism consists of a thin, usually translucent tube that measures up to about 30 millimetres (1.2 inches) long but is capable of great contraction.

A single Hydra is composed of 50,000 to 100,000 cells which consist of three specific stem cell populations that will create many different cell types. These stem cells will continually renew themselves in the body column. Hydras have two significant structures on their body: the “head” and the “foot”.

Hydra contains epithelial cells as well as a multipotent interstitial cell (I-cell) that gives rise to nematocytes, nerve cells, gland cells, and germ-line cells.

Hydridae

The Hydra is found within inland freshwater systems in Europe, Asia, and the Americas. There are between 20-30 different species of Hydra. Hydras are one of the 9,000 species belonging to the phylum ‘Cnidaria’ which are simple, radially symmetrical invertebrates with tentacles.

Hydra oligactis, as in all Cnidaria, are strictly carnivorous and eat many different kinds of small metazoans, including annelids, copepods, cladocerans, and insects. Hydra capture their food by paralyzing and killing the food organism by means of nematocysts, which are discharged into the prey.

No, their stinging cells are too weak to affect humans. If you try to touch them, they quickly retract their tentacles and ball up to avoid predation from larger animals.

Hydra are small polyps from 1 to 20 mm in body length. The body is crowned by up to 10 or 12 tentacles.

In the class Anthozoa, comprising the sea anemones and corals, the individual is always a polyp; in the class Hydrozoa, however, the individual may be either a polyp or a medusa, with most species undergoing a life cycle with both a polyp stage and a medusa stage.

In organisms that exhibit both forms, such as members of the cosmopolitan genus Obelia, the polyp is the asexual stage and the medusa the sexual stage. In such organisms the polyp, by budding, gives rise to medusae, which either detach themselves and swim away or remain permanently attached to the polyp.

Asexual Reproduction Often a polyp produced by sexual reproduction initiates growth of a colony asexually by budding. Budding occurs when a portion of the parent polyp pinches off to form a new individual.

Corals, sea anemones and jellyfish belong to a group of animals called cnidarians. They have a simple body consisting of a central gut cavity surrounded by tentacles. There are two basic cnidarian body shapes: a polyp form, which is attached to a surface; and an upside-down free-floating form called a medusa.

A polyp is the form that attaches to a surface, while a medusa is the form that is free-floating; a species of cnidarian may take each form in a different phase of its life. The medusa form predominates in the classes Scyphozoa (the common, colourful, large jellyfish) and Cubozoa.

Corals get their food from algae living in their tissues or by capturing and digesting prey. Corals also eat by catching tiny floating animals called zooplankton. At night, coral polyps come out of their skeletons to feed, stretching their long, stinging tentacles to capture critters that are floating by.

Too much food will simply go to waste. It is possible to over-feed the aquarium and stimulate algal blooms and nitrate spikes. Some aquarists feed once a month, others every day. The best approach is to carefully feed small amounts once or twice a week and see how the corals respond over several weeks.

Many corals will benefit from the food that you feed the fish and invertebrates in your tank. Copepods, Amphipods, Brine Shrimp and Mysis Shrimp will also be consumed by many corals.

Most copepods are perfectly harmless. They eat phytoplankton and detritus, and they provide a food source for many fish. Some isopods or amphipods may not be so benign. You can even buy bottles of some species to seed your tank with.

Yep, it occurs. When they exhaust their food supply, they will turn on zoas. I just got done dealing with these.

Zoas and Palys are both very hardy soft coral placing them amount the easier to keep corals and making them a excellent choice as corals for beginners. These corals can come in some spectacular colors and color combinations, among the most amazing colors to be found in any soft coral.

Benefits of Pods In Your Reef: Microcrustaceans (or “pods”) in general, and copepods in particular, are an integral component of aquatic food webs. This is so in virtually every marine environment including coral reef habitats. Therefore, pods in your reef are a healthful addition to any reef aquarium.

As with other crustaceans, copepods have a larval form. For copepods, the egg hatches into a nauplius form, with a head and a tail but no true thorax or abdomen. The larva molts several times until it resembles the adult and then, after more molts, achieves adult development.

Copepods are great for consuming plant matter, decaying fish waste and nuisance algae such as diatoms. These guys also feed on algae and detritus and help to reduce Nitrates.

Algagen recommends that you add one 8oz bottle of copepods for every 2′ of tank. So a 4ft long tank should get two 8oz bottles to establish a healthy population. Having an isolated refugium really helps to maintain a stable population of pods because it offers a safe haven for these little guys to populate and grow.