Overview

Comprehensive Description

Description of Hydra

Cnidaria is one of the few members of the Cnidaria (the type of animal that includes jellyfish and sea-anenomes) that is found in freshwater. Most Cnidaria can live as tree-like polyps, or jellyfish-like medusae, but Hydra exists only at the polyp form. It has a body that is a tube made of two layers of cells with an anterior opening. Around the opening are numerous tentacles. The tentacles possess nematocysts (also called thread cells or cnidia) that explode to discharge a thread that can inject poison into prey or can hold prey. Hydra mostly eats small animals such as Daphnia. A gelatinous layer called the mesogloea separates the two layers of cells of a Hydra. The outer layer of cells is called the epidermis or ectoderm, and generates the nematocysts. The inner layer is the endoderm or gastrodermis, and produces the enzymes which digest the Hydra's food. Many members of the Cnidaria establish symbiotic relationships with other organisms, and some species of Hydra are bright green because they have many zoochlorellae living inside the body. Hydra reproduces asexually most of the time by a process of budding, young polyps becoming detached from the parent when they are fully developed. Seasonal episodes of sexual reproduction also occur, mature polyps developing gonads on the external body wall. Fertilized eggs give rise to tiny larvae which swim, attach themselves and develop into polyps which continue to reproduce by budding. Hydras not only bud but also have remarkable powers of regeneration. Hydra gets its name from a mythical creature that lived in the swamps near to the ancient city of Lerna in Argolis. It was a terrifying monster which was the offspring of Echidna (half maiden - half serpent), and Typhon (had 100 heads). The Hydra had the body of a serpent and many heads. If any of the other heads were severed another would grow in its place (in some versions two would grow). Also the Hydra's breath was enough to kill man or beast.
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Ecology

Habitat

Depth range based on 3 specimens in 5 taxa.

Environmental ranges
  Depth range (m): 0 - 20

Graphical representation

Depth range (m): 0 - 20
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Associations

Known prey organisms

Hydra (Hydra (N=1)) preys on:
Bosmina
Chironomidae
detritus

Based on studies in:
Norway: Oppland, Ovre Heimdalsvatn Lake (Lake or pond)
UK: Yorkshire, Aire, Nidd & Wharfe Rivers (River)
New Zealand: Otago, Narrowdale catchment (River)

This list may not be complete but is based on published studies.
  • P. Larson, J. E. Brittain, L. Lein, A. Lillehammer and K. Tangen, The lake ecosystem of Ovre Heimdalsvatn, Holarctic Ecology 1:304-320, from p. 311 (1978).
  • E. Percival and H. Whitehead, 1929. A quantitative study of the fauna of some types of stream-bed. J. Ecol. 17:282-314, from p. 311 & overleaf.
  • Thompson, RM and Townsend CR. 2005. Energy availability, spatial heterogeneity and ecosystem size predict food-web structure in streams. OIKOS 108: 137-148.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
Specimen Records: 74
Specimens with Sequences: 64
Specimens with Barcodes: 63
Species: 9
Species With Barcodes: 9
Public Records: 55
Public Species: 8
Public BINs: 12
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Barcode data

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Wikipedia

Hydra (genus)

Hydra /ˈhdrə/ is a genus of small, simple, fresh-water animals that possess radial symmetry. Hydra are predatory animals belonging to the phylum Cnidaria and the class Hydrozoa.[2][3] They can be found in most unpolluted fresh-water ponds, lakes, and streams in the temperate and tropical regions and can be found by gently sweeping a collecting net through weedy areas. They are multicellular organisms which are usually a few millimetres long and are best studied with a microscope. Biologists are especially interested in Hydra due to their regenerative ability; and that they appear not to age or to die of old age.

Morphology[edit]

Schematic drawing of a discharging nematocyst

Hydra has a tubular body up to 10 mm (0.39 in) long when extended, secured by a simple adhesive foot called the basal disc. Gland cells in the basal disc secrete a sticky fluid that accounts for its adhesive properties.

At the free end of the body is a mouth opening surrounded by one to twelve thin, mobile tentacles. Each tentacle, or cnida (plural: cnidae), is clothed with highly specialised stinging cells called cnidocytes. Cnidocytes contain specialized structures called nematocysts, which look like miniature light bulbs with a coiled thread inside. At the narrow outer edge of the cnidocyte is a short trigger hair called a cnidocil. Upon contact with prey, the contents of the nematocyst are explosively discharged, firing a dart-like thread containing neurotoxins into whatever triggered the release which can paralyse the prey, especially if many hundreds of nematocysts are fired.

Hydra has two main body layers, which makes it "diploblastic". The layers are separated by mesoglea, a gel-like substance. The outer layer is the epidermis, and the inner layer is called the gastrodermis, because it lines the stomach. The cells making up these two body layers are relatively simple. Hydramacin[4] is a bactericide recently discovered in Hydra; it protects the outer layer against infection.

The nervous system of Hydra is a nerve net, which is structurally simple compared to mammalian nervous systems. Hydra does not have a recognizable brain or true muscles. Nerve nets connect sensory photoreceptors and touch-sensitive nerve cells located in the body wall and tentacles.

Respiration and excretion occur by diffusion everywhere through the epidermis.

Motion and locomotion[edit]

If Hydra are alarmed or attacked, the tentacles can be retracted to small buds, and the body column itself can be retracted to a small gelatinous sphere. Hydra generally react in the same way regardless of the direction of the stimulus, and this may be due to the simplicity of the nerve net.

Hydra showing sessile behaviour

Hydra are generally sedentary or sessile, but do occasionally move quite readily, especially when hunting. They do this by bending over and attaching themselves to the substrate with the mouth and tentacles and then release the foot, which provides the usual attachment, this process is called looping. The body then bends over and makes a new place of attachment with the foot. By this process of "looping" or "somersaulting", a Hydra can move several inches (c. 100 mm) in a day. Hydra may also move by amoeboid motion of their bases or by simply detaching from the substrate and floating away in the current.

Reproduction and life cycle[edit]

When food is plentiful, many Hydra reproduce asexually by producing buds in the body wall, which grow to be miniature adults and simply break away when they are mature. When a hydra is well fed, a new bud can form every two days.[5] When conditions are harsh, often before winter or in poor feeding conditions, sexual reproduction occurs in some Hydra. Swellings in the body wall develop into either a simple ovary or testes. The testes release free-swimming gametes into the water, and these can fertilize the egg in the ovary of another individual. The fertilized eggs secrete a tough outer coating, and, as the adult dies, these resting eggs fall to the bottom of the lake or pond to await better conditions, whereupon they hatch into nymph Hydra. Some, like Hydra circumcincta and Hydra viridissima, are hermaphrodites[6] and may produce both testes and an ovary at the same time.

Many members of the Hydrozoa go through a body change from a polyp to an adult form called a medusa. However, all Hydra, despite being hydrozoans, remain as polyps throughout their lives.

Feeding[edit]

Hydra mainly feed on small aquatic invertebrates such as Daphnia and Cyclops.

When feeding, Hydra extend their body to maximum length and then slowly extend their tentacles. Despite their simple construction, the tentacles of Hydra are extraordinarily extensible and can be four to five times the length of the body. Once fully extended, the tentacles are slowly manoeuvred around waiting for contact with a suitable prey animal. Upon contact, nematocysts on the tentacle fire into the prey, and the tentacle itself coils around the prey. Within 30 seconds, most of the remaining tentacles will have already joined in the attack to subdue the struggling prey. Within two minutes, the tentacles will have surrounded the prey and moved it into the opened mouth aperture. Within ten minutes, the prey will have been enclosed within the body cavity, and digestion will have started. Hydra is able to stretch its body wall considerably in order to digest prey more than twice its size. After two or three days, the indigestible remains of the prey will be discharged by contractions through the mouth aperture.

The feeding behaviour of Hydra demonstrates the sophistication of what appears to be a simple nervous system.

Some species of Hydra exist in a mutual relationship with various types of unicellular algae. The algae are protected from predators by Hydra and, in return, photosynthetic products from the algae are beneficial as a food source to Hydra.

Morphallaxis[edit]

Main article: Morphallaxis

Hydra undergoes morphallaxis (tissue regeneration) when injured or severed.

Non-senescence[edit]

Daniel Martinez claimed in a 1998 article in Experimental Gerontology that Hydra are biologically immortal.[7] This publication has been widely cited as evidence that Hydra do not senesce (do not age), and that they are proof of the existence of non-senescing organisms generally. In 2010 Preston Estep published (also in Experimental Gerontology) a letter to the editor arguing that the Martinez data support rather than refute the hypothesis that Hydra senesce.[8]

The controversial unlimited life span of Hydra has attracted the attention of natural scientists for a long time. Research today appears to confirm Martinez' study.[9] Hydra stem cells have a capacity for indefinite self-renewal. The transcription factor, "forkhead box O" (FoxO) has been identified as a critical driver of the continuous self-renewal of Hydra.[9] A drastically reduced population growth resulted from FoxO down-regulation, so research findings do contribute to both a confirmation and an understanding of Hydra immortality.[9]

While Hydra immortality is well-supported today, the implications for human aging are still controversial. There is much optimism;[9] however, it appears that researchers still have a long way to go before they are able to understand how the results of their work might apply to the reduction or elimination of human senescence.[10]

Genomics[edit]

A draft of the genome of Hydra magnipapillata was reported in 2010.[11]

Aquarium Control[edit]

In the aquarist hobby; concentrations of .6ppm Fenbendazole has been known to kill Hydra infestations with great results and no negligible impact on other aquatic creatures. http://www.planetinverts.com/killing_planaria_and_hydra.html

See also[edit]

References[edit]

  1. ^ a b Schuchert, P. (2011). "Hydra Linnaeus, 1758". In P. Schuchert. World Hydrozoa database. World Register of Marine Species. Retrieved 2011-12-20. 
  2. ^ Gilberson, Lance (1999) Zoology Lab Manual, 4th edition. Primis Custom Publishing.
  3. ^ Solomon, E., Berg, l., Martin, D. (2002) Biology 6th edition. Brooks/Cole Publishing.
  4. ^ Jung, S. et al; Dingley, A. J.; Augustin, R.; Anton-Erxleben, F.; Stanisakin, M.; Gelhaus, C.; Gutsmann, T.; Hammer, M. U.; Podschun, R.; Bonv, A. M. J. J.; Leippe, M.; Bosch, T. C. G.; Grotzinger, J. (2009). "Hydramacin-1, structure and antibacterial activity of a protein from the basal metazoan Hydra". The Journal of Biological Chemistry 284 (3): 1896–1905. doi:10.1074/jbc.M804713200. PMID 19019828. 
  5. ^ Patton, Wendell K. "Hydra (coelenterate)." Grolier Multimedia Encyclopedia. Grolier Online, 2014. Web. 12 Aug. 2014.
  6. ^ Holstein, T. (1995) Cnidaria: Hydrozoa Süsswasserfauna von Mitteleuropa. 1/2+ 3. Stuttgart, Jena, NY: Gustav Fisher Verlag.
  7. ^ Martinez, D. E. (May 1998). "Mortality patterns suggest lack of senescence in Hydra". Experimental Gerontology 33 (3): 217–225. doi:10.1016/S0531-5565(97)00113-7. PMID 9615920. 
  8. ^ Estep, P. W. (September 2010). "Declining asexual reproduction is suggestive of senescence in Hydra: comment on Martinez, D., "Mortality patterns suggest lack of senescence in Hydra."". Experimental Gerontology 45 (3): 645–6. doi:10.1016/j.exger.2010.03.017. PMID 20398746. 
  9. ^ a b c d Boehm, Khalturin, Anton-Erxleben, Hemmrich, Klostermeier, Lopez-Quintero, Oberg, Puchert, Rosenstiel, Wittlieb, Bosch; Khalturin; Anton-Erxleben; Hemmrich; Klostermeier; Lopez-Quintero; Oberg; Puchert; Rosenstiel; Wittlieb; Bosch (2012). "FoxO is a critical regulator of stem cell maintenance in immortal Hydra". Proceedings of the National Academy of Sciences 109 (48): 19697. Bibcode:2012PNAS..10919697B. doi:10.1073/pnas.1209714109. 
  10. ^ Reason (November 2012). "Investigating the Agelessness of Hydra". FightAging.org. Retrieved 2012-11-23. 
  11. ^ Chapman, Jarrod A.; Kirkness, EF; Simakov, O; Hampson, SE; Mitros, T; Weinmaier, T; Rattei, T; Balasubramanian, PG et al. (March 2010). "The dynamic genome of Hydra". Nature 464 (7288): 592–6. Bibcode:2010Natur.464..592C. doi:10.1038/nature08830. PMID 20228792. 
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