Behaviour

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Jelly-fish swim directly to surface, upon reaching the surface there is an immediate inversion of the bell and pulsation ceases. The medusa sink with the oral portion upward, throwing tentacles outward into the surrounding area. This has been identified as 'fishing' because the tentacles contain stinging mechanisms to catch prey as the medusa sink.

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Growth

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If a complete medusa is cut up into multiple pieces, each piece pending it has a small portion of the bell still connected will develop into a complete medusa within two to four days. The same is also noted with a segmented egg or ciliated larva; each cut up piece will in turn develop into a new larva.

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Morphology

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'The musculature of Gonionemus can be divided into two portions, radial and circular. The former is found in the manubrium, the tentacles and the lives of attachment of the gonads to the radial canals. The latter extends over the entire surface of the subumbrella and the subumbrellar side of the velum, interrupted only by the radial canals and by the nerve ring at the bell margin. The radial musculature consists of smooth fibers, while the circular fibers are cross-striated. All of the muscle fibers are basal extensions of epidermal cells. Gastrodermal muscles are rare in medusae, and do not occur in Gonionemus' (Fraser 1962)

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Morphology

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Color varies from deep brown or orange to paler shades, except the chymiferous tubes, which are always dark. The tips of the tentacle frequently are a deep pink. The females are usually darker than the males. (Murbach 1895)

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Size

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Largest Specimens: 3 cm in diameter, having 64 tentacles.

Smallest Specimens: 6 mm in diameter, having 32 tentacles.

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Gonionemus

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Gonionemus is a genus of hydrozoans that uses adhesive discs near the middle of each tentacle to attach to eelgrass, sea lettuce, or various types of algae instead of swimming. They are small (bell diameter to 25 mm) and hard to see when hanging onto swaying seaweed. Nevertheless, they are capable of swimming when necessary. The bell is transparent, revealing the four orange to yellowish-tan gonads that lie along most of the length of the four radial canals. The pale yellow manubrium has four short, frilly lips. Up to 80 tentacles line the bell margin, with about an equal number of statocysts. Copepods are a favored prey.

This marine hydrozoan is common in warmer waters. The conspicuous stage in the dimorphic lifecycle is the small medusa. The polypoid stage is present as a tiny, solitary polyp which feeds on protozoans and other small plants and animals. The polyp stage closely resembles Hydra.

The medusae are active swimmers that propel themselves upward in the water column by rhythmic pulsations of the bell. Upon reaching the surface, the bell relaxes, the tentacles become fully extended, and any small fish or crustaceans encountered as the medusae slowly drift toward the bottom are ensnared. Occasionally, the medusae use their adhesive pads to attach to seaweeds or other objects near the bottom, extend their tentacles, and wait for prey to bump into them.

The manubrium hangs down from the center of the subrellum. It bears the cross-shaped mouth and the four short oral lobes which grip the food. Digestion begins in the center of the manubrium, which communicates with the four radial canals and the ring canal. The velum is well-developed and used in swimming. Having a velum is characteristic of the hydrozoan medusae.

The gonads are four yellowish structures embedded in the surface of the epidermis beneath the radial canals. The ovaries are more granular in appearance than the testes (sexes are separate). The gametes are shed into the sea, and the zygotes develop into ciliated planular larvae which grow into minute polyps. These polyps can bud off other polyps or medusae. The tentacles of the medusae are hollow and connected to the exumbrellar surface by a tentacular bulb where cnidoblasts are formed.

Species

References

  1. ^ Peter Schuchert (2011). Schuchert P (ed.). "Gonionemus A. Agassiz, 1862". World Hydrozoa database. World Register of Marine Species. Retrieved January 20, 2012.
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Gonionemus: Brief Summary

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Gonionemus is a genus of hydrozoans that uses adhesive discs near the middle of each tentacle to attach to eelgrass, sea lettuce, or various types of algae instead of swimming. They are small (bell diameter to 25 mm) and hard to see when hanging onto swaying seaweed. Nevertheless, they are capable of swimming when necessary. The bell is transparent, revealing the four orange to yellowish-tan gonads that lie along most of the length of the four radial canals. The pale yellow manubrium has four short, frilly lips. Up to 80 tentacles line the bell margin, with about an equal number of statocysts. Copepods are a favored prey.

This marine hydrozoan is common in warmer waters. The conspicuous stage in the dimorphic lifecycle is the small medusa. The polypoid stage is present as a tiny, solitary polyp which feeds on protozoans and other small plants and animals. The polyp stage closely resembles Hydra.

The medusae are active swimmers that propel themselves upward in the water column by rhythmic pulsations of the bell. Upon reaching the surface, the bell relaxes, the tentacles become fully extended, and any small fish or crustaceans encountered as the medusae slowly drift toward the bottom are ensnared. Occasionally, the medusae use their adhesive pads to attach to seaweeds or other objects near the bottom, extend their tentacles, and wait for prey to bump into them.

The manubrium hangs down from the center of the subrellum. It bears the cross-shaped mouth and the four short oral lobes which grip the food. Digestion begins in the center of the manubrium, which communicates with the four radial canals and the ring canal. The velum is well-developed and used in swimming. Having a velum is characteristic of the hydrozoan medusae.

The gonads are four yellowish structures embedded in the surface of the epidermis beneath the radial canals. The ovaries are more granular in appearance than the testes (sexes are separate). The gametes are shed into the sea, and the zygotes develop into ciliated planular larvae which grow into minute polyps. These polyps can bud off other polyps or medusae. The tentacles of the medusae are hollow and connected to the exumbrellar surface by a tentacular bulb where cnidoblasts are formed.

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Diagnosis

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Olindiidae medusae with slight peduncle or peduncle absent; 4 simple radial canals; no centripetal canals; folded gonads on radial canals only; evenly distributed marginal tentacles all of one kind, with adhesion organs; numerous statocysts enclosed in mesoglea. Hydroid: small, solitary, conical, devoid of hydrorhiza, with conspicuous conical hypostome and a circlet of 4-6 long tentacles; medusa buds, frustules, cysts formed by intense asexual budding.
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bibliographic citation
Bouillon, J.; Gravili, C.; Pagès, F.; Gili, J.-M.; Boero, F. (2006). An introduction to Hydrozoa. Mémoires du Muséum national d'Histoire naturelle, 194. Muséum national d'Histoire naturelle: Paris, France. ISBN 2-85653-580-1. 591 + 1 cd-rom pp.
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Schuchert, Peter, P.