C N I D E R I A N S

Marine Life

 

Cnidarians (coming from the Greek CNIDOS= stinging needle) are incredibly diverse in form but come in two fundamental shapes, polypoid and medusoid shapes. The main characteristic feature is the presence tentacles set in a radial symmetry with their digestive system in the middle. On these tentacles are found the nematocysts (stinging cells that can be ejected at a prey if they come close enough) used to subdue and capture food by the use of a toxin, that can be sometimes even lethal to man. Cnidarians can be found as single element or in colonies (like coral)

 

There are 9000 species (400 in the Mediterranean) of cnidarians organized in four major groups: Anthozoa, which includes true corals, anemones, and sea pens; Cubozoa, the amazing box jellies with complex eyes and potent toxins; Hydrozoa, the most diverse group with siphonophores, hydroids, fire corals, and many medusae; and Scyphozoa, the true jellyfish.

 

    Anthozoa:

    Asteroides Clycularis

    Calliactis Parasitica

    Alicia Mirabilis

    Condy Lactis Aurantiaca

 

Scyphozoa (jelly Fish)

Aurelia Aurita

Rhizostoma Pulmo

 

Hydrozoa :

Velella Vellella

 


COTHYLORIZA TUBERCULATA - CASSIOPEIA - FRIED EGG JELLY FISH

   

 

Belongs to the Order Rhizostomae. Family Cepheidae. One of the most common jellyfish in the Mediterranean sea and definitely the most colorful of all. The animal can grow to 35 cm in diameter and in contrast to most jellyfishes has an ability to move on its own. It migrates vertically while various juvenile fishes are associated with it.

This species feeds on Microplankton and has separate sexes. The eggs are fertilized internally, the larvae kept in pockets and then are released in the open water where they developed into sessile polyps.

 

 
 

 

Ctenophores - Comb Jelly

Ctenophores (Greek for "comb-bearers") have eight "comb rows" of fused cilia arranged along the sides of the animal, clearly visible along the red lines in these pictures. These cilia beat synchronously and propel ctenophores through the water. Some species move with a flapping motion of their lobes or undulations of the body. Many ctenophores have two long tentacles, but some lack tentacles completely.

Ctenophores, variously known as comb jellies, sea gooseberries, sea walnuts, or Venus's girdles, are voracious predators. Unlike cnidarians, with which they share several superficial similarities, they lack stinging cells. Instead, in order to capture prey, ctenophores possess sticky cells called colloblasts. In a few species, special cilia in the mouth are used for biting gelatinous prey.

 

 

Leucothea

 

The phylogenetic position of ctenophores has been, and still is, in dispute. Ctenophores have a pair of anal pores, which have sometimes been interpreted as homologous with the anus of bilaterian animals (worms, humans, snails, fish, etc.). Furthermore, they possess a third tissue layer between the endoderm and ectoderm, another characteristic reminiscent of the Bilateria. However, molecular data has contradicted this view, although only weakly. Therefore, this is an active area of research.

 

 

Velella Velella

 

Velella is a cosmopolitan genus of free-floating hydrozoans that live on the surface of the open ocean. There is only one known species, Velella velella, in the genus. Velella velella is commonly known by the names sea raft, by-the-wind sailor, purple sail, little sail, or simply Velella.

These small cnidarians are part of a specialised ocean surface community which includes the better-known cnidarian siphonophore, the Portuguese Man o' War. Specialized predatory gastropod mollusks prey on these cnidarians. Such predators include nudibranchs (sea slugs) in the genus Glaucus and purple snails in the genus Janthina.

Like other Cnidaria, Velella velella are carnivorous. They catch their prey, generally plankton, by means of tentacles that hang down in the water and bear cnidocysts (also called nematocysts). Though the toxins in their nematocysts are effective against their prey, V. velella is harmless to humans, either because its nematocysts are unable to pierce the skin, or perhaps because humans do not react to the toxins encapsulated in their nematocysts. Nevertheless, it is wise to avoid touching one's face or eyes after handling V. velella.

 

 

Each apparent individual Velella velella is in fact a hydroid colony, and most are less than about 7 cm long. They are usually deep blue in colour, but their most obvious feature is a small stiff sail that catches the wind and propels them over the surface of the sea. Under certain wind conditions, they may be stranded by the thousand on beaches.

 

 

Like many Hydrozoa, Velella velella has a bipartite life cycle, with a sort of alternation of generations. The deep blue by-the-wind sailors that are recognized by many beach-goers are the polyp phase of the life cycle. Each "individual" with its sail is really a hydroid colony, with many polyps that feed on ocean plankton and are connected by a canal system that enables the colony to share whatever food is ingested by individual polyps. Each by-the-wind sailor is a colony of all-male or all-female polyps. The colony has several different kinds of polyps, some of which are both feeding and reproductive, called gonozooids, and others protective, called dactylozooids.

The gonozooids each produce numerous tiny jellyfish by an asexual budding process, so that each Velella colony produces thousands of tiny jellyfish (medusae), each about 1 mm high and wide, over several weeks. The tiny medusae are each provided with many zooxanthellae, single-celled endosymbiotic organisms typically also found in corals and some sea anemones, that can utilize sunlight to provide energy to the jellyfish. Curiously, although a healthy captive Velella will release many medusae under the microscope and thus must do the same in the sea, the medusae of Velella are rarely captured in the plankton and very little is known about their natural history. The medusae develop to sexual maturity within about three weeks in the laboratory and their free-spawned eggs and sperm develop into a planktonic larva called a conaria, which develops into a new floating Velella hydroid colony (Info taken from Wikipedia).

 

 
 

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