Tissue Development: Phylum Cnidaria

Cnidarians (from the Greek knide meaning nettle) re play the next higher score of organization of animals. They be radially symmetric and possess current tissues. However, like sponges, cnidarians arrive only two germ layers: ectoderm and endoderm. A middle layer, called mesoglea, is largely composed of a gelatinlike material. Hydra, jellyfish, sea anem whizs, and coral colonies belong to this diverse group. Members of this phylum, which consists of about 10 000 species, are arrange exclusively in aquatic ecosystems. The cheery majority reside in marine environments and are gross along Canadas three shorelines. Fewer than 50 species potful be found in freshwater ecosystems, hydra being genius of the most commonly occurring cnidarians in our lakes and ponds. The evolutionary advances that the cnidarians demonstrate compared with the diminutive complex sponges can be attributed to the development of true tissues. Cnidarians present specialized nerve, muscle, and diges tive tissues. A nerve net encircles their body. nearly of the free-swimming forms have a ring of nerve cells much or less the bell, perhaps the primitive beginning of a central loathsome system. If hydra or sea anemones are touched, they respond by flattening out and pulling their tentacles inward. This type of transaction indicates coordination of nerves and muscles, something non seen in the primitive sponge. Cnidarians capture food by development specialized cells called cnidocytes, which arrest sacs known as nematocysts.

The nematocysts contain coiled, hollow, filamentlike tubes that can shoot out rapidly and put over the shi nny of a prey or predator, some injecting to! xic material. If sufficient nematocysts are triggered, the target can be paralyzed. Thousands of nematocysts can be found on a single tentacle. Beach-goers may have painful memories of toxin-laden nematocysts. Thousands of the stinging cells can be found along the tentacles of jellyfish and floating bell-shaped colonies. The purple-colored medusa, or Vellela, from time to time floats... If you exigency to get a full essay, order it on our website: BestEssayCheap.com

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