07-05-2012, 05:24 PM
Phylum Porifera
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Phylum Porifera (Sponges)
Simple multicellular animals that spend their lives anchored to a rock or ocean bottom; they are mostly marine but some species live in fresh water; sponges have radial symmetry with a cylindrical, globose or irregular body containing an internal skeleton of minute spicules made of calcium carbonate, silica, or a fibrous collagen protein called spongin; the surface contains numerous pores connecting to canals and chambers lined by flagellated collar cells (choanocytes); sponges are filter-feeders, taking in microscopic plankton by miniature currents created by the choanocytes; sponges are divided into three classes: Class Calcarea (chalk sponges) with calcareous spicules; Class Hexactinellida (glass sponges) with siliceous spicules; and Class Demospongiae (horn sponges) with a skeleton of spongin or none; calcareous and siliceous sponge spicules often become components of tropical beach sand.
Phylum Coelenterata (Cnidaria) Corals & Jellyfish Marine and freshwater animals with radial symmetry; this phylum has two distinct body forms: a solitary or colonial polyp and a bell-shaped, free swimming medusa; both polyps and medusae are often fringed with stinging tentacles; the tentacles bear rows of "stinging cells" or cnidoblasts, each containing a "stinging organelle" known as a nematocyst; some coelenterates (Obelia) have both polyp and medusa stages in their diplontic life cycle; coelenterates are divided into three classes: Class Hydrozoa (hydroids), including the freshwater Hydra, Obelia and colonial Physalia (Portuguese man-of-war) with stinging tentacles and a bladderlike air float; Class Scyphozoa (jellyfishes); and Class Anthozoa (sea anemones and corals); in true corals, the individual tentacle-bearing polyp lives inside a calcareous chamber that it secretes; extensive, contiguous colonies of coral polyps form massive calcareous reefs in shallow tropical waters; coral reefs support entire animal
communities that rely on the photosynthetic activity of unicellular zooxanthellae that live within the coral polyps; no other ecosystem other than the tropical rain forest rivals coral reefs in terms of complexity and productivity. Zoology textbooks often include a fourth class of cnidarians known as the box jellyfishes (class Cubozoa). These jellysish have a characteristic squarish medusa. The class Cubozoa includes the deadly Australian sea wasp (Chironex fleckeri). If deadliest venom is measured by how long it takes a person to die, then this species is certainly one of the world's deadliest. Depending on the extent of envenomation, the sea wasp can inflict excruciating stings that may cause death within five minutes. Ingenious Australian swimmers and snorkelers have devised a complete nylon body suit made from two pairs of panty hose, one put on the usual way; and the other put on over the hands, arms, and torso, with a slit for the head. Curiously, the deadly nematocysts of Chironex do not sting through panty hose, but watch out for runs! The toxin of jellyfish nematocysts is a complex mixture of proteins, enzymes, polypeptides and tetramine. Pain and local histamine release of some jellyfish stings are attributed to 5-hydroxytryptamine, one of the ingredients in the stinging trichomes of nettles. The mechanism causing cardiac and respiratory failure of sea wasp venom is unclear. It may be due to blockage of nerve impulses at the synaptic junctions, similar to the action of curare.
A marine stony coral showing the numerous calcareous chambers that were once occupied by tentacle-bearing polyps. Colonies of stony corals are important reef builders in warm, tropical waters. Reef corals may form (1) fringing reefsextending out to 0.4 kilometers from shore; (2) barrier reefs separated by a lagoon of considerable width and depth from a shore; and (3) atolls or circular reefs that encircle a lagoon of water and not enclosing an island.
A wide variety of marine invertebrates, including sponges, jellyfish, sea anemones,
orals, gastropods and turbellarians harbor within them golden spherical cells termed zooxanthellae. The photosynthetic activity of these symbiotic algal cells is vital to the survival of the individual coral animals and to the entire reef ecosystem. The zooxanthellae include several species of unicellular algae in the order Zooxanthellales within the algal division Pyrrophyta (also spelled Pyrrhophyta). The term zoochlorellae refer to several species of symbiotic unicellular green algae of the division Chlorophyta. Along the Pacific coast of North America, zoochlorellae produce the greenish color in sea anemone tentacles.
A pristine tide pool along the Oregon coast of North America. A. Purple sea urchin, B. Blood Starfish, C. Coralline red algae, D. Six-rayed starfish, and E. Sea anemone. The tentacles of the sea anemone contain zoochlorellae, symbiotic green cells of the algal division Chlorophyta. Small, brightly colored fish called damselfish or anemone fish have evolved a mutualistic symbiotic association with large sea anemones. A slimy, mucus coating on the fish's body in some way inhibits the discharge of nematocysts along the sea anemone's tentacles. These little fish gain protection from predators by swimming down among the tentacles. The anemone benefits from its symbiont's movements, which dislodge silt and attract other fish into the lethal thicket of tentacles.
A sea anemone and its symbiotic anemone fish.
Phylum Ctenophora (Comb Jellies)
Solitary marine animals with transparent biradially symmetrical bodies; externally there are eight plates of fused cilia that resemble long combs; the rows of ciliated comb plates are used for locomotion; most of the body is composed of a jellylike material called mesoglea; the digestive (gastrovascular) cavity has branched canals; unlike the coelenterates, comb jellies do not have nematocysts; an Atlantic coastal species (Mnemiopsis) exhibits bioluminescence, the emission of light by on organism or population of organisms. This phenomenon involves the oxidation of luciferin in the presence of ATP and the enzyme luciferase. Examples of bioluminesence include dinoflagellates causing "red tide," lightning "bugs" (beetles), glow worms (beetle larvae) and the deep sea angler fish.