The Simplest Life-Forms

Even though some organisms, such as sponges, jellyfish and sea anemones, look like vegetables, they belong to the animal kingdom. Many of these simple invertebrates are unable to move from one place to another; some even lack certain tissues or an entire respiratory or digestive system. Other, more developed species, such as squid and octopus, can move about and have become skilled predators. Cephalopods are the most highly evolve molluscs. Their head have highly developed eyes, a mouth with two hornlike jaws, and tentacles with suckers to trap their prey. Some cephalopods live in deep-sea waters, whereas others stay close to shore.

Radial Symmetry

Mant of the numerous invertebrates on the earth live in the ocean. Some such as polyps and jellyfish, have radial symmetry - that is, their bodies are structured around an axis. A typical echinoderm, such as the starfish, has tiny, flexible, tubed shaped legs arranged like the spokes of the wheel. The animal uses them to hold onto surface and to move. Sponges, on the other hand, are very simple, multiple-celled animals, with many small pores that hey use to feed.

Sea Carnival

Corals and anemones, together with jellyfish, make up the phylum Cnidaria. Some characteristics they share are their bright colours, tentacles that secrete stinging substances and a digestive system with a common opening for ingestion and exretion - the simplest digestive system in the animal kingdom. All of these organisms are quite simple. Corals generally formed colonies, large group of small polyps that stay practically immobile and feed on microorganisms brought to them by water currents. Sea anemones, on the other hand, are solitary and can trap prey despite their limited locomotion.

Aquatic

Chinoderms (phylum Echinodermata) are one of the best-known groups of marine invertebrates. Sea urchins and starfish, despite their apparent differences, are part of the same group and share characteristics such as five-radial symmetry. This phylum has an aquatic vascular system with many amburacral grooves with tube feet, which it uses for locomotion, capturing prey and breathing. In addition, it has an internal skeleton made of calcareous plates. These creatures lack of brain or eyes, so they use photoreceptors to sense movement.

Jointless

The body of most molluscs is soft, extremely flexible and without joints, yet has a large and very hard shell. Most molluscs live in the ocean, but they are also found in lakes and land environments. All modern molluscs have bilateral symmetry, one cephalopod foot with sensory organs and locomotion, a visceral mass and a covering, called the mantel, that secretes the shell. Molluscs also have a very peculiar mouth structure called a radula.

Generating Added Value

Bivalves are sought after and culrivated or their pearls. Pearls are said to be the queen of gems, because they were discovered more than 4,000 years ago and were used as important symbols in many ancient cultures. In spite of their high price, pearls start out as a nuisance for animal that creates them, which could be an oyster, a clam or a mussel. Oysters produce the most valuable pearls, which are noted for their lustre.

Powerful Tentacles

The eight-tentacled octopus is one of the few large cea cephalopods to live in deep water. It is usually found on the rocky or sandy bottoms of shallow waters near the mouths of rivers. It generally moves slowly, sometime moving in brief spurts, but it can reach great speed when hunting or fleeing. Some are quiet intelligent, having highly evolved brains.