Sponges are animals that do not have heads, arms and internal organs. The adults do not move about like other animals. They are attached to objects such as rocks and plants under water, so they are called sessile animals . Sponges differ in size, color and shape. The smallest sponges are less than three centimeters in diameter, while the largest are more that one meter in diameter. The most common color of sponges is green. There are yellow, purple, orange, gray and black sponges. Some sponges are shape like a vase. There are also round ones. Some sponges have theshape of object of which they are attached. Sponges are radially symmetrical . This means that their body can be divided into two equal parts by cutting through the center in any direction.
The body of a sponge has many pores . Sponges are aquatic invertebrates with bodies full of pores. Water enters the spore's body through these pores. Tiny plants and animals in the water are the sponge's food. Waste products from the sponge's body come out through these pores also. Some sponges have tiny, hard skeletons called spicules . Others have a flexible skeleton called sponging containing protein. Sponges commonly reproduce asexually. In asexual reproduction , buds grow on the parent sponge. Most sponges have the ability to replace lost body parts or two repair damaged body parts. This process is known as regeneration .
Aquatic animals with soft bodies shaped like a vase, a bell oran umbrella belong to the group known as cnidarians. Cnidarians were formerly called coenlenterates . The parts of its body are arranged like a vase. These are called polyps . Others are shaped like a bell or umbrella. These are called medusae (plural or medusa). Cnidarians are aquatic invertebrates with hollow and radially symmetrical bodies provided with tentacles.
The hydra is an example of a polyp. It is a very tiny and transparent freshwater animal. It is often attaches itself to the plants in a pond. Its mouth is surrounded by tentacles which trap tiny animals and plants for food. A hydra usually reproduces asexually by forming buds on the surface of the parent hydra. Some kinds of hydra are hermaprodites. They are capable of producing both eggs and sperm.
Corals are also polyps. They grow in colonies. Corals feed on tiny larvae of animals and on algae. Adult coral polyps grow buds which later on separate from the parent. The limestone skeletons of coral polyps form coral reefs. The sea anemone is another cnidarian that exist only as polyps. The jellyfish is an example of a medusa . It has a ring of muscles around its edge. When these muscles contract, the jellyfish moves forward. When the muscles relax, the jellyfish moves downward. The jellyfish feeds on plankton and tiny fish.
note: originally posted at Exposeknowledge.com under the same author.