Phylum Porifera (Sponges)
Sponges belong to the phylum Porifera in the animal kingdom. The main reasons they are placed into this phylum is due to the presents of numerous holes called pores.
They also lack tissue found in other animals. Many biologists believe sponges are groups of colonial cells living together in one larger structure.
These animals have other characteristics that make them unique members of the animal kingdom. They are filter feeders. Since these animals do not move (sessile) they must gather food by filtering it out of the water as it flows through it. Special cells called collar cells pick up the planktonic food and start the digestive process.
They contain spicules. These structures are small bone like particles made out of calcium carbonate or silicon dioxide. They function in support and protect these animals from danger.
They do not contain any muscle or nervous tissue.
Each cell is in direct contact with the water so its excretory and respiratory functions are taken care of individually by each cell.
They exhibit radial symmetry and in some cases no symmetry at all. Many of them form large colonial groups that serve as havens for fish and other aquatic life.
They reproduce through the process of budding where an adult will grow an offspring from it side. These buds can remain attached to the parent or break off and take up residence elsewhere. Sponges are also know to regenerate lost body parts. Sexual reproduction is limited. Structures called gemmules are formed from amebocytes and spicules during environmental stress.
Many sponges contain a large opening at the top of its body called the osculum. Water is taken into the sponge through its many incurrent pores and circulated out through the osculum.
Sponges contain the protein spongin which acts as a base for the cells to cling to while forming the animal.
1. incurrent pores, 2. osculum, 3. bud
Phylum Cnidaria: (jellyfish, coral, Hydra, sea anemone, Portuguese-man-of-war)
Cnidarians contain 2 body shapes: The polyp which is a cylindrical structure with tentacles at the top of the animal. The medusa is an umbrella shaped structure with its tentacles near the bottom of the animal.
They contain tentacles with special stinging cells called nematocysts. These nematocysts come in a variety of structures. They are activated by touch and can only be used once. They function in protecting the animal and helping capture its food. The cnidocytes are the cells that produce the nematocysts.
They contain 2 cell layers: the ectoderm or outer cell layer and the endoderm the inner cell layer.
These 2 layers are separated by a jelly-like layer called the mesoglea.
Within the mesoglea we find a nerve net. These organisms do not contain a brain. .
They contain a central cavity called the Gastrovascular cavity. Digestion takes place here and the contents are absorbed by the endodermal cells. The undigested food is expelled through its mouth. This is considered a two way digestive process.
They contain radial symmetry. Some organisms are sessile while others are free floating.
They reproduce by budding and regeneration. They also reproduce sexually. They contain both male and female reproductive structures in the same body. They are neither male or female, they are called hermaphroditic.
Many of these organisms are marine though some (Hydra) are fresh water .