Sponges and Cnidarians

Sponges

Where are sponges found?

Most sponges are found in the sea or salt water. There are, however, a few sponges that are found in fresh water.

What is a Sponge?

Sponges are the simplest of all animals. Sponges have evolved from flagellated protists. Sponges have neither nerves nor muslces, even though their individual cells can both sense and react to various changes it their environment. The cell layers of a sponge are not true tissues but loose organizations of cells. As a sponge turns into its adult form, the sponge becomes sessile meaning that it cannot move to avoid predators. Therefore, sponges have excellent defensive systems in which their toxins and antibiotics keep away pathogens, parasites, and other predators. The antibiotics sponges produce, however, are used for human drugs.

Two different types of sponges

Simple Sponge

• Thick-walled sac perforated with holes
• Water is drawm through pores into central cavity and flows out through a larger opening

Complex Sponge

• Simple sponge with branching water canals

Sponge Body

Sponges are made up of two layers seperated by a gelatinous region. The inner layer is made up of flagellated cells known as choanocytes, which help sweep water through the body of the sponge. The middle layer is called the amoebocyte, which produces supportive skeletal fibers. These fibers are composed of proteins called spongin and mineralized particles of spicules. Sharp spicules protect the large opening at the top of the sponge. Most sponges have both spogin and spicules, however, bath sponges only have spongin.

How do sponges eat?

Sponges use suspension feeders to feed themselves. These suspension feeders are filter feeders, which collect and trap particles from the water. Suspension feeders are made up of choanocytes that trap the food particles in the mucus on the membranous collars that surround the base of flagella. Then, by using phagocytosis, the sponge engulfs the food and the ameobocytes pick up the food vacuoles and carry the nutrients to other cells.

Cnidarians

Cnidaria Classification

Clade Eumetazoa

Part of the oldest phylum: Phylum Cnidaria--consists of hydras, jellies or jellyfish, sea anemonies, and corals--

Characteristics of Cnidarians

Radially symmetrical and Cnidarians only have two tissue layers

Two different types of radial symmetry

Usually Cnidarians are either in a polyp or a medusa stage, but some be in both stages

Polyp

• A cylindrical body with tentacles projecting from one end
• Stationary
• Mouth is located on the top of the body in the hub or the middle of the radiating tentacles

Medusa

• An umbrella shaped body with a fringe of tentacles around the lower edge
• Move freely in the water
• Mouth is located in the center of undersurface

Cnidarian Body

Cnidarians are contractile tissues and nevers in their simplest forms. Made up of an outer epidermis, either a thin jelly-like exterior or a hard coral one, and an inner cell layer that lines the digestive cavity. The middle region is "jelly-filled" and is made up of scattered amoeboid cells. Cnidarians are named for their stinging cells known as cnidocytes.

How do Cnidarians eat?

Cnidarians are carnivors that eat small animals and protists. They use their tentacles to push food into their mouth, which then travels to the gastrovascular cavity to be digested. The gastrovascular cavity acts as a hydrostatic skeleton, porividing body support with the production of fluid.

Source: "Biology: Concepts and Connections, 6th Edition"