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Phylum Porifera Pronounced (po-rif'-er-a) The name means “bearing pores” Sponges are made up of a system of tiny pores and canals that make up a intricate filter feeding system. Sponges are sessile, meaning they have a stationary, inactive lifestyle. Their bodies are made up of thousands of cells mixed together in a gel-like mixture, supported by small structures called spicules made of calcium carbonate or silica and collagen.
Phylum Porifera Because they are sessile, they are highly dependent on ocean currents to bring food to them and eliminate waste products. They have no organs or true tissues. Digestion is intracellular. Respiration and excretion occurs by simple diffusion. No nervous system. Sponges are asymmetrical. There are three main classes of sponges; Calcarea, Hexactinellida, and Demospongiae.
Sponge Ecology There about 5000 sponge species. About 97% are marine, 3% freshwater. Embryos are free-swimming. Adults are always attached to other objects. (rocks, corals, submerged objects etc. ) Many other organisms such as crab and fish live symbiotically in or on sponges. Some sponges live on other organisms like molluscs and corals.
Diversity of Sponges
Sponge Anatomy and Physiology Their bodies are made of numerous tiny pores called Ostia that allow water to flow into a sponge. One to several large openings that allow water to flow out of a sponge are called Oscula. A singular Oscula is called an Osculum. Small cells that line the canals of a sponge with whiplike flagella are called Choanocytes. The flagella on the choanocytes maintain the flow of water through the canals. The choanocytes also trap food particles.
Sponge Anatomy and Physiology
Sponge Canal Systems Sponges have three types of canal systems; Asconoid, Syconoid, and Leuconoid.
Sponge Canal Systems
Asconoid Sponges (Flagellated Spongocoels) Asconoids have the simplest body plan of the sponges. They are small and tube shaped. Water enters the ostia into a large cavity called the Spongocoel. The choanocytes then expel the water out the osculum. Asconoids are found only in the class Calcarea.
Asconoid Sponges (Leucosolenia sp. )
Syconoid Sponges (Flagellated Canals) Similar to Asconoids. Water is expelled through one large osculum like in the asconoids. Choanocytes do not line the spongocoel. The choanocytes line individual canals along the sides of the body tube called radial canals. Syconoids are mostly found in class Calcarea. Some are also found in class Hexactinellida
Syconoid Sponges (Sycon sp. )
Leuconoid Sponges (Flagellated Chambers) The Leuconoid body plan is the most complex. Their unique body design allows for a much greater body size. The increased body size increases the amount of flagellated choanocytes, therefore increasing the amount of food that can be consumed. Most leuconoids are large masses rather than simple tubes, with numerous oscula. There is no spongocoel in leuconoids. They are found in all three classes of sponge.
Cellular Structure of Sponges The connective tissue of sponges consists of a loose gel-like mixture called Mesohyl. The epithelial cells of sponges are called Pinacocytes. These cells play a role in trapping food particles. Porocytes make up the ostia that allow the passage of water into the sponge. Archaeocytes are cells in the mesohyl that perform a variety of functions such as digestion and production of spicules and collagen.
Cellular Structure of a Sponge
Sponge Skeletons An important structural protein in the animal kingdom and in sponges is called collagen. Thin strands of collagen are found throughout the bodies of sponges. The class of Demospongiae produces a form of collagen known as spongin. Various forms of spicules are found throughout the different classes of sponges. They are made up of Silica or Calcium Carbonate.
Sponge Skeleton Spicules on the left Spongin on the right
Sponge Metabolism As mentioned earlier, various sponge cells such as choanocytes and pinacocytes aid in digestion by trapping food particles. The primary cell type that actually metabolizes the food are the archeocytes. Respiration and excretion occur by diffusion. All metabolic activities are highly dependent on a constant flow of water from ocean currents. Some sponges filter as much as 1500 liters/day!
Sponge Reproduction Sponges reproduce both sexually and asexually. Most sponges are monoecious. Meaning a single sponge can have both male and female sex cells. Sperm cells develop from choanocytes. Egg cells can develop from choanocytes in some species and from archaeocytes in others.
Sponge Reproduction After fertilization, the zygotes develop into a freeswimming flagellated larva called a parenchymula. Paranchymula break off from the adult sponge and are carried away by ocean currents. Sponges can reproduce asexually by fragmentation (this occurs when a fragment is broken off from the main body of the sponge) and by external budding. Budding occurs when a small sponge grows off of the adult sponge. Eventually these can break off and regenerate.
Sponge Reproduction Asexual reproduction can also occur by the formation of internal buds called gemmules. Gemmules are internal buds that are usually dormant and contain archaeocytes. Gemmules are formed during unfavorable conditions like drought, freezing temperatures, and anoxia for long periods of time. After the unfavorable conditions pass, the archaeocytes can then be released from the gemmules to regenerate into a new sponge.
Sponge Larva and Gemmules Parenchymula on the right. Gemmule on the left
Class Calcarea Spicules of calcium carbonate (calcite and limestone) All three types of canals represented (asconoid, syconoid, and leuconoid). All marine (Clathrina) Class Calcarea
Class Hexactinellida Six-rayed spicules made of silica (same substance as glass) Body often cylindrical and funnel shaped Syconoid or leuconoid All Marine Venus Flower Basket (Euplectella)
Class Demospongiae Skeleton made of silica Very diverse group of sponges spicules that are not six -rayed, or a skeleton made of spongin, or both. Leuconoid type canal systems only. One family freshwater, all others are marine.