Porifera

PORIFERA

 

-9000 species

 

-Characteristics over head

 

-Classification

-Thin, flat cell, called pinacocytes, line the outer surface of a sponge.

 

-Pinacocytes may be mildly contractile, and their contraction may change the shape of some sponges.

 

-can be modified into contractile porocytes, which can regulate water circulation.

 

-Just below the pinacocyte layer of a sponge is a jellylike layer referred to as the mesohyl.

 

-Amoeboid cells are found moving about in the mesohyl and are specialized for reproduction, secreting skeletal elements, transporting food, storing food, and forming contractile rings around openings in the sponge wall.

 

-Below the mesohyl and linin g an inner chambers are the chanocytes, or collar cells. Chanocytes are flagellated cells that have a collar-like ring of microvilli surrounding a flagellum.

 

-the flagellum creates water currents through the sponge, and the collar filters microscopic food particles from the water.

 

-Sponges are supported by a skeleton that may consist of microscopic needlelike spikes called spicules.

 

-spicules are formed by ameboid cells, are mad of calcium carbonate or silica, and may take on a variety of shapes.

 

-The life of a sponge depends on the water currents created by chanocytes. Water currents bring food and oxygen to a sponge and carry away metabolic and digestive wastes.

 

-The simplest and least common sponge body form is the ascon.

 

-Ostia are the outer openings of porocytes and lead directly to a chamber called the spongocoel.

 

-Water exits the sponge thorough the osculum

 

-The sycon body form the wall appears folded.

 

-Water enters a sycon sponge through openings called dermal pores.

 

-Dermal pores are the opening of invagination of the body wall, called incurrent canals.

 

-Pores in the body wall connect incurrent canals to radial canals, and the radial canals lead to the spongocoel.

 

-Chanocytes line radial canals

 

-Leucon sponges have an extensively branched canal.

 

-Proliferation of chambers and canals has resulted in the absence of a spongocoel, and often multiple exit points (oscula) for water leaving the sponge.

 

-In complex sponges, an increased surface area for chanocytes results in large volumes of water big moved through the sponge and greater filtering capabilities.

 

-Although the evolutionary pathways in the phylum are complex and incompletely described, most pathways have resulted in the leuconoid body form.

 

-Sponges feed on particles that are in the 0.1 to 50 µm size range - bacteria, microscopic algae, protists, and other suspended organic matter.

 

-Large populations of sponges play an important role in reducing turbidity of coastal waters.

 

-A single leuconoid sponge, 1cm in diameter and 10 cm high, can filter in excess of 20 liters of water every day.

 

-Food is trapped on the collar and moved along microvilli to the base of the collar, where it is incorporated into a food vacuole.

 

-Digestion begins in the food vacuole by lysosomal enzymes and pH changes

 

-Filtration is not the only way that sponges feed, larger food particles may be phagocytized by pinacocytes lining incurrent canals.

 

-Sponges do not have nerve cells to coordinate body functions. Most reactions are the

result of individual cells responding to a stimulus.

 

-Nature of communication is unknown.

 

-Most sponges are monoecious (both sexes occur in the same individual)

 

-Certain chanocytes lose their collars and flagella and undergo meiosis to form flagellated sperm.

 

-Sperm cells exit one sponge through the osculum and enter another sponge with the incurrent water.

 

-early development occurs in the mesohyl.

 

-Cleavage of a zygote results in the formation of a flagellated larval stage.

 

-After no more than two days of free swimming existence, the larva settles to the substrate and begins development of the adult body form

 

-Some sponges possess remarkable powers of regeneration.

 

-Portions of a sponge that are cut or broken from one individual will regenerate new individuals.