Porifera

The phylum Porifera (the sponges) includes about 5000 species almost all of which are marine (there are about 150 freshwater species, members of the family Spongillidae). Porifera means “pore-bearing” and refers to the numerous pores and channels that permeate a sponge’s body.

Yellow Tube Sponge Barrel Sponge

Have a cellular level of organization lacking true tissues and organs. Sponges are the simplest multi-cellular organisms, but they lack the germ layers of more complex metazoans. Have a cellular level of organization lacking true tissues and organs. Body is a mass of cells imbedded in a gelatinous matrix (mesohyl) which is supported by a framework of spicules, as well as collagen and spongin fibers.

Porifera Feeding Sponges are sessile (they don’t move) and depend on water movement to bring in food and oxygen and remove wastes. Sponges generate their own flow of water having a unique water current system

Water enters through many small pores called ostia and exits through fewer, larger oscula.

Openings are connected by a series of canals, which are lined by choanocytes (the flagellated collar cells) that maintain the current and filter out food particles. Sponges can filter enormous volumes of water as much as 20,000 times the volume of the sponge in 24 hours. Sponges mostly consume bacteria and may filter as much as 90% of those passing through.

Types of cells Sponge cells occur scattered through a gelatinous matrix called mesohyl. Spicules are distributed through the mesohyl as are several different specialized cells types

Archaeocytes: move around within the mesohyl Archaeocytes: move around within the mesohyl. They are ameboid in appearance and carry out several tasks. Phagocytize particles and receive particles for digestion from choanocytes. Can differentiate into other specialized cell types. Secrete structural components.

Choanocytes: (collar cells) engage in filter feeding Choanocytes: (collar cells) engage in filter feeding. One end is imbedded in mesohyl and the other end protrudes. The protruding end of the choanocyte has a flagellum that moves water through a mesh-like collar where small particles are trapped.

Porocytes: These are tubular cells that in the simplest type of sponge (asconoid sponges) form tubes through the wall of the sponge and allow water to flow into the central chamber.

Canal systems Most sponges have one of three types of canal system: Asconoid Syconoid Leuconoid These systems differ from in each other in the increasing complexity.

Asconoid Asconoid is the simplest system. Water enters through pores into a single large central cavity (the spongocoel) which is lined with choanocytes. There is a single large osculum.

Syconoid In syconoid canal systems there is still a single spongocoel and osculum, but the lining of the spongocoel is folded back to make radial canals lined with choanocytes.

Leuconoid Leuconoid organization is most complex and permits an increase in sponge size. Most leuconoids form large masses with numerous oscula. Clusters of choanocyte-lined chambers receive water from narrow incurrent canals and drive water into excurrent canals that eventually reach the osculum. There is no spongocoel.

Sponge reproduction Sponges reproduce both sexually and asexually. Most sexually reproducing species are hermaphrodites (individuals produce both male and female gametes at different times). Sperm are shed into the water and taken up by other sponges. Individuals with eggs use special cells called archaeocytes to transport sperm to the eggs.

Zygotes develop into ciliated larvae that are released into the water and eventually settle and develop into a sponge. Asexual reproduction is either by budding or more commonly the production of gemmules which are clusters of cells surrounded by a protective coat

Classes of Sponges There are three classes of sponges: Class Calcarea Class Hexactinellida Class Demospongiae

Calcarea Calcareous sponges whose spicules are made of calcium carbonate. Tend to be small (<10cm) and tubular or vase shaped. May be asconoid, syconoid or leuconoid in structure.

Hexactinellida (glass sponges) Skeleton is made of six-rayed siliceous spicules bound in a glasslike lattice. Nearly all are deep sea forms. relatively uncommon and are mostly found at depths from 450 to 900 metres (1,480 to 3,000 ft)

Demospongiae The Demospongiae includes about 80% of all species and includes the freshwater Spongillidae. Spicules siliceous, spongin or both. Includes the bath sponges, which have only spongin skeletons.