Phylum Porifera - Sponges

1. Phylum Porifera - Sponges • Mostly marine, but include some freshwater inhabitants; usually found attached to the substratum in shallow or deep water. • They are sessile; permanently attached to the substrate • Obtain their food by filter feeding

2. General Morphology • The internal cavity is called the atriumor spongocoel • Water is drawn into it through a series of incurrent poresor dermal ostiapresent in the body wall into a central cavity and then flows out of the sponge through a large opening at the top called the osculum

3. Body layers • 1. The pinacoderm -an outer layer of flattened cells called pinacocytes • 2. An inner lining containing flagellated cells (choanocytes) - draw water in through the pores and move out through the osculum; also trap food particles that are suspended in the water. • The water current is also used for gas exchange, removal of wastes, and release of the gametes • 3. Between the pinacodern and the choanocytes is a gelatinous material called mesohyl; contains several different kinds of wandering cells called amoeboid cells • Archaeocytesare amoeboid cells thatphagocytize food particles; they can also undergo differentiation to form other cells, including cells that produce spicules and gametes

4. The Skeleton In the mesohyl is the skeleton composed of tiny pointed structures made of silica or calcium carbonate called spicules. These structures act as an internal scaffolding, but also function in protection Among some sponges the skeleton consist of spongin fibers made of collagenous material; found in many of the commercial sponges

5. Types of Sponges (Canal Systems) • A. Asconoid Sponges • Simple vaselike structure • This stucture puts limitations on size; (increase in volume without a corresponding increase in the surface area of the choanocytes)

6. Types of Sponges (Canal Systems) cont. • B. Synconoid Sponges • The flagellated choanocyte layer has undergone folding forming finger like projections • There is a single osculum but the body wall is more complex, with water being received through incurrent canals, which pass it along to radial canals through to the spongocoel • Results in an increase in the surface area which allowed sponges to increase in the size

7. Types of Sponges (Canal Systems) cont. • C. Leuconoid Sponges • No atrium; several small chambers in which choanocytes are located • There is a whole series of incurrent canals leading to the choanocyte chambers; water is discharges through excurrent canals • The leuconoid sponges exhibit a significant increase in surface area and are, therefore, among the largest sponges

8. Sponge Reproduction • Most are hermaphroditicor monoecious. • Sperm leaves a sponge via the osculum, and enters a sponge by the currents generated from the choanocytes. • Fertilized eggs develop into ciliated free-swimming larvae called parenchymula larvae • Sponges can reproduce asexually by fragmentation • Many of the freshwater sponges can produce asexual bodies called gemmules, aggregationsof cells that are enclosed in hard outer covering containing spicules

9. Sponge Taxonomy • Class Calcarea (Calcispongidae) • Only sponges that possess spicules composed of calcium carbonate. • Spicules are straight or have 3-4 rays, and do not have hollow axial canals. • Today, their diversity is greatest in the tropics, predominantly in shallow waters

10. Taxonomy cont. • Class Hexactinellida (Hyalospongiae) • Glass sponges; characterized by siliceous spicules consisting of six rays intersecting at right angles • Widely viewed as an early branch within the Porifera

11. Taxonomy cont. • Class Demospongiae • Greater than 90 percent of the 5,000 known living sponge species are demosponges. • Demosponge skeletons are composed of spongin fibers and/or siliceous spicules • Siliceous spicules with one to four rays not at right angles, • All members express the leuconoid body form Yellow sponge growing on a wall on a Caribbean reef.