Phylum Porifera: Sponges Chapter 6

The Sponges Phylum Porifera (Latin porous, “pore”; ferre : “to bear”). About 5,500 living species most marine although there are about 200 freshwater species.

Characteristics of Sponges Metazoa: without true tissue. Cellular grade of complexity (Parazoa). Adults asymmetrical or superficially radially symmetrical. Unique flagellated cells the choanocytes that drive water through canals and chambers: the aquiferous system. Adults sessile suspension feeders; larval stages are motile. Reproduction sexual or asexual.

The Poriferan Bauplan Two unique organizational attributes: The aquiferous system Highly totipotent nature of sponge cells

Overview of general structures Sponges move water through their bodies using choanocytes All cells are loosely arranged into a gelatinous matrix, the mesohyle Water enters small holes called ostia Water exits large holes called oscula A skeleton helps maintain the structure of the sponge.

Body Structure and the Aquiferous System The mesohyl includes a non cellular coloidal mesoglea in which are embedded collagen fibers, spicules and various cells. Most of these cells are able to change from one type to another as required. Water flows through the ostia all the chanels and eventually out through the osculum. Dermal pores or ostia 3)

Types of Canal Systems Most sponges can be separated based on their type of canal system. 1. Asconoid 2. Syconoid 3. Leuconoid

Asconoid sponges Found in radially symmetrical calcarous sponges: rarely exceed 10cm in height.

Asconoid sponges Simple organization Water moves through the ostia into the spongocoel Choanoderm simple and continuous one cell thick.

Fig. 6.3 Asconoid condition Choanoderm simple and continuous one cell thick.

Fig. 6.3 3 Asconoid water flow 2 1 Water flow: 1) ostium  2) choanoderm  3) osculum 2 1

#1 #2 #3

Syconoid sponges Syconoid condition: simple folding of the pinacoderm and choanoderm. As complexity increases the mesohyl may thicken and appear to have two layers. Water is brought in through the incurrent canals and then to radial canals (lined with choanocytes).

Fig. 6.3 Syconoid condition Choanoderm restricted to chambers with an apopyle opening into the atrium.

Fig. 6.3 Syconoid water flow Water flow: 1) incurent pore  2) incurrent canal  3) prosopyle  4) choanocyte chamber  5) apopyle  6) atrium  6) osculum

Leuconoid sponges Additional folding of the choanoder and further thickening of the mesohyl. Water is brought in through incurrent canals, and discharged through excurrent canals. Most common type.

Fig. 6.3 Leuconoid condition The atrium is reduced to a series of excurrent canals. Water flow: 1) dermal pore  2) incurrent canal  3) prosopyle  4) choanocyte chamber  5) apopyle  6) excurent canal  7) osculum

The more complex a sponge condition the more particles it can filter from the water column.

Types of Cells Pinacocytes Porocytes Choanocytes Archeocytes

I. Pinacocytes Cells of the external epithelium Main functions: Structure Contraction

II. Porocytes Cells which form pores Function: to allow water flow

III. Chanocytes Line the flagellated canals and chambers. Main function: to create water flow.

Codosiga