The Sponges Phylum Porifera (Latin porous, “pore”; ferre : “to bear”). About 5,500 living species most marine although there are about 200 freshwater species; 30 freshwater species in the US.
Characteristics of Sponges Metazoa: without true tissue. Cellular grade of complexity (Parazoa). Adults asymmetrical or superficially radialy 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 Dermal pores or ostia 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. 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.
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).
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.
The more complex a sponge condition the more particles it can filter from the water column.
Types of Cells I.Pinacocytes II.Porocytes III.Choanocytes IV.Archeocytes (Amoebocytes or Mesenchyme cells)
I. Pinacocytes Cells of the external epithelium Main functions: –Structure –Contraction
II. Porocytes Cells which form pores Function: to allow water flow
III. Choanocytes Line the flagellated canals and chambers. Main function: to create water flow.
Diameter of channels influences water flow velocity. Particles that are captured are in the 2-5 µm range.
IV. Archaeocytes (Mesenchyme) Amoeboid cells which can be non-sessile Found in cellular matrix Main function: –Digestion –Secrete structural components Spongin Spicules
Sclerocyte (Archiocyte) in the process of secreting a spicule
Keeping the mesohyle together Spongin Spines (spicules) –Siliceous –Calcareous
Spongin Fibers of collagen
Spicules Spines, when placed together form a very rigid skeleton
Megascleres and Microscleres m M
Main Groups of Sponges P: Porifera –C: Calcarea –C: Hexactinellida –C: Demospongiae
Calcarea Calcareous sponges Spicules composed of calcium carbonate Small < 10 cm tall
Hexactinellida Glass sponges Some spicules fused to form skeleton Spicules made of glass (Siliceous spicules) six rayed Deep water sponges
Siliceous spicules in Hexactinellida (Triaxon) six rayed spicules.
Demospongiae Common sponges Skeleton is variable –Spicules –Spongin –both Can be large
Siliceous Spiculse in Desmospongia Never six-rayed Megascleres Microscleres
The Big Picture Sponges are metazoans, but don’t have true tissues They are an ancient group (dead end) Three main groups (taxonomic), which fall into three main structural groups Four types of specialized cells *Choanocyte*