Sponges – Phylum Porifera (Pore-bearing) Section 28.1

Basic Characteristics Asymmetrical Bodies do not have tissues or organs: just specialized cells embedded in a gel-like substance called mesohyl Cells demonstrate cell recognition

Body Plan Body is sessile – remains attached to solid surface their whole lives Body wall surrounds a large central cavity Body wall is full of holes – ostia  water in and oscula  water out

Structure of a Sponge

Feeding The lining of the body cavity has cells with flagella – choanocytes (collar cells) The flagella move and create a current for water to enter the ostia Choanocytes filter food from the moving water Food is digested intracellularly Oxygen diffuses into the cells from the water, wastes diffuse from the cells into water Choanocytes release nutrients from digested food into mesohyl and amoebocytes carry it to all the other cells

Sponge Skeletons Most sponges have an internal skeleton made of spicules – needles composed of silica (glass) or calcium carbonate (rock) Some have a flexible protein called spongin Some contain both Three types: 1. Calcareous sponges – calcium carbonate 2. Glass sponges – silica 3. Demosponge sponges – silica and spongin

Sponge Reproduction Asexual reproduction: 1. Regeneration – broken pieces can form new sponges – this is called fragmentation 2. Budding – a small section grows and breaks off, forming a new sponge 3. Gemmules – amoebocytes in protective coats with food – freshwater sponges do this when conditions are too dry or too cold Sexual reproduction: Hermaphrodites – sponges make both eggs and sperm, but at different times in their life cycle to prevent self-fertilization Sperm are released into the water and fuse with egg cells in another sponge – free-living larva swim in the water for a time before landing on an object and growing into adults

Sexual Reproduction in Sponges