Phylum Porifera Ms. Adams’ Zoology

Introduction to Sponges Diversity of species: About 8000 species Phylum Porifera From Greek ‘poros’ meaning ‘passage’ or ‘pore’ Sponges have tiny openings all over their body, hints the name ‘pore-bearers’ Most ancient and primitive of all animals Most sponges are marine, some live in freshwater

Introduction to Sponges Sponges were once thought to be plants because they are sessile, but they are multicellular animals. Sponges are different from other animals: Do not have a mouth or digestive tract (gut) No true tissue layers (endoderm, ectoderm, mesoderm) or organ systems Biologists think that sponges evolved from single-celled ancestors separately from all other animals The evolutionary line that gave rise to sponges was a dead end. It produced no other living groups.

Form and Function in Sponges Sponges do not have true systems, but the following structures fulfill the sponges needs (next slide):

Form and Function in Sponges Four Cell Types: Epidermal cells: flat cells form outer covering (respiration and excretion) Pore cells: water and other substances enter through these cylindrical cells Collar cells: make up inner cell layer Have collar of microvilli Have a flagellum: They wave these to maintain a steady current that draws water in through pores.

Form and Function in Sponges Amoebocytes: amoeba-like cells that crawl around the jellylike inner layer (using pseudopodia) and deliver food and O2 to other cells Amoebocytes absorb nutrients and remove wastes. Amoebocytes make spicules and create a sponge skeleton.

Form and Function in Sponges Amebocytes make thin, spiny spicules from either chalklike calcium carbonate (CaCO3) or glasslike silica (SiO2). These spicules form the delicate skeleton of the sponge. Softer sponges (e.g. natural bath sponges) consist of fibers of a protein called spongin (more flexible than spicules) Some sponge skeletons are made up of both spongin and spicules.

Form and Function of Sponges Sponges are filter feeders. They sift microscopic food particles from the water that passes through them. All the digestion in sponges is intracellular (takes place inside cells). Food particles in water stick to collar cells. Food can either be engulfed by the collar cells and digested (endocytosis) or passed on to the amoebocytes and digested. The amoebocytes deliver digested food to other parts of the sponge.

Form and Function of Sponges The water flowing through a sponge serves as its respiratory, excretory, and circulatory system. Osculum: Water exits out of this hole

Reproduction Sponges use the “broadcast method” of reproduction Sexual reproduction: Sponges are hermaphrodites (have both male and female reproductive parts). Sperm is released from collar cells in sponge A. Sperm then enters pores of sponge B. Fertilization occurs inside of sponge B (amoebocyte carries sperm to egg). Flagellated larvae develop and leave by the osculum. They drift off and settle elsewhere.

Reproduction 2. Asexual reproduction Budding: Small growth falls off of sponge and grows a new sponge Gemmules: Sphere-shaped collections of amoebocytes surround the spicules. They leave sponge, settle, and wait for improved conditions.

Three Sponge Body Forms Ascon: simplest and least common sponge body form. They are vaselike. Ostia (outer openings) lead directly to a chamber called the spongeocoel. Choanocytes line the spongeocoel and draw water into the spongeocoel through the ostia. Water exits through the osculum, a single large opening at the top.

Three Sponge Body Forms Sycon: sponge walls appear folded Water enters through openings called dermal pores. Dermal pores are the openings of the body wall, called incurrent canals. Incurrent canals connect to radial canals, which lead to the spongeocoel. Choanocytes line radial canals (not spongeocoel) and move water from the ostia, through the incurrent and radial canals, to the spongocoel, and out the osculum.

Three Sponge Body Forms Leucon: branched canal system Water enters through ostia and moves through branched incurrent canals, which lead to choanocyte-lined chambers. Canals leading away from the chambers are called excurrent canals. Proliferation of chambers and canals has resulted in the absence of a spongeocoel and multiple exit points (oscula) for water leaving the sponge.

Three Classes of Sponges Phylum Porifera Class Calcarea Class Demospongiae Class Hexactinellida Sclerospongiae is no longer considered a class.

Class Calcarea Have spicules made of calcium carbonate and are needle-shaped or have three or four rays. Ascon, leucon, or sycon body forms. Strictly marine.

Class Demospongiae (Most sponges) Brightly colored sponges that include one freshwater sponge and all bath sponges. Have spicules made of silicon dioxide (SiO2) or spongin or a combination of both. Most sponges belong to this class. (90%) Nearly all are leucon body form.

Class Hexactinellida (Glass sponges) Usually found in deep water on soft substrates in the tropical West Indies at approximately 450 to 900 meters in depth. Spicules are six pointed and have a lattice-like structure. They are made of silica. Cup, vase or urn shaped. Sycon or Leucon body form.