Exercise 2b - Phylum Porifera

Cards (29)

  • The name Porifera (L. porus, pore + ferre, to bear) refers to the porous structure of the body with many surface openings.
  • Sponges are the most primitive multicellular animals in that their cells function independently, with no coordination via a central nervous system, and they do not form true tissues nor organs. Their metabolism is largely dependent on the flow of water through its dermal pores and inner canals, thus they are exclusively aquatic and chiefly marine. They are sessile animals, and are often found attached to rocks, submerged timber, corals and the shells of other animals.
  • What are the three Classification of Porifera?
    Class Calcarea, Class Hexactinellida, and Class Demospongiae
  • Class Calcarea - Exclusively marine sponges with skeleton entirely calcareous spicules, which are either needle-shaped or 3- or 4- rayed. All three types of canal system represented, spicules not differentiated into megascleres and microscleres.
  • Class Hexactinellida – Exclusively marine usually deep-sea glass sponges with skeleton of 6-rayed siliceous spicules extending at right angles from a central point and united to form a network; body often cylindrical or funnel-shaped; exhibit syconoid or leuconoid arrangement, megascleres and microscleres present.
  • Class Demospongiae – Marine or freshwater sponges with skeleton of siliceous spicules, or sponging fibers or both, megascleres monaxon or tetraxon (never 6-rayed); microscleres of diverse types, leuconoid canal system.
  • Body Organization
    The body of sponges is beset by numerous tiny openings such as many tiny pores called ostia for incoming water, and one to several larger oscula for water outlet.
  • The exterior surface of the sponge is covered by the dermal pinacoderm and is composed externally by a thin layer of flat cells called pinacocytes.
  • Incurrent pores, called ostia, on the outer surface of the sponge lead into the incurrent canals which end blindly near the inner surface of the body wall.
  • These incurrent canals are connected to the radial canals by small pores called prosopyles.
  • The choanoderm lines the radial canals and is made up of a single layer of collared, flagellated cells, the choanocytes.
  • The radial canals then lead into the large central canal, the spongocoel, through minute pores called apopyles.
  • Between the pinacoderm and the choanoderm is a gelatinous matrix called the mesohyl which contain amoebocytes, which are roaming cells that carry many functions, including distributing food to other cells, reproduction and production of the sponge’s skeleton.
  • What are the two skeletal system under phylum Porifera?
    Spicules and Spongin
  • Spicules
    One such element is the spicules which may either be calcareous or siliceous in composition. They exhibit a wide variety of forms, size and degree or ornamentation.
  • Spongin
    Various members of Class Demonspomgiae secrete an insoluble, sulphur-containing form of collagen known as sponging. This component usually occurs as interwoven fibers.
  • Reproduction
    Sponges reproduce both sexually and asexually. Asexual reproduction in freshwater sponges and some marine forms is achieved by the formation of gemmules. It is a hollow, cyst-like ball of archeocytes/amoebocytes. It is covered with a tough coat of sponging.
  • What are the samples under Class Calcarea?
    Leucosolenia and Sycon
  • Leucosolenia - This calcareous sponge occurs in clusters or colonies in shorewaters.  The body is tubular and opens at the tip through the osculum. This opening leads to a cavity, the spongocoel that is lined with many choanocytes. The wall is made up of flattened cells, the pinacocytes.
  • Sycon (=Grantia, Scypha). This marine sponge is gray or light brown in color when fresh. It grows to only about 23 cm and occurs as a colony of several cylinders attached at the base.
  • Class Hexactinellida
    Euplectella (Venus flower basket) - This syconoid deep-sea glass sponge has a cylindrical and curved body.
  • Euplectella (Venus flower basket)
    The openings in the meshwork of 6-rayed spicules are called parietal gaps.
  • Projecting from the surface of the sponge are feather-duster like spicules called floricomes.
  • The root spicules attached the sponge to the substratum.
  • What are the samples under Class Demospongiae?
    Spongia (bath sponge), Spongilla, Carteriospongia (Elephant's ear sponge), and Xestospongia (barrel sponge).
  • Spongia (bath sponge) - The bath sponge belongs to the group called horny sponges
  • Spongilla - The greenish-hue of this sponge is due to the presence of symbiotic algae.
  • Carteriospongia (Elephant’s ear sponge) - The main body of this marine sponge consists of a broad leathery plate with a skeleton made up of only sponging and no spicules.
  • Xestospongia (Barrel sponge). Barrel sponges can grow as much as 1.5, high and have volcano- or barrel-shaped bodies with thick knobbed or ridged walls.