PORIFERA Belong to the subkingdom Parazoa Latin for

PORIFERA • Belong to the subkingdom Parazoa • Latin for “pore-bearing” • Phylum comprised of sponges

Symmetry

Germ Layers • Porifera lack distinct tissues and organs and, therefore, have no germ layers. • Porifera do have two cellular layers. - Pinacocytes: line the outer surface - Choanocytes: line the interior body

Level of Organization • Porifera have the cellular level of organization. • Cells are specialized to perform different functions, but are not organized into tissues or bodies. • Porifera do not have nervous systems.

Body Cavity Porifera are acoelomates: they have no body cavities. Segmentation Porifera are nonsegmented.

Body plan Asconoid – simplest form, tube or vase shaped, no canals Syconoid – radial canals, more choanocytes, can filter more water Leuconoid – largest, most complex, most numerous, incurrent canals which open into chambers lined with choanocytes Yellow – pinacocytes Red – choanocytes Gray – mesophyl

Subgroup – Hexactinellida • • Composed of siliceous spicules (silicon dioxide) Six rays intersecting at right angles Only leuconoid forms Approximately 500 living species • Cannot contract • Conduct electrical pulses across their bodies • Oscula notably large

Subgroup - Demospongiae • Composed of siliceous spicules and/or spongin fibers • 1 -4 rays, not at right angles • Only leuconoid forms • Approximately 4750 living species • Most diverse group – variety of growth forms • Tend to be large • More than 90% of Porifera are classified as Demospongiae

Subgroup - Calcarea • • Composed of calcareous spicules (calcium carbonate) 3 -4 rays Has asconoid, syconoid, and leuconoid members Approximately living 400 species • Often rough textured • Usually small in size

Subgroup - Sclerospongiae • Composed of siliceous spicules, spongin fibers, and calcium carbonate • Only leuconoid forms • Few living species, found only in the West Indies and Pacific • Resemble corals • Contribute to the structure of reefs

Habitat • All porifera are aquatic • Most are marine (only 150 freshwater species) • While hexactinellida live at great depths, calcarea are predominantly found in shallow waters • Demospongiae live in a variety of aquatic environments • Porifera may live independently or in colonies • Porifera are sessile: they attach themselves to rocks, coral, shells, and other substrates

A - require exposed surface - elevated form provides good access to water - attachment area is small portion of total body surface B - use much of surface for attachment - low form allows for crevice dwelling C - utilizes space in the substrate

Asexual Reproduction • Budding - Mitotic cell divisions produce a bud that is pinched off from the parent • Fragmentation - Offspring is formed from a segment of the adult body • Gemmule Formation – Occurs in freshwater sponges; internal buds called gemmules are formed within the adult body and eventually develop into individuals

Sexual Reproduction - Hermaphroditic Each adult possesses both male and female sex organs and can act as either sex in the process: 1. Spermatozoa are released into the water by a sponge and taken into the pore systems of a neighbouring sponge 2. The spermatozoa are captured by choanocytes which then transform into specialized cells that carry the spermatozoa to the eggs 3. The fertilized eggs are released into the water 4. The larvae may settle immediately or may drift for some time

Suspension Feeding • Choanocytes contain flagella that drive water through the sponge, trapping bacteria and other food • Nutrients are distributed among the cells of the mesohyl that facilitate the functioning of feeding, respiration, and reproduction • The flow of water inside a sponge in unidirectional: water is drawn in through tiny pores called ostia and exits through large openings called oscula • The water flow not only provides food, but also oxygen and means for waste removal

• • • Amoebocyte – functions in digestion Choanocyte – lines interior body Flagellum – creates current of water Mesohyl – gelatinous layer Osculum – large exterior opening; water outlet • • • Ostium – small exterior pore; water inlet Pinacocyte – lines outer surface Porocyte – tubular cell, constitutes a pore Spicule – skeletal component, provides support Spongocoel – central chamber

Exception - Cladorhizidae • These carnivorous sponges feed by capturing and digesting small crustaceans Harp sponge – barbed hooks

Regeneration • If the cells of a sponge are separated, they can reassemble and regenerate into a complete and functioning organism Regeneration video