Phylum Porifera - Sponges Kingdom Animalia Phylum Porifera - Sponges

Introduction They are considered animals because they are multicellular, heterotrophic and their cells have no cell walls Less than 2% of species are found in freshwater Are sessile – remain attached to the substrate Are most remarkable for the characteristics they lack than for those they possess Lack a nervous system and have no true musculature Have no organs (digestive, reproductive, respiratory, sensory or excretory) Are amorphous (asymmetrical) Do not have anything corresponding to an anterior, posterior or oral surface

Structure In its simplest form, the typical sponge is a fairly rigid perforated bag whose inner surface is lined with flagellated cells 2 cell layers: (not tissues) Epidermis: A contractile cell layer that allows the sponge to undergo minor shape changes Inner Cell Lining: Composed of choanocytes or collar cells

Evolutionary side bar Choanoflagellates are unicellular organisms that will live in colonies It is hypothesized that they will share a common ancestor with sponges

RELATIVES Recent studies suggest that choanoflagellates are cousins to all animals in the same way that chimpanzees are cousins to humans. From left, a choanoflagellate colony, feeding cells of sponges that resemble choanoflagellates and a choanoflagellate with its long flagellum and collar of filaments. There can be millions of choanoflagellates in a gallon of sea water. Credit Left and Right, Mark Dayel, Center: Scott Nichols

Structure These two cell layers sandwich a middle, jelly-like mesoglea which contains amoeboid-like cells called amoebocytes which perform MANY functions for the sponge This layer also contains support elements called spicules

Spicules - A needlelike structure made of silica or calcium carbonate that, in large numbers, makes up the supporting framework of various sponges.

Cell Types Ectoderm - Contractile cells that allow for minor shape changes Choanocytes/collar cells - The collars of sponge choanocytes are almost certainly homologous with those of choanoflagellates Amoebocytes – wander through the mesoglea and perform a number of essential functions Porocytes – Allow water to flow from surrounding environment to the inside of the sponge

Functions of Choanocytes To generate currents that help maintain circulation of seawater within and through the sponge To capture small food particles To capture incoming sperm for fertilization

Functions of Amoebocytes Digest food captured by choanocytes Store digested food Give rise to both sperm and egg cells Play a role in eliminating wastes Specialized cells secrete the supporting elements located in the mesogleal layer (spicules) Produce dormant structures called gemmules in freshwater species when conditions are unfavourable

Locomotion Adults are sessile Larva = mobile

Ingestion, Digestion and Elimination Sponges filter the water they pass through themselves for phytoplankton and zooplankton: Collar cells beat flagella creating a current bringing in water through ostia Mucus on the collars trap food where it is ingested by endocytosis Some of the food is digested within food vacuoles in the choanocytes, some is transferred to the amoebocytes

Ingestion, Digestion and Elimination Amoebocytes transport nutrients to other cells of the body Waste materials are enclosed in a waste vacuole and leave the cell body (they are then eliminated into the spongocoel, where they leave the sponge Excretion consists of the diffusion of nitrogenous wastes out of the cells

Respiration Respiration is through direct diffusion (Remember, no organs!!!!) Oxygen diffuses from the water into the cells Carbon dioxide difuses from the cells to the water

Reproduction Asexual By fragmentation or budding Freshwater species produce gemmules (These have the same function as endospores in bacteria) Gemmules are a clump of spicules and food-laden amoebocytes covered in a tough protective coat Gemmules of some species have hatched successfully after 25 years of storage

Reproduction Sexual Some species of sponges have separate sexes Other sponges have both sexes and are hermaphrodites Sperm and egg are produced by the amoebocytes Sperm are released out of the osculum and are carried by water current to other sponges, where they enter the ostia and are caught by choanocytes The sperm are transferred to the amoeboid egg cell where they are fertilized internally Zygotes develop into flagellated larvae which break loose and are dispersed by the water currents

Ecological Importance Provide habitats for other animals (eg. Snails, sea stars, shrimp, rockfish

Ecological Importance Are a source of food for other animals (snails and small fish) Provide camouflage for small animals (Decorator crabs often have sponges growing on their shells) Many species are involved in symbiotic relationships with photosynthetic organisms

The Sponge Decorator Crab

Ecological Importance Help clean up the ocean floor by boring into dead shells and corals, releasing chemicals to break them down

Economic Importance Used commercially for bathing/cleaning sponges (although artificial sponges have replaced the need for a large fishery) Many sponges produce toxins as a defense against predators. These toxins are used in cancer and viral research, along with antibiotic research