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• Phylum Porifera: Sponges have specialized cells but no tissues; no symmetry – Sponges are the most primitive animals on Earth • 570 million year old fossils • Closely related to a group of protists – Sponges share common characteristics: • Sessile do not move • Reproduce both sexually & asexually • They are filter feeders – Sponges have several types of specialized cells: • Pinacocytes thin and leathery cells that form a sponge’s outer layer • Choanocytes “collar cells,” form the inner layer of a sponge – Cells have flagella surrounded by a collar of tiny hairlike structures called microvilli – These cells pull water through the sponge by beating their flagella trapping food particles in their mucus. • Ameobocytes mobile cells found in the jellylike material between the 2 cell layers – They absorb & digest food particles caught by their collar cells – Transport oxygen & waste in the sponge • Internal organization of a sponge: pinacocyte choanocyte amoebocyte • Phylum Cnidaria: Cnidarians are the oldest existing animals that have specialized tissues; radial symmetry – Cnidarians have 2 body forms: • Polyps cylindrical tubes with mouth and tentacles facing upward (example – coral) • Medusas umbrella-shaped with their mouth and tentacles on the underside (example – freeswimming cnidarians such as jellyfish) – Cnidarians reproduce both sexually & asexually • Polyps reproduce asexually by budding, producing genetically identical offspring • Medusa reproduce sexually by releasing gametes into the water – Fertilized egg develops into a free-swimming larva called a planula – The planula then develops into the polyp stages • Many cnidarian species alternate between these two body forms Feeding polyp Reproductive polyp Medusa bud ASEXUAL REPRODUCTION (BUDDING) Portion of a colony of polyps Haploid (n) Diploid (2n) Gonad Medusa Egg SEXUAL REPRODUCTION Sperm FERTILIZATION Zygote 1 mm Key MEIOSIS Developing polyp Mature polyp Planula (larva) – Cnidarians are made up of 2 tissue layers separated by mesoglea (noncellular jelly like material) • Outer tissue layer has 3 cell types: – Contracting cells cover the surface of the cnidarian & contain muscle fibers – Nerve cells interconnect & form a network over the entire animal (they do not have brains) – Cnidocytes specialized cells that contain stinging structures used for defense & capturing prey. » Found all over a cnidarian’s body but most are on their tentacles » A nematocyst is a stinging structure found in both sea anemones & jellyfish they contain a thin, coiled, harpoon-shaped tubule with a poisonous barb at one end • Gastrovascular cavity sac-like digestive space through which cnidarians stuff prey – Secretes digestive enzymes & absorbs nutrients – Also moves oxygenated water to internal cells Polyp Mouth/anus Tentacle Medusa Gastrovascular cavity Endoderm Body stalk Mesoglea Ectoderm Tentacle Mouth/anus – The four major cnidarian classes are defined by their dominant body form 1) Anthozoans polyp form is dominant, there is no medusa form; include sea anemones & coral Sea anemone (class Anthozoa) 2) Hydrozoans alternate between polyp and medusa; include fire coral, Portuguese Manof-War & hydras Hydra Fire coral Portuguese Man-of-War 3) Scyphozoans medusa form is dominant, very short or no polyp stage; include jellyfish Jellies 4) Cubozoans dominant medusa form; include tropical box jelly fish & sea wasps Sea wasp (class Cubozoa) Box jelly fish (class Cubozoa)