Invertebrate Evolution From Protist to Animials Fungi Opisthokonta

Invertebrate Evolution

From Protist to Animials & Fungi

Opisthokonta = common ancestor of Animals and n Choanoflagellates and fungi n Choanoflagellates – most closely related to n

How it Happened Some relative of Choanofalgellate(Protist? ) mutated to become multicellular instead of colonial n Colonial cells live together but can survive if separated from the colony n Cells of multicellular organisms CAN NOT live on their own n All Metazoans are multicellular n

Proterospongia = Protist & common ancestor to all animals?

Proterospongia: Colonial, Unicellular Protists

Sponge choanocytes (collar cells)

Phylum Porifera Sponges n 3 types of cells n Collar cells (choanocytes) n Amoebocytes n Epidermis cells (protective outer layer of cells) n No tissues n Cells held together by mesohyle (jelly) n Skeleton of spicules & spongin protein n

Intracelluar digestion n n Collar cells take in food by endocytosis Food digested in food vacuoles Some food passed to amoebocytes Amoebocytes carry food around sponge body. (circulaton)

Other Porifera Traits n Asymmetrical = no symmetry n Respiration by diffusion n Excretion by diffusion n Reproduction = male gametes released into water, filtered out of water by another sponge. Female gametes stay in mesohyle until fertilized. Zygote grows into a swimming larva. n Larva settles to ground & becomes sessile adult n

Eumetazoa = Animals with True Tissues

Phylum Cnidaria n n Have stinging cells = cnidocytes Have tentacles n Have myocytes = muscle like cells that contract n 1 st predatory animals n Have Radial symmetry = sit and wait predator n 1 st nervous system = nerve net & eye spots n n

Digestion & Circulation n Have gastrovascular cavity for digestion & circulation n 1 st extra cellular digestion – cells lining GVC secrete digestive enzymes into GVC to digest food Evolutionary advantage = can eat larger food n Cillia lining GVC push digested food particles around the body n n GVC cells branches into all tentacles: comes near all

Respiration & Excretion Respiration by diffusion n Excretion by diffusion n Both are possible since entire body is only a few cell layers away from external water n

Reproduction = complex life cycle Medusa = swimming n Polyp = sessile n Medusa =sexual n Egg & sperm n External fertilizaion n n Polyp = asexual n budding