INVERTEBRATES

INVERTEBRATES

1. The Evolution of Multicelluarity

   • Different types of protist could symbiotically form a composite multicellular organism  e.g.lichens by fungal and algal partners. Asexual division producs of a single individual protist could remain together after fission, and multicellularity arise via an intermediate colonial stage.  A multinucleae protist could evolve internal membrane partitions around each of its nuceli, confining its sphere of operation to a certain region of of the body and thereby become internally compartmented.
   • [Image: http://i140.photobucket.com/albums/r3/Dalapix/a.jpg] [Image: http://i140.photobucket.com/albums/r3/Dalapix/b.jpg] [Image: http://i140.photobucket.com/albums/r3/Dalapix/c.jpg]

2. Sponges

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   • multicellular
   • Sponges are suspension feeders. They capture food particles suspended in the water
   • 4 types of cells. *Choanocyes. *Amoebocytes. *Porocytes. * Epidermal cells
     • Choanocytes. (aka Collar Cells). These cells are mophologically and functionally identical to the free living protist choanoflagellates. These cells engulf bacteria and food particles by phagocytosis. The movement of the flagellum draws water throught its collar of finger like projections. Food particles are trapped in the mucus that coats the projections.  Amoebocytes. Named for their use of pesuedopodia. These cells move through the mesophyll and take up food from surrounding water and choanocytes, digest it and carry food to other cells. They also manufacture tough skeletal fibres within the mesohyl (sharp spicules of CaCO3 or flexible spongin. Porocytes. Porocytes are doughnut shaped cells that span the body wall.These cells have pores allowng water to enter the spongocoel. Epidermal Cells.Tight packed cells that make up the outer layer.
   • Basal animals that lack true tissues.
   • Body consist of 2 layers of cells, separated by a gelatinous layer (mesohyl)
   • Most are hermaphrodites, almost all exhibit sequential hermaphroditism.
     • Sponge gametes arise from choanocytes or amoebocytes.  Eggs reside in the mesohyl. Sperm are carried out of the sponge by the water current. Fertilisation occurs in the mesohyl. zygotes develop into flagellated, swimming larvae that disperse from the parent sponge. After settling on a suitable substrate, a larva develops into a sessile adult.
   • Antibiotic synthesis. The compount cribostatin isolated from sponges can kill penicillin resistant strains of the bacterium Streptococcus

3. Cnidaria

   • Eumetazoa. Animals with true tissues
   • Sessile and motile forms
   • Hydras. Jellies. Corals.
   • Exhibit the relatively simple, diploblastic radial bodyplanthat existed 560mya
   • 2 variations of the bodyplan. Polyps and medusae
     • Polyps. Cylindrical forms that adhere to the substrate by the aboral end of their body and extend their tentacles waiting for prey. E.g Hydras, Sea An
     • Medusae.flattened mouth-down polyp. Moves freely by passive drifting and contraction of bell-shaped body. Tentacles dangle from oral surface.
   • Carnivores. Use tentacles to capture prey and push the food into the gastrovascular cavity where digestion begins.
   • Cnidocytes. Unique cells only to cnidaria. Function in defence and prey capture
     • Cnidocytes contain cnidae (from the GREEK nettle), capsule like organelles that are capable of exploding outward. Specialised cnidae called nematocysts contain a stinging thread that can penetrate the body wall of the cnidarians prey.
   • Contractile tissues and nerves are present in their simplest form. Bundles of microfilaments arranged into contractile fibres
     • Cells of the epidermis and gastrodermis have bundles of microfilaments arranged into contractile fibres.  The gastovascular cavity acts as a hydrostatic skeleton against which the contractile cells can work.  When a cnidarian closes it mouth, the volume of the cavity is fixed, and contaction of the selected cells causes the animal to change shape.  Movements are coodinated by a nerve net.
   • The phylum cnidaria is divided into 4 major clades. Hydrozoa, Scyphozoa, Cubozoa and Anthozoa
   • Body wall has 2 layers of cells- an outer layer of epidermis and inner layer of gastrodermis

4. Lophotrochozoans

5. Ecdysozoans

6. Deuterostomia