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Simple Animals Sponges and Placozoa the Twig of the Tree That Is the Animals the Tour Begins

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Simple Animals Sponges and Placozoa the Twig of the Tree That Is the Animals the Tour Begins Animal Kingdom Simple animals Sponges and placozoa Tom Hartman Asymmetry www.tuatara9.co.uk Animal form and function 1 Module 111121 2 The twig of the tree that is the animals Animals All other animals Animals Sponges Choanoflagellates Choanoflagellates Fungi Fungi 3 4 All other animals Animals (bilateralia) Radiata Sponges Choanoflagellates Fungi The tour begins 5 6 1 Animal Kingdom The Phylum Quirky phyla • In the standard Linnean system (and taxonomic systems • There are 39 animal phyla (+/- 10!) based on it), a Phylum is the taxonomic category between Kingdom and Class. • The Micrognathozoa were • A phylum is a major ranking of organisms, defined discovered in 2000 (1 species)in according to the most basic body-parts shared by that springs in Greenland. group. But we must include the creatures and their • Xenoturbellida removed from the common ancestor. molluscs and moved to the – Chordata (animals with a notochord - vertebrates and others), – Arthropoda (animals with a jointed exoskeleton) dueterostomes when DNA – Mollusca (animals with a shell-secreting mantle), evidence was discounted due to – Angiosperma (flowering plants), and so on. what it had eaten! – A number of traditional Phyla - e.g. Protozoa, possibly Arthropoda - • Cycliophora discovered on the are probably invalid (polyphyletic). lips of lobsters in 1995. 7 8 The Class Our journey • In the Linnean system (and taxonomic systems Kingdom Group Phylum based on it), a Class is the taxonomic category Porifera between Phylum and Order. Placozoa • A class is a major group of organisms, e.g. Cnidaria Mammalia, Gastropoda, Insecta, etc that Parazoa Ctenophora contains a large number of different Radiata Platyhelminthes sublineages, but have shared characteristics in Animalia Protostome Rotifera common e.g. Annelida – warm-blooded, fur, mammary glands in female (apart Mollusca from some bats) in the case of mammals, Brachiopoda Deuterosome – six legs and three body parts in the case of Insects, Nematoda etc. Tartigrada – Reptilia is polyphyletic if it does not include the birds Onychophora (and mammals). Arthropoda 9 Plus 26 other phyla 10 Features of being an animal Animal body plans so far. • Nutrition Radial symmetry Bilateral symmetry • Being large (though some are not) No true tissues • Being multicellular Choanoflagellates • Cells specialization (and unique ones) • Tissues (including unique ones) • Development • Symmetry Multicellular • Layers of cells Single cell Stalk 11 12 2 Animal Kingdom Animals can be characterized by “body plans” Points of Agreement • Sponges are: • All animals share a common ancestor – Multicellular (metazoa) (RTK, cell structures, genes). – Heterotrophic • Sponges are basal animals. – Have some specialised cells. • Parazoa (Parazoana) are a clade without • They do not have tissues. true tissues. • No desmosomes. • The eumetazoa is a clade of animals with • They do not undergo gastrulation true tissues. • As a branch of the animal line they are sometimes called the parazoa. 13 14 Animal body plans so far. Sponges No true tissues Radial symmetry Bilateral symmetry Parazoa Choanoflagellates True tissues Eumetazoa Multicellular Single cell Stalk 15 16 Phylum Porifera Types of sponges Sponges • Chalky: secrete calcium carbonate to add • Sponge bodies are diverse: hard textures. – encrusting sheets • Glassy: secrete silica based elements for – volcano-shaped mounds protection. – tubes (1mm-1m) • Mixed: the largest group of sponges – upright sheets (demosponges) can have silica parts, • Two layers of cells spongin fibres and/or calcium carbonate. separated by a jelly layer. 17 18 3 Animal Kingdom Useful word derivations Parts of a sponge • ‘Coel’ – from koilos . Greek for •All poriferans have a canal system. cavity. •Water enters through • Blastocoel pores called ostia , • Spongeocoel flows through canals to a spacious chamber • Coel om called a spongocoel , • Acoel omate and finally exits through large openings called oscula ... Cells and matrix 19 20 Levels of complexity Levels of complexity • The simplest form consists of •The vast majority of a single tube two cell layers sponges are thick. Poriferans with this type of architecture are organized in a more necessarily very small due to complex way, the surface area to volume ‘leucon’ condition, constraints. with folds upon folds, • In order for a sponge to resulting in a series of attain greater size, the flagellated chambers sponge wall must be folded in on itself. A simple folding of connected by canals. the wall yields a sponge body with ‘sycon’ organization. All drawn to look beautifully symmetrical! 21 22 Cell Types in a Sponge Deconstructing sponges • In 1907 H V Wilson mashed up a sponge Outer Epithelial Cells and pushed it through a sieve. • The cells crawled about and the reassembled themselves precisely. • He then did it with two different species. Porocytes • He called the experiment a failure when allow water into sponge they separated and did not make a hybrid. Choanocytes (collar cells) circulate water, filter food 23 particles 24 4 Animal Kingdom The cells of a sponge (contd) Spicule Choanocyte Choanoflagellate Outside Archaeocyte Sclerocyte Mesenchyme Pinacocyte Choanocyte Porocyte Pore/osteum Single cell Water current Canal Stalk Flagellum 25 Collar 26 The choanocyte cell. flagellum Sponges are fantastic pumps • 20,000 x its own volume every 24 hours. • Some sponges trap 90% of all bacteria. Each is microvillus . • Can change water composition… Cylindrical shape of microvillus increases S/V. 27 28 Spicules 29 30 5 Animal Kingdom Reproduction Spicules • Asexual. Can regenerate from fragments. • Why do sponges look good to eat? • Many are hermaphrodite. – Low or no motility • Choanocytes may form the – Highly visible reproductive cells (i.e. de- differentiate) – Nutritious cell layers • Sperm are released into the • BUT water and taken up in the same way as food. • Most biomass is armour or spongin • Larval stage settles away from – Spikes parent. • Larval stages invert as their – Rubbery texture cilia form inside the blastula. – Velcro = carnivorous sponges 31 32 The moving sponge Small phylum: Placozoa • Body form of a flat plate that can move in any direction and form pseudopodia. • No symmetry. • Multicellular body plan consisting of: – an upper cell layer (most with a flagellum). – a fluid filled cavity with a network of fibre cells that contract in a coordinated way to change shape. – A lower layer of flagellated cells and glandular cells that secrete enzymes to break down their prey. Leaving the sponges 33 34 The position of the Placozoa is unresolved! • Asexual reproduction by fission or budding. • Sperm and eggs do appear but their development has not been observed. • Smallest genome in animal kingdom. • Mistaken for a motile larvae of a sponge or a cnidarian until 1971. 35 36 6 Animal Kingdom The first branches Radial symmetry Cnidaria All others Sponges Placozoa two cell layers Bilateral symmetry Radial symmetry Three cell layers Two cell layers No true tissues True tissues Parazoa Eumetazoa Multicellular 37 38 7.
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