Biology Lecture: Animal Diversity Part 1

BIOLOGY II LECTURE 8 ANIMAL DIVERSITY PART 1 ANIMAL DIVERSITY PART 1 Chapter 33 Section 33.1 Animal Body Plans – pp. 739-745 (including Case 7 Biology-Inspired Design: Using Nature to Solve Problems) Chapter 42 - Biology: How Life Works, Morris et al. Chapter 42 Section 42.1 (pp. 945 to 952) ANI...

BIOLOGY II LECTURE 8 ANIMAL DIVERSITY PART 1 ANIMAL DIVERSITY PART 1 Chapter 33 Section 33.1 Animal Body Plans – pp. 739-745 (including Case 7 Biology-Inspired Design: Using Nature to Solve Problems) Chapter 42 - Biology: How Life Works, Morris et al. Chapter 42 Section 42.1 (pp. 945 to 952) ANIMAL DIVERSITY PART 1 Objectives: Animal Body Plans (required reading) Sponges Radial Animals (Cnidarians and Ctenophorans) Placozoans WHAT IS AN ANIMAL? Animal kingdom is very diverse: 1.3 million living species of animals identified so far Huge diversity; many body plans Basic definition: Animals are multicellular, heterotrophic eukaryotes with a distinctive mode of early development Important to note that 95% of all known animal species are invertebrates (no backbone) 4 ANIMAL PHYLOGENY Simple phylogenetic tree of animals: – animals are closely related to choanoflagellates, but differ from them since animals: are multicellular form a gastrula during early development synthesize collagen Sponges diverged from other animals early Cnidarians diverged later from animals whose descendants have well-defined and complex organs 5 PHYLOGENY OF BILATERIAN ANIMALS 6 PHYLUM PORIFERA - SPONGES Sponges are sessile, have porous body and choanocytes Freshwater and marine Suspension feeders – capture food particles suspended in the water that passes through their body – filtering very important in many aspects of sponge biology Sponge filtering video 7 PHYLUM PORIFERA - SPONGES Similarity between choanocytes and cells of choanoflagellates supports molecular evidence suggesting animals evolved from choanoflagellate-like ancestor Germ layers of sponges are loose groupings of cells not really tissues g lack true tissues Sponges lack true nerves or muscles individual cells can sense and react to changes in the environment No symmetry Basal animals 8 PHYLUM PORIFERA - SPONGES Mesohyl Epidermis Pores (ostia) Spicules – Calcium carbonate or silica – Some with no spicules, only protein Spongocoel Osculum Choanocytes Amoebocytes 9  PHYLUM PORIFERA - SPONGES Nutrition via intracellular digestion Some sponges have symbiotic organisms that help them gain additional nutrition There is coordination of flagellar beating of choanocytes Gas exchange via diffusion Simple reproduction Gametes develop in mesohyl; Fertilization  sperm released; fuse with eggs in mesohyl of another sponge Some sponges produce toxins and antibiotics Cribrostatin Can kill antibiotic resistant strains of Streptococcus Ongoing research reveal the possibility of other compounds that may be anti-cancer agents 10 PHYLUM CNIDARIA All animals except sponges belong to the clade Eumetazoa (true tissues and symmetry) Phylum Cnidaria is one of the oldest groups in this clade Are sister group to Bilateria Cnidarians have: radial symmetry a gastrovascular cavity cnidocytes 11 Phylum Cnidaria Very diverse group including jellies, corals, and hydras – Floating forms (medusa) – Sessile forms (polyp) – Diploblastic Synapomorphies: – Radial symmetry – Mouth surrounded by tentacles armed with stinging cells (cnidocytes) 12  PHYLUM CNIDARIA Closed internal gastric cavity = gastrovascular cavity site of extracellular/intracellular digestion and excretion a cavity enclosing digestive enzymes allows digestion of large food items. A single opening functions as both mouth and anus 13  PHYLUM CNIDARIA Body wall with two layers of cells: Outer eipdermis (from ectoderm) Inner gastrodermis (from endoderm) cells of the epidermis and gastrodermis with bundles of microfilaments arranged into contractile fibers (not true muscle, but muscle-like cells) Mesoglea – acellular layer 14 PHYLUM CNIDARIA Carnivorous use tentacles to capture prey The tentacles are armed with cnidocytes with nematocysts function in defense and capture of prey Video of nematocysts discharging Noncentralized nerve net - simple sensory receptors; radially distributed 15  FOUR MAJOR CLASSES OF CNIDARIANS Scyphozoans Medusa predominant stage Hydrozoans of life cycle Alternate between polyp and Most live among medusa plankton (jellies) Hydra – polyp only Cubozoans Anthozoans Box jellies and sea wasps Sea anemones and Box-shaped medusa with corals complex eyes (fringe) Occur only as Tropical with toxic polyps cnidocytes Corals – hard external skeleton of calcium carbonate 16  ? PHYLUM CTENOPHORA (COMB-JELLIES) Resemble cnidarians in body plan; thought to be close relatives but are more complex Important differences between cnidarians and comb-jellies: Cilia Simple flow-through gut with mouth and anal pore This unique combination of traits makes placement on the tree of life difficult 17 PHYLUM PLACOZOA ? Very simple organisms - no specialized tissues and few differentiated cell types: Upper and lower epithelia Interior fluid crisscrossed by a network of multinucleate fiber cells Cilia on cell surfaces to allow movement Genome contains many genes for transcription factors and signaling molecules that are present in cnidarians and bilaterian animals. 18 PHYLOGENETIC TREE WITH PLACOZOANS AND CTENOPHORES ADDED DNA sequences Where support Placozoans Ctenophorans fit is as sister group to a problem! Cnidaria and Bilaterians Traditional hypothesis Alternative hypothesis Cnidaria and Bilateria as sister groups supported by molecular, anatomical and embryological data 19 WHERE DO THE CTENOPHORA FIT? Traditional hypothesis Alternative hypothesis Traditionally DNA sequence Branch off, with Cnidaria comparisons show and Bilaterians as sister evidence that group to sponges Supported by molecular ctenophores are sister data group to all other animals! 20