Animal body plans and Phyla Porifera, Cnidaria, Ctenophora Lecture 4 Reading: Miller Chapter 9 How Did Animals Get Here? A Few Theories… Today We Will Examine What is a Porifera? What is a Cinidaria? What is a Ctenophore? Colonial hypothesis: dividing cells of an early protist stayed together Origins of multicellularity Syncytial hypothesis: formation of a plasma membrane in the cytosplasm of an early syncytial protist Phylum Porifera (sponges) • Primarily marine animals • 9000 species worldwide Phylum Porifera • Characteristics: • Loosely organized cells but lack true tissues • Lack symmetry • No circulation or nervous system • Lack cephalization (no head) • Most reproduce sexually and asexually Spicules: provide structural support Incurrent Canal Porifera body plans Figure 9.6 Sponge Body Forms in more detail. Ascon: simplest, thin walls, tube shaped Sycon: thicker, folded body wall Leucon: largest, most complex • Complex sponges have increased surface area for choanocytes which results in filtering large volumes of water. • Pinacocytes: Line the outer surface, mildly contractile Cell Types, Body Wall and Skeletons • Porocytes: specialized pinacocytes that help regulate water circulation Cell Types Body Wall, and Skeletons • Mesohyl (middle spongy layer) • Mesenchyme cells : these cells move about in the middle layer and • 1. perform reproductive functions • 2. secrete skeletal elements • 3. transport and store food • 4. form contractile rings around the opening Cell Types, Body Walls, and Skeletons • Choanocytes • Collar cells that are flagellated • Create water currents through the sponge Cell Types, Body Walls, and Skeletons • The skeleton of sponges may be formed in one of two ways: • 1. Spongin- fibrous protein made of collagen. These fibers give the sponge its shape and keep it from collapsing spongin • 2. Spicules – made of calcium carbonate or silica Water Current and Body Forms Class Demospongiae Examples of porifera Class Hexactinellida Class Calcarea • Freshwater Demospongiae Porifera • Feed on algae, protists, bacteria and suspended organic matter • A single sponge can filter 20 liters of water a day (10 gallons) • No lungs- gas exchange via diffusion • Most have only 1 sex but do not self-fertilize Ecology • Reduce turbidity of coastal waters • A few are carnivorous • Many have photosynthesizing endosymbionts (photosynthetic organisms that live within sponge) • Food for turtles, fishes, ducks, crayfish, sponge flies • Habitat for symbionts: e.g., shrimp, feed off particles that collect on sponge • Human uses: bathing, washing, cosmetics Sponge Reproduction Pause and Reflect • What is a sponge? • Why are they important? • Why are they an important link between unicellular and multicellular animals? • How do they reproduce? Phylum Cnidaria • Cnidarians (jellies, anemones, corals, hydra) • Diploblastic (2 germ layers) • Radial symmetry • Not cephalized (no head) • Simple nervous system (nerve net) • Specialized cells, called cnidocytes, used in defense, feeding, and attachment Tissues • Hydrostatic skeleton: Water confined within grastrovascular cavity creates hydrostatic compartment • Provide support and aid body movement Figure 9.8 Body wall of a cnidarian (Hydra). Cnidae • Zoologists have described nearly 30 types • Some cnidae contain unarmed tubes that wrap around prey • Some cnidae help anchor the animal • Nematocysts used in food gathering and defense • Spines have hollow tips and deliver paralyzing toxins • Animals may have 6+ kinds of cnidae in one individual Nerves and Movement Cnidarian Body Forms Alternation of Generations • Many cnidarians possess two body forms in their life histories • Polyp – asexual and sessile • Cylindrical body • Mouth surrounded by food gathering tentacles • Budding produces miniature medusae • Medusa – dioecious and free swimming • Shaped like inverted bowl • Tentacles hang from free margins • Swims with gentle pulsations Reproduction: Alternation of Generations Cnidarian Life Cycle Classification Pause and Reflect • What is a Cnidarian • How are they different from sponges • Why are they important • How many Classes of Cnidarians exist? Hydrozoa Obelia Hydra Gonionemus Characteristics: *External Nematocysts *Epidermal gametes *Acellular mesoglea Portugese Man O’War Man of War Staurozoa • *Goblet-Shaped • *8 sets of • tentacles • *Limited dispersal • *lack medusa stage Scyphozoa: “True Jellyfish” • *Mesoglea with amoeboid cells • *Cnidocytes also in gastrovascular Cavity • * Dominant stage in life history is medusa Anthozoa: Corals and Anemones Marine, lack medusae •Has a pharynx •Divided gastrovascular Cavity •* Anthozoan life cycle…. Cubozoa: “Cube Jellyfish” •*Polyp stage very small or unknown •*Medusa cube-shaped •*Tentacles at corners •*Some dangerous! Cellular mesoglea and true muscle cells suggest that members may be triploblastic. Locomotion by bands of fused cilia are called comb rows Phylum Ctenophora: comb jellies Tentacles contain adhesive cells called colloblasts that capture prey Biradial symmetry Gelatinous, cellular mesoglea Monoecious with gastrodermal gonads External fertilization leads to flattened larval stage. Figure 9.22 Phylum Ctenophora. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education Phylum Ctenophora Sea Walnuts/Comb Jellies Coral Reefs Local and Global Pressures Threaten Coral Reefs Questions?