Noncoelomate Invertebrates Chapter 33 Invertebrate Phylogeny Revolution Scientists
Noncoelomate Invertebrates Chapter 33
Invertebrate Phylogeny Revolution Scientists generally agree about the taxonomic classification of 36 animal phyla -They do disagree, however, about how these are interrelated Traditional reconstructions lump together phyla that share major features of body plan New reconstructions employ molecular comparisons of r. RNA and other genes 2
Invertebrate Phylogeny Revolution Both old and new phylogenies agree that: -Porifera first separated from Eumetazoa -Among the eumetazoans, Cnidaria and Ctenophora branch out before Bilateria -Bilateria are divided into two groups: protostomes and deuterostomes Modern phylogeny differs radically from traditional phylogeny in construction of the protostome lineage 3
Invertebrate Phylogeny Revolution Traditionally, the branches of animals are based on the nature of the body cavity: -Acoelomates = Have no body cavity -Pseudocoelomates = Have pseudocoel -Coelomates = Have coelom Acoelomates and pseudocoelomates are always protostomes Coelomates are either protostomes or deuterostomes 4
Invertebrate Phylogeny Revolution 5
Invertebrate Phylogeny Revolution Ecdysozoans -Increase in size by molting their external skeletons -Two phyla have been particularly successful -Nematoda: pseudocoelomates -Roundworms -Arthropoda: coelomates -Insects, crustaceans, and others 6
Invertebrate Phylogeny Revolution 7
Parazoans lack tissues, organs and a definite symmetry -However, they have complex multicellularity Sponges, phylum Porifera, are parazoans -Include marine and freshwater species -Larval sponges are free-swimming, but adults are anchored onto submerged objects 8
Parazoa Adult sponges are shaped like a vase Walls of the “vase” have three functional layers 9
Parazoa 1. Inner layer = Specialized flagellate cells called choanocytes, or collar cells 2. Central layer = Gelatinous, protein-rich matrix called the mesohyl 3. Outer layer = Protective epithelium Mesohyl may contain spicules and/or fibers of a tough protein called spongin -These strengthen the body of the sponge 10
Parazoa 11
Parazoa Sponges are “filter-feeders” -Beating of the choanocyte flagella draws water through numerous small pores -Brings in food and oxygen and expels wastes -Small organisms are filtered from the water, which flows through passageways -Eventually exits from the osculum 12
Parazoa Sponge reproduction -Asexual = Fragmentation -Sexual = Egg and sperm -Larval sponges use cilia for swimming -Settle down on a substrate -Transform into adults 13
Eumetazoans are animals with distinct tissues Embryos have distinct layers -Inner endoderm = Forms the gastrodermis -Outer ectoderm = Forms the epidermis and nervous system -Middle mesoderm (Only in bilateral animals) -Forms the muscles 14
Eumetazoans also evolved true body symmetry -Radiata = Exhibit radial symmetry -Phylum Cnidaria -Phylum = Ctenophora -Bilateria = Exhibit radial symmetry -All other animals 15
Phylum Cnidarians are nearly all marine -Bodies have distinct tissues but no organs Cnidarians are diploblastic -Ectoderm (epidermis) and endoderm (gastrodermis) -In between, a layer of gelatinous material (mesoglea) 16
Phylum Cnidarians are carnivores They have two basic body forms -Polyps = Cylindrical and sessile -Medusae = Umbrella-shaped and free-living 17
Fig. 33. 5(left) 18
Phylum Cnidaria 19
Phylum Cnidaria Some cnidarians exist as either medusae or polyps, while others alternate between the two phases Polyps may reproduce sexually or asexually -Asexual reproduction occurs by budding and may produce a new polyp or medusae Medusae reproduce sexually -Form free-swimming larvae called planulae 20
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Phylum Cnidarians have internal extracellular digestion -Digestion begins with extracellular fragmentation in the gastrovascular cavity -This is followed by phagocytosis and intracellular digestion Cnidarians have no circulatory, respiratory or excretory systems 22
Fig. 33. 7 23
Phylum Cnidarians have unique specialized cells on their epidermis called cnidocytes The nematocyst is a special type of cnidocyte -Contains a small but powerful harpoon -Used for food acquisition and defense 24
Phylum Cnidaria 25
Four Classes of Cnidarians Hydrozoa (hydroids) Scyphozoa (jellyfish) Cubozoa (box jellyfish) Anthozoa (corals and sea anemones) 26
The Bilaterian Acoelomates The Bilateria are characterized by bilateral symmetry -Allowed for high levels of specialization Bilaterians are traditionally classified by the condition of their coelom -Acoelomates -Pseudoceolomates -Coelomates 27
Phylum Platyhelminthes The flatworms are soft-bodied animals -Many species are parasitic -Others are free-living Move by ciliated epithelial cells Have developed musculature 28
Phylum Platyhelminthes Flatworms have an incomplete digestive cavity with only one opening -Therefore, they cannot feed continuously Muscular contractions in the pharynx allows food to be ingested and torn into small bits Tapeworms (parasitic flatworms) lack digestive systems -Absorb food directly through body walls 29
Phylum Platyhelminthes Flatworms have an excretory and osmoregulatory system -Network of fine tubules runs through body -Flame cells located on the side branches -Primary function = water balance -Secondary function = excretion Metabolic wastes are excreted into the gut and eliminated through the mouth 30
Phylum Platyhelminthes Flatworms lack a circulatory system -Flattened body shape and highly-branched gut utilize diffusion They have a simple nervous system -Eyespot can distinguish light from dark Most are hermaphroditic -Undergo sexual reproduction -Also have capacity for asexual regeneration 31
Phylum Platyhelminthes 32
Phylum Platyhelminthes 33
Phylum Platyhelminthes -Turbellaria Free-living -Monogenea Parasitic -Trematoda -Cestoda 34
Phylum Platyhelminthes Class Turbellaria -Free-living flatworms -Recently shown to be polyphyletic -Found in freshwater, marine and even terrestrial environments 35
Phylum Platyhelminthes Classes Monogenea and Trematoda -Flukes -Live as ectoparasites or endo-parasites in the bodies of other animals -Attach by suckers, anchors or hooks -Most have a life cycle that involves two or more hosts 36
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Phylum Platyhelminthes Class Cestoda -Tapeworms -Live as parasites within the bodies of other animals -Most species occur in the intestines of vertebrates 38
Phylum Platyhelminthes Class Cestoda -Long flat bodies divided into three zones -Scolex = Attachment organ -Neck = Unsegmented portion -Proglottids = Repetitive sections -Each a complex hermaphroditic unit -Taenia saginata is the beef tapeworm 39
Phylum Platyhelminthes 40
Phylum Platyhelminthes Acoel flatworms were once considered basal members of the phylum Platyhelminthes -Have a primitive nervous system and lack a digestive cavity Are now classified in their own phyla, Acoela 41
Phylum Nemerteans are often called ribbon worms or proboscis worms Are long animals that can stretch to several meters (up to 60 m) 42
Phylum Nemerteans possess a fluid-filled sac, the rhynchocoel: a true coelomic cavity Are the simplest animals with a complete digestive system (mouth and anus) Have a closed circulatory system They are not related to flatworms -Are now classified with other coelomate protostomes in the Lophotrochozoa 43
The Pseudocoelomates Possess a pseudocoel, which is a cavity between the mesoderm and endoderm -Serves as a hydrostatic skeleton, against which the animal’s muscles can work Pseudocoelomates lack a defined circulatory system -Role is performed by fluids that move within the pseudocoel 44
Phylum Nematoda Nematodes are roundworms comprising many species -Found in marine, freshwater and soil habitats Are bilaterally symmetrical and unsegmented 45
Phylum Nematoda Nematodes are covered with a flexible, thick cuticle Are ecdysozoans -Molt cuticle four times Lack specialized respiratory organs and exchange oxygen through their cuticles 46
Phylum Nematoda Mouth is equipped with piercing organs called stylets Food passes through the mouth by the sucking action of the pharynx Undigested material is eliminated through the anus 47
Phylum Nematoda 48
Phylum Nematoda Nematodes usually reproduce sexually -Sexes are separate 49
Phylum Nematoda Many nematodes are active hunters, preying on protists and other small animals Others are parasites of plants Still others live within the bodies of larger animals 50
Phylum Nematoda Nematodes can cause diseases in humans -Trichinella causes trichinosis -Forms cysts in muscles -Ascaris lumbricoides – Intestinal roundworm 51
Phylum Rotifera Rotifers are bilaterally symmetrical unsegmented pseudocoelomates -They have complex internal organs They propel themselves through water by rapidly beating thick cilia at their heads -“Wheel animals” They gather food via a conspicuous organ called the corona 52
Phylum Rotifera 53
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