Invertebrates Noncoelomate

2 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 rRNA and other genes

3 Invertebrate Phylogeny Revolution Both old and new phylogenies agree that: -Porifera belongs to protozoa -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

4 Invertebrate Phylogeny Revolution

5 Modern protostome phylogeny distinguishes between two major clades that have evolved independently: -Spiralians: Grow by adding mass to an existing body -Ecdysozoans: Increase in size by molting their external skeletons

6 Invertebrate Phylogeny Revolution Spiralians -Grow by adding mass to an existing body -Two main groups -Lophotrochozoa: mostly coelomates -Include the phyla Brachiopoda, Mollusca and Annelida -Platyzoa: mostly acoelomates -Include the phyla Platyhelminthes, and Micrognathozoa

7 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

8 Invertebrate Phylogeny Revolution

10 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 Parazoa

11 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

12 Sponge reproduction -Asexual = Fragmentation -Sexual = Egg and sperm -Larval sponges use cilia for swimming -Settle down on a substrate -Transform into adults Parazoa

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 Eumetazoa

14 Eumetazoans also evolved true body symmetry -Radiata = Exhibit radial symmetry -Phylum Cnidaria -Phylum = Ctenophora -Bilateria = Exhibit bilateral symmetry -All other animals Eumetazoa

15 Invertebrate Phylogeny Revolution

16 Cnidarians are carnivores They have two basic body forms -Polyps = Cylindrical and sessile -Medusae = Umbrella-shaped and free-living Phylum Cnidaria 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

18 Hydrozoa (hydroids) Four Classes of Cnidarians Scyphozoa (jellyfish) Cubozoa (box jellyfish)Anthozoa (corals and sea anemones)

19 A small phylum whose members are known as comb jellies, sea walnuts or sea gooseberries Phylum Ctenophora Structurally more complex than cnidarians Capture prey with a colloblast -Contains strong adhesive material

20 Ctenophores propel themselves through water with eight rows of fused cilia They are triploblastic -Have true muscles cells derived from the mesoderm Their mode of symmetry is not strictly radial as in cnidarians

21 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 The Bilaterian Acoelomates

22 Invertebrate Phylogeny Revolution

23 The flatworms are soft-bodied animals -Many species are parasitic -Others are free-living Phylum Platyhelminthes Move by ciliated epithelial cells Have developed musculature

24 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 Phylum Platyhelminthes

25 Flatworms have been traditionally grouped into four major classes -Turbellaria -Monogenea -Trematoda -Cestoda New studies group all three parasitic classes into a single group, Neodermata Free-living Parasitic

26 Class Turbellaria -Free-living flatworms -Recently shown to be polyphyletic -Found in freshwater, marine and even terrestrial environments 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

27 Clonorchis sinensis: Oriental liver fluke -Complex life cycle -Miracidium – Ciliated stage in egg -Rediae – Nonciliated larvae produced within sporocyst -Cercaria – Tadpole-like larval stage -Metacercaria – Adult stage produced within cysts

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29 Other important flukes are the blood flukes of the genus Schistosoma -Three species cause the disease schistosomiasis, or bilharzia -Worms coat themselves with host’s own antigens -Thus, are immunologically invisible

30 Class Cestoda -Tapeworms -Live as parasites within the bodies of other animals -Most species occur in the intestines of vertebrates

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32 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

33 Nemerteans are often called ribbon worms or proboscis worms Phylum Nemertea Are long animals that can stretch to several meters

34 Nematodes are roundworms comprising many species -Found in marine, freshwater and soil habitats Are bilaterally symmetrical and unsegmented Phylum Nematoda

35 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

36 Nematodes are roundworms comprising many species -Found in marine, freshwater and soil habitats Are bilaterally symmetrical and unsegmented

37 Nematodes are covered with a flexible, thick cuticle Are ecdysozoans -Molt cuticle four times Lack specialized respiratory organs and exchange oxygen through their cuticles

38 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

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40 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