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Noncoelomate Invertebrates
Chapter 33
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Porifera Parazoa 7000 marine species; 150 freshwater species
Animals lacking tissues (and therefore organs) and a definite symmetry 7000 marine species; 150 freshwater species Among the most abundant animals in the deep ocean Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bryozoa (Ectoprocta) Micrognathozoa Platyhelminthes Ctenophora Cycliophora Brachiopoda Porifera Cnidaria Acoela Rotifera
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Most members lack symmetry Various growth forms
Larval sponges free-swimming Adults remain attached – sessile Cell types Truly multicellular 3 functional layers in “vase”
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3 layers Outer epithelium Mesohyl Choanocytes
Water comes in ostia, exits osculum Mesohyl Middle layer – gelatinous matrix Spicules – needles of calcium carbonate Spongin – reinforcing tough protein fibers Choanocytes Collar cells Flagellated – contributes to water circulation Face internal cavity Engulf and digest food from passing water
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Sponge reproduction Asexual Sexual Fragmentation
Choanocytes transform into sperm Sperm captured and passed to egg cell in mesohyl Development may occur within mother or in open water Larva is planktonic; will settle and transform into adult
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Eumetazoa 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 True body symmetry Radial symmetry Bilateral symmetry
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Phylum Cnidaria Most marine, few fresh water species Diploblastic
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bryozoa (Ectoprocta) Phylum Cnidaria Micrognathozoa Platyhelminthes Ctenophora Cycliophora Brachiopoda Porifera Cnidaria Acoela Rotifera Most marine, few fresh water species Diploblastic Bodies have distinct tissues but no organs No reproductive, circulatory, or excretory systems No concentrated nervous system Latticework of nerve cells Touch, gravity, light receptors
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Cnidarians use nematocysts to capture prey
Secreted within nematocyte Mechanism of discharge unknown Some carry venom
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2 basic body forms Polyps – cylindrical and sessile
Medusa – umbrella-shaped and free-living
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Body plan has single opening leading to gastrovascular cavity
Site of digestion Most gas exchange Waste discharge Formation of gametes in many 2 layers to body wall Epidermis Gastrodermis Mesoglea between layers
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Gastrovascular space also serves as hydrostatic skeleton
Provides a rigid structure against which muscles can operate Gives the animal shape Many polyp species build an exoskeleton of chitin or calcium carbonate around themselves Some build an internal skeleton
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Cnidarian life cycle Some cnidarians occur only as polyps, and others exist only as medusae, but many alternate between these two phases Both phases consist of diploid individuals In general, in species having both polyp and medusa in the life cycle, the medusa forms gametes Sexes separate Gonochorism – individual is either male or female Zygote develops into planktonic planula Metamorphosis into polyp Polyp produces medusae or other polyps asexually
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Major evolutionary innovation in cnidarians is extracellular digestion of food inside the animal
Digestion takes place partly in gastrovascular cavity Cells then engulf fragments by phagocytosis
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4 or 5 classes Anthozoa Sea anemones, most corals, sea fans
Solitary and colonial polyps Symbiotic dinoflagellates (zooxanthellae) photosynthesize and provide nutrients to reef coral Coral reefs economically important
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Cubozoa Hydrozoa Box jellies Strong swimmers, voracious fish predators
Stings may be fatal to humans Hydrozoa Hydroids, Hydra, Portuguese man-of-war Both polyp and medusa stages Only class with freshwater members
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Scyphozoa Staurozoa Jellyfish Medusa more conspicuous and complex
Ring of muscle cells allows for rhythmic contractions for propulsion Staurozoa Star jellies Resembles a medusa in most ways but is attached to the substratum by a sort of stalk that emerges from the side opposite the mouth
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Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Ctenophora Bryozoa (Ectoprocta) Micrognathozoa Platyhelminthes Ctenophora Cycliophora Brachiopoda Porifera Cnidaria Acoela Rotifera Known as comb jellies, sea walnuts, or sea gooseberries 8 rows of comblike plates of fused cilia that beat in a coordinated fashion Many bioluminescent 2 tentacles covered with colloblasts Discharge strong adhesive used to capture prey Phylogenetic position unclear
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The Bilaterian Acoelomates
Characterized by bilateral symmetry Allowed for high levels of specialization Bilaterians are traditionally classified by the condition of their coelom Acoelomates Pseudocoelomates Coelomates Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bryozoa (Ectoprocta) Micrognathozoa Platyhelminthes Ctenophora Cycliophora Brachiopoda Porifera Cnidaria Acoela Rotifera
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Phylum Platyhelminthes
Flatworms are ciliated, soft-bodied animals Bodies are solid aside from an incomplete digestive cavity Many species are parasitic Others are free-living Marine, freshwater, moist terrestrial
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Only one opening to digestive cavity
Muscular contractions in the pharynx allows food to be ingested and torn into small bits Lack circulatory system Diffusion for gas transport Gut functions in digestion and food distribution Some particles digested extracellularly Cells engulf particles by phagocytosis Tapeworms (parasitic flatworms) lack digestive systems – absorb food directly through body walls
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Have an excretory and osmoregulatory system
Network of fine tubules runs through body Flame cells located on the side branches Flagella move water and excretory substances into the tubules and then to pores located between the epidermal cells through which the liquid is expelled Metabolic wastes are excreted into the gut and eliminated through the mouth
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Simple nervous system Reproduction
Anterior cerebral ganglion and nerve cords Eyespot can distinguish light from dark Reproduction Most are hermaphroditic Undergo sexual reproduction Also have capacity for asexual regeneration
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2 major groups Free-living Turbellaria Parasitic Neodermata
Probably not monophyletic Dugesia – common planarian in bio labs Parasitic Neodermata Trematoda – flukes Attach within host body by suckers, anchors, or hooks Life cycle may have 2 or more hosts Clonorchis sinensis, oriental liver fluke Cercomeromorpha – tapeworms
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One of most important trematodes to human health are blood flukes Schistosoma
Afflict 5% of world’s population About 800,000 people die each year from schistosomiasis or bilharzia Fertilized egg must break through the wall of the blood vessels in intestine or the urinary bladder to get out
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Cercomeromorpha – tapeworms
Adult hangs onto inner wall of host intestine using scolex
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Most of tapeworm body is proglottids
Complete hermaphroditic unit, containing both male and female reproductive organs Formed continuously Beef tapeworm, Taenia saginata Frequent human parasite From eating uninspected rare beef
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Phylum Acoelomorpha Acoel flatworms were once considered basal members of the phylum Platyhelminthes Have a primitive nervous system and lack a digestive cavity Based on molecular evidence, similarities are convergent
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Phylum Cycliophora Discovery reported in 1995
Striking circular mouth surrounded by a ring of cilia Anatomy and life cycle are very unusual Live on the mouthparts of claw lobsters on both sides of the North Atlantic
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Pseudocoelomates Pseudocoelom – cavity that lies between tissues derived from the mesoderm and those derived from the endoderm Pseudocoelomic fluid performs the functions carried out by a circulatory system in most coelomate animals Not monophyletic Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bryozoa (Ectoprocta) Platyhelminthes Cycliophora Brachiopoda Kinorhyncha Onychophora Chaetognatha Echinodermata Rotifera Annelida Mollusca Nemertea Loricifera Nematoda Tardigrada Arthropoda Chordata
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Phylum Nematoda Vinegar eels, eelworms, and other roundworms
Members of this phylum are found everywhere – abundant and diverse Marine, freshwater, parasites, free-living
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Bilaterally symmetrical and unsegmented
Covered by a flexible, thick cuticle that is molted as they grow Digestive system well developed Stylets – piercing organs near mouth Pharynx – creates sucking action Anus
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Sexual reproduction Eutely Most gonochoric
Sexual dimorphism – male smaller with hooked end Internal fertilization Indirect development – egg, larva, adult Eutely Adults consist of a fixed number of cells Caenorhabditis elegans has only 959 cells Important in genetic and developmental studies
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Lifestyles Many are active hunters, preying on protists and other small animals Others are parasites of plants Still others live within the bodies of larger animals Largest known nematode, which can attain a length of 9 m, parasitizes the placenta of sperm whales
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About 50 species cause human diseases Hookworms
Common in southern U.S. Produce anemia Trichinella causes trichinosis Forms cysts in muscles Infection from eating undercooked meat
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Pinworms, Enterobius vermicularis
Infects 30% of children in U.S. Causes itching of the anus Ascaris lumbricoides – intestinal roundworm Infects 1 in 6 worldwide Adult female can be 30 cm long Rare in areas with modern plumbing Serious tropical nematode diseases Filariasis Elephantiasis
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Phylum Rotifera Bilaterally symmetrical, unsegmented pseudocoelomates
Highly developed internal organs Corona – “wheel animals” Conspicuous ring of cilia at anterior end Used for locomotion and sweeping food into the mouth
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