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Published byJonathan Stanley Modified over 9 years ago
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How do the acoelomates fit in? Porifera unknown common ancestor Cnidaria triploblastic organ level of organization Platyhelminthes protonephridia cephalization Ladder-like nervous system Nemertea proboscis Complete digestive system Closed circ. system acoelomate
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How do the Pseudocoelomates fit in? unknown common ancestor Porifera Cnidaria PlatyhelminthesNemertea the pseudocoelomates Nematoda Rotifera
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Pseudocoelomates There are 9 different phyla that are classified as pseudocoelomates. We are only covering 2 phyla: NematodaRotifera
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Pseudocoelomate Characteristics Organ level of organization Tissues are organized to for organs which are used to accomplish physiological functions Triploblastic 3 Germ Layers endoderm mesoderm ectoderm 3 Tissue Layers gastrodermis mesoderm epidermis
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Pseudocoelomate Characteristics “false” body cavity ectoderm mesoderm endoderm Gut pseudocoelom the pseudocoelom is lined by mesoderm on ONE side only
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Pseudocoelomate Characteristics the pseudocoelom ectoderm is a closed, fluid filled cavity contains digestive, excretory, and reproductive structures the fluid within acts as a circulatory system the fluid within acts as a hydrostatic skeleton against which the muscles work
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Pseudocoelomate Characteristics with anterior and posterior ends Bilateral Symmetry Cephalization concentration of sensory organs in the head of the animal
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Pseudocoelomate Characteristics complete (they have an anus!) some regional specialization Digestive System Circulation System no system (or organs) performed by the pseudocoelom fluid
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Pseudocoelomate Characteristics each individual of a species has the same # of cells growth occurs by cells getting bigger rather than dividing Eutely
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Phylum Nematoda the roundworms
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Physiology Life Style –Free-living –parasitic Digestion –complete system (have an anus) –some regional specialization (e.g. an esophagus)
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Physiology Skeletal system -fluid in pseudocoelom acts as a hydrostatic skeleton Cuticle –covers body (secreted by epidermis + composed mostly of collagen) – functions as a primitive external skeleton
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Physiology Movement –longitudinal muscles ONLY (results in “whiplike” motion) –No external/internal cilia even sperm don’t have flagella http://www.devgen.com/devpage/largeimage/wild.html
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Physiology Nervous system -cephalization, cerebral ganglia -dorsal and ventral nerve cords Circulatory system –No system (no organs) –performed by fluid in pseudocoelom Excretion –Renette glands
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Physiology Reproduction Sexual –usually dioecious –often the sexes are sexually dimorphic (males and females look different) Males often have a spicule at the end of their tail used to insert their sperm into the female
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Physiology Reproduction Sexual –usually dioecious –often the sexes are sexually dimorphic –internal fertilization –males have ameboid sperm
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Ecology There are >12,000 species that are found in almost all habitats (marine, freshwater, underground, inside plants and animals, etc…). They are also incredibly abundant. For example: a m² of soil may contain >4 million nematodes a decomposing apple may contain >90,000 nematodes of a single species
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Ecology Many nematodes are important parasites of both plants and animals. parasite of soybean plants parasite of tomato plants
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Parasites Eye worm (Loa loa): transmitted by fly bites larvae go through bloodstream adults live in subcutaneous tissue
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Parasites Intestinal roundworm (Ascaris): transmitted by contaminated food adults live in small intestine it’s estimated that 20% of world’s population is infected (~1.3 billion people) this intestine was completely blocked
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Parasites Guinea worm (Dracunculus medinensis): transmitted by infected copepods in drinking water larvae move into the body cavity female adult migrates to the subcutaneous tissue, causes an ulcer/blister, and releases eggs through hole when host comes in contact with water
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Parasites Guinea worm (Dracunculus medinensis): traditionally removed by winding the worm around a matchstick over the course of several days this may be the basis for the Caduceus symbol used in the medical field
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Parasites Trichinella spiralis: causes Trichinosis transmitted by eating undercooked pork juveniles encyst within host muscle cells juvenile Host muscle cell
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Parasites Heartworms (Dinofilaria immitis):
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Ecology The study of the model nematode C. elegans has resulted in important discoveries in genetics and development.
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Phylum Rotifera the rotifers
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The “wheel” animals
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Physiology Feeding –have a “crown” of cilia called a corona –the corona creates a current to bring food into the mouth
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Physiology Feeding –have a specialized feeding structure called the: mastax-trophi complex a modified muscular pharynx modified jaws within the mastax
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Looking down into the corona….
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Physiology Some of the trophi (jaws):
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Physiology Life Style –Free-living Digestion –complete system (have an anus) –some regional specialization (e.g. mastax-trophi complex)
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Physiology Skeletal system -fluid in pseudocoelom acts as a hydrostatic skeleton Movement –the corona –pedal glands (produce adhesive), as well as foot and toe (spurs) for attachment to substrate
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Physiology Nervous system -cephalization, cerebral ganglia -dorsal and ventral nerve cords Circulatory system –no system (no organs) –performed by fluid in pseudocoelom Excretion –protonephridia and flame cells –cloacal bladder (collects wastes)
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Physiology Reproduction Sexual -complex life cycle with different types of eggs -usually dioecious but in some groups, males are absent (parthenogenesis) -Parthenogenesis: unisexual reproduction where females produce offspring from unfertilized eggs (virgin birth)
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Physiology 2 types of eggs: amictic & mictic Amictic eggs diploid (mitotically produced) can’t be fertilized develop into diploid, amictic females
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Physiology Mictic eggs haploid (meiotically produced) produced after some sort of environmental stimulus (eg. high density, change in temperature) if unfertilized, develop into haploid males if fertilized, secrete a thick, protective shell until the environment is favorable again, after which they develop into diploid, amictic females
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There are ~1500 species. Although they are found mainly in freshwater habitats, there are a few marine rotifer species and a couple of species are even found in mosses! Because of the reduced role of males in reproduction, most males are incapable of feeding and do not even have a digestive tract (they are just there for sperm delivery!). Males have never been recorded in Bdelloid rotifers. This means they haven’t had sex in millions of years! Ecology
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Here are some of the other pseudocoelomate phyla
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Loricifera Priapulida Kinorhyncha Nematomorpha
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Acanthocephala Entoprocta Gastrotricha
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How do the Pseudocoelomates fit in? unknown common ancestor Porifera Cnidaria PlatyhelminthesNemertea Nematoda Rotifera triploblastic organ level of organization mastax-trophi corona pseudocoelom no cilia longitudinal muscles only complete digestive system
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