Unit 4 - Phylums Platyhelminthes and Nematoda Flatworms and Roundworms

Phylum Platyhelminthes Largest group of acoelomate (no body cavity) worms Flatworms with middle tissue layer- mesoderm Tissues organized into organs Bilaterally symmetrical and flat Cells lie close to exterior enabling efficient diffusion of oxygen and carbon dioxide Highly branched gastrovascular cavity runs close to all tissues giving cells ready access to food No respiratory or circulatory systems

Coelom – Body Cavity The coelom usually performs multiple functions, including one or more of the following: Provides room for organ development Surfaces for diffusion of gases, nutrients, and wastes Storage Hydrostatic support

Phylum Platyhelmithes Flatworms Liver Flukes, Planaria and tapeworms Marine flatworms Characteristics: Ribbon-like bodies Bilateral symmetry Branched digestive system No skeleton Asexual (fission); Hermaphrodites (sexual) Free movement Skin breathing

Phylum Platyhelminthes Class Turbellaria Most free-living; marine Dugesia- Freshwater planarians Digestion- Nutrients absorbed by intestinal wall and waste goes out through mouth Muscular pharynx comes out of central mouth to feed

Phylum Platyhelminthes Reproduction- Mostly asexual by attaching posterior end to stationary object and pulling into two Hermaphrodites can reproduce sexually Nervous system: Brain, two nerve cords, and light-sensitive eye spots Water balance- Water continually enters by osmosis Flame cells with cilia draw water to the outside

Phylum Platyhelminthes Marine flatworm

Phylum Platyhelminthes

Planarian

Phylum Platyhelminthes Many parasitic Endoparasite- internal Ectoparasite- external Class Cestoidea Subclass Eucestoda- Parasitic flatworms (tapeworms) Suckers and hooks on scolex (head) attach to walls of intestines and food absorbed from host’s intestines directly through the tapeworm’s skin

Phylum Platyhelminthes String of rectangular body sections (proglottids) Each proglottid is a reproductive unit Added continually through life May grow up to 12 m (40 ft.) long

Phylum Platyhelminthes Most occur in vertebrates Dozen types in humans Taenia saginata- Beef tapeworm Live in cow muscles in cysts High temp. kills larvae Subclass Cestodaria Body not subdidvided into proglottids Larvae in crustaceans; adults in fish

Scolex Examples

Phylum Platyhelmithes

Proglottid – reproductive structure

Phylum Platyhelminthes Largest flatworm class, Trematoda Parasitic worms called flukes Endoparasites or ectoparasites Subclass Aspidogastrea (Aspidobothrea)- Endoparasite of mollusks Subclass Digenea- Endoparasites of vertebrates

Phylum Platyhelminthes Tegument- thick protective covering prevents them from being digested Take nourishment directly from hosts Use suckers to attach and the muscular pharynx to suck nourishment from host’s body fluids

Phylum Platyhelminthes Complex life cycles involve more than one host Ex: Schistosoma- Responsible for schistosomiasis From contaminated water Larvae bore into host skin into blood vessels of intestines Block vessels causing bleeding and damage to liver Snail is intermediate host

Phylum Platyhelminthes Class Monogenea – Monogenetic flukes One life cycle in one host Mostly ectoparasites on vertebrates

Phylum Platyhelminthes Liver fluke

Phylum Nematoda Roundworms- have a pseudocoelom (body cavity between endoderm & mesoderm) Fluid movement serves as circulatory and gas exchange system Fluid also distributes nutrients to cells from digestive system

Phylum Nematoda Long, cylindrical bodies Majority microscopic and free-living One-way digestive system Thick, flexible epidermis protects and gives shape Layer of muscle underneath pulls at epidermis and pseudocoelem for whip-like movement

Phylum Nematoda Roundworms Ascaris, Trichinella and hookworms Characteristics: Flattened bodies Bilateral symmetry Many are parasites Fluid-filled body cavity called a pseudocoelem Digestive tube No skeleton Sexual reproduction (Internal fertilization) Sperm is amoeboid Free movement Skin breathing

Phylum Nematoda Class Secernentea (Phasmidea)- Phasmids (sensory structures) in tail Ascaris, Enterobius, Rhabditis, Turbutrix, Necator, and Wuchereria Class Adenophorea (Aphasmidia)- No phasmids Dioctophyme, Trichinella, Trichuris 50 species are parasitic Plant parasites feed on living plant cells in all parts of plant, causing wilting and withering 14 species affect humans Ex: Enterobius (pinworms), Ascaris lumbricoides, Trichinella spiralis, Necator (hookworms)

Phylum Nematoda Trichinella infects pigs and causes trichinosis (serious disease caused by eating undercooked pork) Necator live in warm, moist soils of the tropics Hookworm larvae enter bloodstream through soles of feet

Phylum Nematoda Ascaris Carried in human waste After ingestion, eggs hatch into larvae in intestines Larvae bore through blood vessels, enter blood stream and then lungs (causes respiratory distress) Larvae may enter gallbladder or pancreas causing blockages Return to intestines to mature and mate May grow up to 1 ft. in length

Phylum Nematoda Ascaris Trichinella

Trichinosis Trichinella spiralis is found in pork Trichinosis is a disease caused by the Trichinella worm. Eggs hatch in the host’s gut Symptoms: Diarrhea Fever Muscle pain Death

Common Parasitic Roundworms Hookworms attach to the inside of the digestive tract Often found in pets Pinworms- most common Heartworms- transmitted to dogs by mosquitos Filarial worms- live in blood where they block blood vessels or lymph vessels causing severe swelling (Elephantitis) Guinea worm- Ingested with contaminated water Cause dracunculiasis Only found when exiting skin Found in Africa, India and Pakistan