The Pseudocoelomate Body Plan Chapter 11

Aschelminths –Any of the seven phyla grouped together –Rotifera, Kinorhyncha, Nematoda, Nematomorpha, Acanthocephala, Loricitera, and Priapulida

Aschelminths

Pseudocoelomate Body Plan Lack mesentary, organs lie free Often fluid-filled or contain a gelantinous substance Most have complete tubular digestive tract from mouth to anus which allows for mechanical breakdown of food, digestion, absorption and feces formation

Aschelminths Most are microscopic (some grow to over a meter) Bilaterally symmetrical Unsegmented Triploblastic Cylindrical in cross section Most are dioecious (reproductive organs are in separate animals)

Aschelminths Most are microscopic (some grow to over a meter) Most are free-living, some are parasitic Bilaterally symmetrical Unsegmented Triploblastic Cylindrical in cross section Most are dioecious (reproductive organs are in separate animals) Cuticle present: may bear spines or scales and is useful for protection and taxonomic identification Molting or ecdysis shed their cuticle

Aschelminths Eutely – Same number of cells for each animal and for each given organ Ex. Caenorhabditis elegans (a type of nematode) has 959 cells Every worm has 80 cells in their pharnyx Page 176

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nematode Reproductive Systems

Dioecious

Phylum Rotifera Characteristics  Corona – ciliated organ around the head used for locomotion and food gathering  0.1 to 3 mm in length  Most are freshwater (less than 10% marine)

Phylum Rotifera Characteristics Cont… Usually solitary, free swimming animals although there are a few colonial members Posterior end with toes and adhesive glands Parthogenesis common, males reduced in this phylum

Phylum Rotifera External features Epidermally secreted cuticle used for protection –Lorica – thickened cuticle that makes an encasement used for protection and support –Epidermis is synctial –Head has a mouth, brain, sensory organs –Foot has 1-2 toes »Foot has pedal glands

Phylum Rotifera Body parts –Head (Anterior) »Corona »Mouth »Buccal field –Trunk »Middle –Foot »Toes »Adhesive glands

Phylum Rotifera Digestion Mastax jaw that grinds food Other organs Protonephridia with flame cells Functions for osmoregulation

Phylum Rotifera Reproduction Some perform sexual reproduction (several use parthogenesis) Class Seisonida –2 Species –Marine –Haploid eggs that must be fertilized –Males & females develop equally Class Bdelloidea –All females are parthenogenic –Diploid eggs that produce females –No males present Class Monogononta –Amictic eggs – diploid eggs –Mictic eggs – haploid eggs, can become amitic –Sporadic small sized males

Phylum Kinorhyncha Characteristics < 1mm in length Marine environments- burrow in mud & sand with snouts 150 species Dioecious Feed on diatom & algae and organic matter

Phylum Kinorhyncha Composed of 13 or 14 zonites –Definite units called zonites –Zonite 1 can retract into zonite 2 –Spines line most zonites »Pair of lateral spines and one dorsal spine –Protonephridia in Zonite 11 –Brain and ventral nerve cord with a ganglion in each zonite

Loricifera Discovered in 1974 Dioecious Have a large brain Little else is known about them.

Priapulida Only 9 species All marine worms Found in colder water Predaceous Fossils date back to Middle Cambrian.

Enterobius vermicularis Pin worm 50% of children in US Spread –Fecal oral route –Airborne Spends its entire life in humans. Adult worms are in the large intestine in humans. The female migrates to the anus to deposit her eggs. This causes the itching that is the most common symptom. Eggs are then ingested by the host or another human (commonly transmitted in young children who are not very hygienic). Sticky tape method

Phylum Acanthocephala Spiny headed worm 2-host parasites –Must have invertebrate host Spiny protruding proboscis Both circular and longitudinal muscles

Nutrition Nutrition by diffusion Proboscis attaches to host intestine Cause extensive damage to the intestinal walls Some forms cause serious discomfort and ill-health to domestic livestock

Characteristics Spiny or thorny-headed All are intestinal parasites of vertebrates Common in various fishes (mostly freshwater) birds (chickens and turkeys) mammals and a few reptiles and amphibians. Typically cylindrical and small (few mm - cm) Constant number of cells, which is species specific

The Acanthocephalan Body Close up of the proboscis How the proboscis attaches to the intestinal wall. All images from: state.edu/~parasite/acanthocephala.htm l

Phylum Nematomorpha Commonly called horsehair worms or Gordian worms Up to 1m long, but very slender animals (1-3mm) Free-living as adults Often find adults in very clean streams Juveniles are parasitic in arthropods (beetles, cockroach)

Nematodes Found everywhere –Soil –Oceans –Polar ice –Hot springs Parasites of nearly all plant and animal species!

Phylum Nematode Microscopic to several meters long Feed on organic matter –Rotting substances to living tissues of other invertebrates, vertebrates and plant.

Phylum Nematode 12,000 species –500,000 possible Most abundant animal (some 5 billion may be in an acre of fertile garden soil) Cylindrical body Only longitudinal muscles Noncellular cuticle with several layers

Phylum Nematode Some have lips, some have spines or teeth on those lips Sensory organs –Amphids – chemoreceptors along the cuticle –Phasmids - chemoreceptors near the anus –Ocelli – eyespots found in aquatic nematodes

Ascaris lumbricoides Roundworm of man 1.2 billion people –Many in southeast US Females lay 200,000 eggs a day Unsanitary habits contaminate ground Moves by thrashing back and forth

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Source: Redrawn From Centers for Disease Control, Atlanta, GA. Life Cycle of Ascaris Lumbricoides

Nematode-Caused Diseases Roundworms - more than ½ the world's humans Hookworms Trichinosis (Porkworm) Pinworm infestations - extremely common parasite in the United States Filariasis (elephantiasis) Onchocerciasis (river blindness)

Ascarid Worms (common roundworm) - lives in intestine - eggs are passed out in the feces Most roundworms infect dogs, but occasionally they find their way into human hosts

Enterobius vermicularis Pinworms 50% of children in US Spread –Fecal oral route –airborne

Enterobius vermicularis Spends its entire life in humans. Adult worms are in the large intestine in humans. The female migrates to the anus to deposit her eggs. This causes the itching that is the most common symptom. Eggs are then ingested by the host or another human

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Life Cycle of Enterobius Vermicularis Source: Redrawn From Centers for Disease Control, Atlanta, GA.

Hookworms Anterior end hooks Feed on blood Cause anemia Necator americanus Ancylostoma duodenale

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Life Cycle of Necator Americanus Source: Redrawn From Centers for Disease Control, Atlanta, GA.

Ancylostoma caninum Episode=Worms%20Crawling%20Under%20My%20Skin

Cutaneous Larval Migrans Hookworms from dogs and cats

Trichinella spiralis Trichina worm: causes trichinosis cysts within the muscles are consumed (undercooked food) worm grows in intestine forms cysts in the muscles of the new host symptom: terrible pain in muscles Diagnosis is by muscle biopsy

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Source: (a) Redrawn From Centers for Disease Control, Atlanta, GA. (b) Photo © Steve Miller Life Cycle of Trichinella Spiralis Acquired by ingestion of contaminated pork containing the encysted larva. The larvae mature into adults in the human digestive tract. They sexually reproduce and give birth to live nematodes that migrate throughout the body and become encysted in muscles and other tissue. Infects pigs, bears, dogs, cats, rats & humans

Dirofilaria immitis Dog heart worm

Wuchereria bancrofti Filarial worms- mostly in tropical regions Infect the lymph vessels which are responsible for returning fluid to the circulatory system Obstruct lymph to cause swelling –Elephantiasis

-- usually transmitted by mosquitoes -- causes elephantiasis

Elephantiasis

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Source: Redrawn From Centers for Disease Control, Atlanta, GA Life Cycle of Wucheria spp.

Loa loa Eye worm Can cause encephalitis

Dracunculus medinesis Fiery serpent

Necator americanus – hookworm. Adults live in the small intestine and eggs are excreted with feces. They hatch in the soil and the larva can enter a new host by penetrating the skin. The go to the blood and the lungs where they are swallowed and get to the small intestine to mature into an adult. Diagnosis is by finding eggs in the feces. To prevent infection – wear shoes