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

AschelminthsEutely – 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

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Nematode Reproductive Systems

Dioecious

Phylum RotiferaCharacteristics 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 organsProtonephridia with flame cells

• Functions for osmoregulation

Phylum RotiferaReproduction

• 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 KinorhynchaCharacteristics

• < 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 BodyClose up of the proboscisClose up of the proboscis

How the How the proboscis proboscis attaches to attaches to the intestinal the intestinal wall.wall.

All images from:All images from:http://www.biosci.ohio-http://www.biosci.ohio-state.edu/~parasite/state.edu/~parasite/acanthocephala.htmlacanthocephala.html

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

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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 vermicularisSpends 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

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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

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Life Cycle of Necator Americanus

Source: Redrawn From Centers for Disease Control, Atlanta, GA.

Ancylostoma caninum

www.animalplanet.com/s/3336/157?showName=Monsters%20InsideMe&videoEpisode=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

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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

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Source: Redrawn From Centers for Disease Control, Atlanta, GA.11-13

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