Ch 33.6, 42.1, 42.5, 44.3 Pseudocoelomates “soo-doe-see-low-mates”

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Acrobeles complexus

Ch 33.6, 42.1, 42.5, 44.3 Ch 33.6, 42.1, 42.5, 44.3 Pseudocoelomates Pseudocoelomates “soo-

doe-see-low-mates”

PseudocoelomatesPseudocoelomates• 9 phyla:

– Nematoda– Rotifera– Gastrotrichia– Nematomorpha– Acanthocephala– Loricifera– Kinoryncha– Priapulida– Entoprocta

PseudocoelomatesPseudocoelomates

Plant ectoparasite

A. lumbricoides

• A heterogeneous group: – Size: microscopic several

meters– some are exclusively marine;

some (e.g., nematodes) live in a variety of habitats, esp. soil); and some are exclusively parasitic

PseudocoelomatesPseudocoelomates• Common characteristics:

1. Pseudocoelom2. Eutely3. complete digestive tract (mouth and

Common characteristics: 1) Pseudocoelom

• body cavity (pseudocoelom/ pseudocoel)

• a space b/w gut and mesodermal components of body wall

• Body cavity is not lined with a mesodermal sheet – Does not cover inner surface of body wall

Common characteristics: 1) Pseudocoelom

• No muscular tissue associated with gut tract

• No membranes suspend organs in body cavity

• Pseudocoelom is spacious, fluid-filled– Contains visceral organs– Forms hydrostatic skeleton

Evolutionary advantages of pseudocoel:– Greater freedom of movement– Space for development and

differentiation of organ systems (ie. digestive, excretory)•differentiation: process by which cells

become different, specialized– Simple means of circulation/distribution

of materials throughout body– Storage place for waste products to be

discharged to outside– Hydrostatic skeleton

•Fluid enclosed by muscular wall support

Common characteristics: 2) Eutely

• Body composed of constant number of somatic cells (or nuclei) in adults

http://www.wormatlas.org/handbook/alimentary/alimentary2.htm

Common characteristics: 3) complete digestive tract (mouth and

anus)• Most other higher animals

Do these questions Do these questions now…now…

• What type of germ layer lines the pseudocoelom in nematode embryos?

• What organ systems are present/absent in pseudocoelomates

• What are the advantages of having a pseudocoelom vs. no coelom?

• Organ systems present:– Digestive system– Excretory system– Nervous system– Reproductive system

• Organ systems absent:– Circulatory system– Respiratory system

PseudocoelomatesPseudocoelomates

Phylum NematodaPhylum Nematoda

The roundworms

Phylum NematodaPhylum Nematoda• 12,000 species

– 500,000 possible• Cylindrical body• Mostly dioecious• Only longitudinal

muscles– Undulate/thrash

around (don’t crawl) movie

Phylum NematodaPhylum Nematoda• Noncellular cuticle with several layers

– Maintains internal hydrostatic pressure– Provides mechanical protection– Resists digestion by host (in parasitic

nematodes)

Phylum Nematoda Phylum Nematoda (cont’d)(cont’d)

• Found everywhere– Oceans– Polar ice– Hot springs– soil

5 billion per acre

Phylum Nematoda Phylum Nematoda (cont’d)(cont’d)

• Eat just about every type of organic material– Rotting

substance– Living tissue

• Parasites of nearly all plant and animal species!

Ascaris lumbricoidesAscaris lumbricoides• Human parasite

– Up to 30cm long• 1.2 billion people

– Many in southeast US• Females lay 200,000

eggs a day• Unsanitary habits

contaminate ground– Ingest eggs– Hatch bury into

veins lungs pharynx

– Swallowed intestine

PinwormsPinworms

• Most common parasite in US

• 30% children; 16% adults• Large intestine• Lay eggs in anus at night• Spread

– Fecal oral route

Filarial WormsFilarial Worms• “Elephantiatis”• 250 million people

(tropics)• Lives in lymphatic system• Obstruct lymph to cause

swelling

Microfilaria of Wuchereria bancrofti

Other parasitic Other parasitic nematodesnematodes

• Hookworms• Dog heartworms• Trichinella

(causes trichinosis)

• biomedical research– C. elegans

C. elegansC. elegans

• Free living nematode

• 959 cells– Development of

every cell is known (movie)

• Genome sequenced– NCBI

http://www.nobel.se/medicine/laureates/2002/press.html

Sydney Brenner- C. elegans since 1963

• C. elegans • Nobel Prize (2002)

Brenner, Sulston and Horvitz– “Genetic regulation of

organ development and programmed cell death”

Phylum RotiferaPhylum Rotifera

http://www.microscopyu.com/galleries/dxm1200/images/collothecalarge.jpg

– rota= wheel– fera= bearer

• Ciliated crown (corona)– (movie)

http://micro.magnet.fsu.edu/primer/techniques/phasegallery/images/rotifer.jpg

• Mostly microscopic• 1800 species• Many resistant to

desiccation• dioecious

Internal Anatomy of a Typical Rotifer

• Aquatic (mostly freshwater)– Protonephridia with flame

Ch 33.6, 42.1, 42.5, 44.3 Pseudocoelomates “soo-doe-see-low-mates”

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