Acrobeles complexus

Ch 11 Pseudocoelomates Ch 11 Pseudocoelomates “soo-doe-see-low-mates”

PseudocoelomatesPseudocoelomates• 9 phyla:

– Rotifera- do not molt (Lophotrochozoan)

– Acanthocephala

– Nematoda molt (Ecdysozoan)– Nematomorpha

– Kinoryncha

– Loricifera

– Priapulida

– Gastrotrichia

– 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

pinworms

PseudocoelomatesPseudocoelomates

• Common characteristics: 1. Pseudocoelom

2. Eutely

3. complete digestive tract (mouth and anus)

Acanthocephalans and nematomorphs do not have a complete digestive tract

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

Phylum RotiferaPhylum Rotifera

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

– rota= wheel

– fera= bearer

• Ciliated crown (corona)– (movie)

Phylum RotiferaPhylum Rotifera

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

• Mostly microscopic

• 1800 species

• Many resistant to desiccation

• dioecious

Phylum RotiferaPhylum Rotifera

Internal Anatomy of a Typical Rotifer

• Aquatic (mostly freshwater)– Protonephridia with flame

cells