Ch 15 Pseudocoelomate Animals - Gavilan College

Ch 15 Pseudocoelomate Animals - Gavilan College

Ch 11 Pseudocoelomates soo-doe-see-low-mates Acrobeles complexus Pseudocoelomates (Aschelminthes) 7 phyla: Do not molt

Rotifera Acanthocephala Molt Nematoda Nematomorpha Kinoryncha Loricifera Priapulida

Phylogeny Two Hypothesis 1. Phyla related based on anatomy, pseudocoelom, cuticle, muscular pharynx, and adhesive glands. 2. Phyla not related, thus are polyphyletic absence in single unique feature independent

evolution a. similarities result of convergent evolution in similar environments. Pseudocoelomates 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 Plant ectoparasite A. lumbricoides Pseudocoelomates

Common characteristics: 1. First animal to posses a distinct body cavity, but they lack the peritoneal lining and membranes (mesenteries) 2. Pseudocoelom- fluid filled, gelatinous substance, serves for circulation, aids in digestion, acts as hydroskeleton. 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 Pseudocoelom is spacious, fluid-filled and Contains visceral organs No muscular tissue associated with gut tract No membranes suspend organs in

body cavity Common characteristics: 2) Eutely Eutely (thrift) a condition in which the number of cells is constant (i.e. C. elegans = 959 adult) Common characteristics:

3) complete digestive tract (mouth and anus) Found in most other higher animals Common characteristics: 1. Bilateral symmetry 2. Unsegmented, tribploblastic, and

cylindrical in cross section 3. Protonephridia 4. Some cephalization is evident (primitive brain, mouth, sense organs) 5. Dioecious 6. Complete digestive tract (mouth and anus) 7. All have cuticle

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 Pseudocoelomates Organ systems present: Digestive system Excretory system

Nervous system Reproductive system Organ systems absent: Circulatory system Respiratory system Phylum Rotifera

Phylum Rotifera (non Molting) rota= wheel (wave of beating cilia) fera= bearer Freshwater, some marine B/w grains of sand

Ciliated crown (corona) Food, locomotion (movie) Phylum Rotifera Mostly microscopic 1800 species

Many resistant to desiccation dioecious Phylum Rotifera Brain Muscular pharynxmastax

Protonephridia with flame cells Pedal glands Internal Anatomy of a Typical Rotifer Phylum Nematoda The roundworms

Phylum Nematoda (Molt) 16,000 species 500,000 possible Cylindrical body (vermiform) Excretory system renette Mostly dioecious

Only longitudinal muscles Undulate/thrash around (dont crawl) movie Phylum Nematoda Noncellular cuticle with several layers Primary layers of cuticle- cortex, matrix

layer and basal layer Maintains internal hydrostatic pressure Provides mechanical protection Resists digestion by host (in parasitic nematodes) Phylum Nematoda (contd) Found

everywhere Oceans (free living and parasitic) Polar ice Hot springs Soil Some play an important role

in nutrient 5 billion per acre Phylum Nematoda (contd) Eat just about every type of organic

material Rotting substance Living tissue Parasites of nearly all plant and animal species!

Do these questions 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?

Ascaris 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 Life cycle of Ascaris lumbicoides

Figure 11.10 Migrate to Molt Pinworms Most common parasite in US

30% children; 16% adults Large intestine Lay eggs (first-stage larva) in perianal area at night Itch and Spread Fecal oral route Pinworm life cycle

Figure 11.11 Trinchinella spiralis: the Porkworm Figure 11.13 (a) Figure 11.13 (b)

Cyst Larvae in skeletal muscle Filarial Worms Elephantiatis 250 million people (tropics) Lives in lymphatic system Obstruct lymph to cause swelling

Microfilaria of Wuchereria bancrofti Figure 11.15 Wuchereria spp. : Filarial worms Causes Elephantiasis Other parasitic

nematodes Hookworms Dog heartworms Trichinella (causes trichinosis) biomedical research C. elegans

C. elegans Free living nematode 959 cells Development of every cell is known (movie) Genome

sequenced NCBI C. elegans Nobel Prize (2002) Brenner, Sulston and Horvitz Genetic regulation of organ development and

programmed cell death Sydney Brenner - C. elegans since 1963

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