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

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 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

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  support

Organ systems present: –Digestive system –Excretory system –Nervous system –Reproductive system Organ systems absent: –Circulatory system –Respiratory system Pseudocoelomates

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)(movie)

Phylum Rotifera Mostly microscopic 1800 species Many resistant to desiccation dioecious

Phylum Rotifera Internal Anatomy of a Typical Rotifer Brain Muscular pharynx- mastax Protonephridia with flame cells Pedal glands

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 (don’t crawl) moviemovie

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 (cont’d) Found everywhere –Oceans (free living and parasitic) –Polar ice –Hot springs –Soil Some play an important role in nutrient recycling

5 billion per acre

Phylum Nematoda (cont’d) 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 –Swallowed  intestine

Figure Life cycle of Ascaris lumbicoides Molt Migrate to

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 –Larval molt four times in Small Intestines and migrate to large Intestines

Figure Pinworm life cycle

Figure (a) Trinchinella spiralis: the Porkworm

Figure (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 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)(movie) Genome sequenced –NCBINCBI

Sydney Brenner - C. elegans since 1963 C. elegans –Nobel Prize (2002) Brenner, Sulston and Horvitz –“Genetic regulation of organ development and programmed cell death”

Nematode-destroying fungi