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

Architectural patterns of animals Architectural patterns of animals. These basic body plans have been variously modivied during evolutoinary descent to fit aimals to a great variety of habitats. Ectoderm is shown in gray, mesoderm in red, and endoderm in yellow

Pseudocoelomates 9 phyla: Nematoda Rotifera Gastrotrichia Nematomorpha Acanthocephala Loricifera Kinoryncha Priapulida Entoprocta

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: Pseudocoelom Eutely complete digestive tract (mouth and anus)

Common characteristics: 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: 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: Eutely Body composed of constant number of somatic cells (or nuclei) in adults

Common characteristics: complete digestive tract (mouth and anus) Most other higher animals http://www.wormatlas.org/handbook/alimentary/alimentary2.htm

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?

Pseudocoelomates Organ systems present: Organ systems absent: Digestive system Excretory system Nervous system Reproductive system Organ systems absent: Circulatory system Respiratory system All figures from http://wormatlas.org

Phylum Nematoda The roundworms

Phylum Nematoda 12,000 species Cylindrical body Mostly dioecious 500,000 possible Cylindrical body Mostly dioecious Only longitudinal muscles Undulate/thrash around (don’t crawl) movie

Phylum Nematoda Noncellular cuticle with several layers Maintains internal hydrostatic pressure Provides mechanical protection Resists digestion by host (in parasitic nematodes)

Phylum Nematoda (cont’d) Found everywhere Oceans Polar ice Hot springs soil

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!

Ascaris lumbricoides Human parasite 1.2 billion people 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

Pinworms Most common parasite in US 30% children; 16% adults Large intestine Lay eggs in anus at night Spread Fecal oral route Up to 1.2 cm

Filarial Worms “Elephantiatis” 250 million people (tropics) Lives in lymphatic system Obstruct lymph to cause swelling Microfilaria of Wuchereria bancrofti

Other parasitic nematodes Hookworms Dog heartworms Trichinella (causes trichinosis)

biomedical research C. elegans

C. elegans Free living nematode 959 cells Genome sequenced Development of every cell is known (movie) Genome sequenced NCBI 1090 generated. Exactly 131 programmed death

C. elegans Nobel Prize (2002) Brenner, Sulston and Horvitz “Genetic regulation of organ development and programmed cell death” Sydney Brenner - C. elegans since 1963 Using the nematode C. elegans this year's Nobel Laureates have demonstrated how organ development and programmed cell death are genetically regulated. They have identified key genes regulating programmed cell death and demonstrated that corresponding genes exist also in higher animals, including man. The figure schematically illustrates the cell lineage (top left) and the programmed cell death (below) in C. elegans. The fertilized egg cell undergoes a series of cell divisions leading to cell differentiation and cell specialization, eventually producing the adult organism (top right). In C. elegans, all cell divisions and differentiations are invariant, i.e. identical from individual to individual, which made it possible to construct a cell lineage for all cell divisions. During development, 1090 cells are generated, but precisely 131 of these cells are eliminated by programmed cell death. This results in an adult nematode (the hermaphrodite), composed of 959 somatic cells. http://www.nobel.se/medicine/laureates/2002/press.html

Phylum Rotifera

Phylum Rotifera Ciliated crown (corona) rota= wheel fera= bearer (movie) http://www.microscopyu.com/galleries/dxm1200/images/collothecalarge.jpg

Phylum Rotifera Mostly microscopic 1800 species Many resistant to desiccation dioecious http://micro.magnet.fsu.edu/primer/techniques/phasegallery/images/rotifer.jpg

Phylum Rotifera Aquatic (mostly freshwater) Protonephridia with flame cells Internal Anatomy of a Typical Rotifer