Chapter 15 Pseudocoelomate Animals Kingdom: Phylum: Class: Order:

I. Intro A. General Characteristics of pseudocoelomates a. bilateral, unsegmented, triploblastic, complete gut (tube within a tube), lack circulatory and respiratory systems, dioecious, b. 2 cavities gut cavity + pseudocoel formed from blastocoel lack true coelom (peritoneal cavity), not lined w/ peritoneum c. body wall (epidermis)/dermis/muscles surrounding pseudocoel

B. Evolutionary Advantages of Pseudocoelom a. ↑ freedom of movement b. space for development (niche)/differentiation of digestive/reproductive/excretory systems c. storage area for wastes d. hydrostatic skeleton

C. Structure of a Nematode Identify symmetry?????

II. Phylum Nematoda (Nemata): A. Form/Function a. Muscles –longitudinal (no circular), beneath hypodermis run in 4 bands, marked by 4 hypodermal cords Hydrostatic pressure each muscle cells has contractile fibrillar portion (spindle) + noncontractile sarcoplasmic portion (cell body) –sarcoplasmic extends into pseudocoel, stores glycogen –What is glycogen???? –fibrillar is striated w/actin/myosin –See next slide: actin/myosin

P. Nematoda (Nemata): Form/Function b. Feeding/digestion –parasitic/predatory –mouth → pharynx → non-muscular intestine → rectum → anus –food sucked into pharynx muscles contract, lumen expands –intestine is 1 cell thick –food moves posteriorly as new food enters and body moves –defecation occurs via opening anus + allowing pseudocoelomic pressure to expel waste

P. Nematoda (Nemata): Form/Function c. How do Nematodes get their energy?? –Anaerobic energy metabolism –Glycolysis??? d. Nervous/sensory system –2 nerve cords, ventral nerve cords –sensory papillae at head/tail –amphids = pair of sensory organs on head lead into a deep cuticular pit w/ modified cilia Dendrites

Phylum Nematoda (Nemata): Form/Function d. Reproduction –most dioecious w/ ♂ smaller than ♀ –♂ has copulatory spicules to hold ♀ vulva open against hydrostatic pressure –internal fertilization –eggs stored in uterus until deposited

III. Phylum Nematoda Examples Common human parasites covered in class –Ascaris (large roundworms) –Pinworms –Hookworm –Porkworm –Filarial worms –Guinea worm

1 st Nematode Parasite: Ascaris Large roundworm of humans (Ascaris lumbricoides) –up to 64% of people in some areas of SE US –+1.2 Billion affected worldwide –infection rates highest in children –♂ more heavily infected than ♀ –♀ lays 200,000 eggs/day –eggs pass via host’s feces –embryos develop into infective juveniles in 2 wks killed by direct sunlight/↑ temp. resistant to dessication/↓ O 2 –eggs remain viable long after fecal matter disappears

P. Nematoda: Ascaris continued… –infection via ingestion of eggs (finger/uncooked veggies) –juveniles hatch, burrow through intestinal wall to veins/lymph carried through ♥ to lungs break into alveoli and carried up trachea/pharynx coughed up/swallowed pass to stomach –mature in intestine after 2 months feed on intestinal contents may block/perforate intestines emerge from anus/throat enter eustachian tubes/middle ear Roundworm in dogs/cats –similar life cycle as human roundworm –juveniles migrate to uterus of pregnant dogs puppies infected

2 nd Nematode Parasite: Necator Hookworms (Necator americanus) –9–11 mm –hook-like curve on anterior end –dioecious –large plates in mouth cuts into intestinal mucosa then suck host’s blood suck more than they digest (anemia) –eggs pass in feces –infective juveniles burrow through skin to blood –travel in blood to lungs –coughed up and swallowed –mature in the intestine –Secrete anticoagulant

Life Cycle of Hookworm

3 rd Nematode Parasite: Trichina Trichina worm (Trichinella spiralis) –tiny –+ 2.4% of US –trichinosis (potentially lethal) –adults burrow into intestinal mucosa –♀ directly produce juvenile worms –juveniles penetrate blood vessels/circulate throughout body to all tissues (live yrs) –penetrate skeletal muscle redirecting gene expression of the musculature so it loses its striations becomes a nurse cell to the parasite –encyst in muscle –excyst when poorly cooked meat containing encysted juveniles is eaten –infect humans/hogs/rats/cats/dogs

4 th Nematode Parasite: Enterobius Pinworms (Enterobius vermicularis) –most common nematode parasite in the US 30% all children, 16% all adults –causes little disease –+ 12 mm –adults live in large intestine/cecum –♀ migrate to anal region at night/lay eggs (Scotch Tape Method) itching scratching contaminates hands and bedclothes –eggs develop/become infective w/i 6 hrs at body temp. –ingested, hatch in duodenum, mature in large intestine –haploid ♂ from unfertilized eggs –diploid ♀ come from fertilized eggs (haplodiploidy)

5th Nematode Parasite: Filarial Worms Filarial worms –8 sp. infect humans, 250 million people infected –some live in lymphatic system –cause inflammation/blockage of lymphatics –♀ release live young (microfilariae) into blood/lymph –mosquitoes ingest microfilariae –worms develop to infective stage –move into mosquito bite wound when it feeds –Elephantiasis caused by repeated exposure swelling/growth of connective tissue –dog heartworm (Dirofilaria immitis) most common U.S. filarial worm transmitted by mosquitoes

Incidence in the United States

Side note Guinea Worms