3 Worm Phyla (long, thin bodied animals) All eumatazoans (have true tissues) All have bilateral symmetry Develop a coelom → body cavity 1. Phylum Platyhelminthes (flatworms) 2. Phylum Nematoda (roundworms) 3. Phylum Annelida (segmented worms)

Nematodes The Roundworms

Nematodes (roundworms) 12,000+ species Size ranges from less than 1 mm to more than 1 meter Among the most widespread of all animals Some are parasitic (both plants and animals) Some are free-living in most aquatic and soil habitats Triploblastic Psuedoceolomates First group of organisms to have 2 openings to digestive tract Round cross section Body covered in cuticle

Nematode ecology Make up 15% of the biomass at the bottom of freshwater lakes A handful of soil will contain 1000’s of microscopic, free living nematodes. Nematodes help enrich soil Nematodes can stop all their life activities and go to sleep when conditions are unfavorable (cryptobiosis)

Nematode Anatomy Cuticle – smooth flexible covering over the body to prevent fluid loss and provide protection Epidermis – skin cells that lie under the cuticle Hypodermis – specialized ectoderm cells that secrete material that makes the cuticle Psuedocoelom – fluid filled body cavity containing intestines and reproductive organs Muscle fibers – under hypodermis. derived from mesoderm. contract to create whip-like wriggle movement of wormwriggle

Nematode Digestion Complete gut (endoderm): Mouth – located at the anterior end and takes in food Stylet – mouth spear Pharynx – pumps food into the intestine (throat) Intestine – a long tube that digests food and absorbs nutrients Excretory gland – removes nitrogen from nutrients (ammonia) Excretory pore/canal – lets waste from excretory gland out of the body Anus – expels wastes/undigested food from intestines

Nematoda Reproduction Essentially reproductive machines… Reproductive organs Ovaries – make eggs Testes – make sperm Specialized amoeboid sperm (no flagella) Reproductive site Spicule – injects sperm Gonopore – site of egg expulsion

Reproduction Most species have both male and female organisms. Males inject sperm into females Fertilization is internal and fertilized eggs are then released from the female’s gonopore. The eggs hatch into larva with will eventually develop into a worm. Some are hermaphroditic A few species can reproduce asexually by parthenogenesis → embryos form from unfertilized egg cells in the adult

Life Cycle of Nematodes Eggs hatch 1 st larval stage Eats bacteria, molts 2 nd larval stage Free-living or intermediate host, molts 3 rd larval stage Infective stage, finds host Adult Parasitic – feeds in host, reproduces Eutely – every individual of a given species has the exact same number of cells. Once this cell number is achieved, cells grow to increase animals size instead of the number of cells multiplying

Life Cycle

Nervous, Respiratory and Circulatory systems Nerve ring - Nerve cords – receive sensory information and coordinate movement (dorsal & ventral cord as well as lateral cords) Associated with sensory cells: Touch (anterior & posterior) Chemical sensors (anterior) Light sensitive Ocelli (simple eyes) No true respiratory/circulatory systems, instead… Nematodes rely on diffusion to obtain oxygen from their environment and to have materials/nutrients travel through their body. “Breathe” across the entire surface of their body Nematodes must have a wet film on their body in order to have diffusion in/out of body.

PARASITES Trichinella- parasitic nematode species found in pigs. Eggs are transmitted in meat (eaten by people) - cooking pork kills eggs Eggs hatch, larva are carried to muscles where they burrow, painful Trichonosis- disease caused by Trichinella

Examples Hookworms- eggs are passed through human waste products, hatch into to larvae in soil, burrow in feet Common in warm climates where there is not good sanitation One species of Nematode is a parasite of the Sperm Whale and grows up to 13 meters long.