Unit 3 Platyhelminthes and Nematoda Phylum Platyhelminthes flat

Unit 3 Platyhelminthes and Nematoda

Phylum Platyhelminthes (flat + worm) Over 20, 000 species. Habitat: Aquatic free-living OR parasitic

Flatworms-Platyhelminthes Least complex worm No body cavity (acoelomate) No respiratory system No circulatory system ◦ All cells close to environment

Form & Function: Triploblastic (three germ layers) 1. Ectoderm-Nervous, sensory, skin 2. Mesoderm-Connective tissue, reproductive, excretory, muscle. 3. Endoderm- Gut/respiratory lining, digestive.

Regeneration is the ability to “re-grow” lost body parts. This is possible because the organism has the ability to form a blastema, which is an accumulation of undifferentiated cells, at the site of the wound called Neoblasts (adult stem cells) These undifferentiated cells will eventually differentiate into the missing parts.

Flatworms Three Classes ◦ Turbellerians (Planarian) ◦ Cestoda (Tapeworms) ◦ Trematoda (Flukes)

Class Turbellaria (commotion + like) Turbulence of cilia gives name • Free living • Freshwater or marine • Bottom dwelling • Osmosis Problem – flame cells pump out water (remember contractile vacuole) • Over 3000 species (Planaria n)

Turbellarians Symmetry –Bilateral Structure ◦ shovel head ◦ flat body

Rhabdites: rodlike cells that form protective mucus layer Adhesive glands: secretes chemical that sticks animal to substrate

A) Nervous system B) Reproductive system C) Digestive system Flame Cell

NERVOUS SYSTEM Mass of nerve cells [ganglia] form a simple brain Ladder-like arrangement throughout body Head sensitive to touch, smell, and taste Two eyespots sensitive to light

Auricle Ocelli

REPRODUCTION Reproduction Asexual If cut into pieces – each piece will grow into new organisms Split themselves apart Sexual Produce both male and female sex cells (hermaphodidic) Cannot fertilize itself Lay eggs

When conditions are favorable, the organism will attach its tail-end to the ground and pull forward with its head-end until it tears itself in half. Each end will then regenerate its missing half. This is a form of asexual reproduction called fission. The two “new” planaria are clones of each other, both possessing identical genes.

COOL! Planaria Regeneration An injury divided the head of this planarian in half. The two halves regenerated their lost parts. Eventually, the planarian will split lengthwise into two new planarians.

Digestive system: Turbellaria use their pharynx on ventral side to capture food. One way digestive system so waste exits pharynx too . Feed on small inverts. Also scavengers, and herbivores. Partial external digestion so food is small enough to ingest.

Digestion Excretion

The Monsters Inside Me

Class Trematoda (perforated + form) Common name Flukes- Parasitic to vertebrates Habitat: Most of life cycle spent in host organism Genus: Fasciola (liver fluke)

Class Trematoda Parasitic flukes a) Liver flukes b) Schistomomes / intestinal flukes that suck blood c) use snails as an intermediate host sucker

FLUKE – flat/parasitic Monoecious / hermaphroditic uterus Class Trematoda ovary testis

Nutrition: Feed on the host’s cells. Tegument: exterior layer of fluke that aids in transport of nutrients & protects from host organisms digestive enzymes.

suckers SEM image

Intestinal Schistosomiasis 16 yr. Old boy Abdomen accumulates fluida body immune response to eggs embedded in tissues

Definitive host Schistosomiasis Intermediate host

Class Cestodea (girdle + form) Common Name: Tapeworm Habitat: Vertebrate digestive system TAPEWORM Nutrients: Cestodea absorb all of their nutrients from the digestive tract of it’s host. (no mouth)

Tapeworm showing proglottids Mature proglottids

Form and Function: Cestoidea can grow from 1 mm to 30 m in length. (~100 ft) They consist of two main body parts. 1) Scolex (head) -Attachment structure

Tapeworm scolex (head ) light microscope suckers Immature proglottids) hooks

Tapeworm scolex and hooks SEM image I love you

2) Strobila (reproductive body) -Reproduction & Nutrient absorption

Proglottids: each segment of the worm, containing a complete reproductive structure

Dog eats infected flea Worm grows in dog Flea larva eats tapeworm eggs. Tapeworm larvae develop inside flea Proglottids with eggs leave in wastes

Phylum Rotifera (Wheel + to Bear) Common name: Rotifer Habitat: Most freshwater. About 10% marine Solitary, free-swimming Name is derived from the Corona (head)

Rotifer size: 0. 1 -3. 0 mm ~1000 cells large Body type: Triploblastic Bilateral Pseudoceolomate

Eutelic: Organisms that have a fixed number of cells when they reach maturity, the exact number being constant for any one species. Approx 1000 in Rotifers, depending on the species.

Nutrition: Complete digestive tract Excretion with Flame Cells Feed on SOM or small microorganisms Mastax: Jawlike organ that grinds food Ciliated digestive tract helps move food through

Reproduction: Amictic eggs- Summer eggs (thin shelled) Mictic eggs- Winter eggs (thick shelled) Rotifer video 2: 30 Rotifer 1: 30 Rotifer feeding

Phylum Nematoda (thread) Common Name: Roundworm Numbers: ~15, 000 -- 500, 000 species Described Estimated Habitat: Parasitic to plants or animals Some free living

Body type: Triploblastic Bilateral Pseudocoelomate Size: Microscopic -- 2 -5 m long Round in cross section Long slender & tapered at both ends

Nutrition: Feed on ANY type of organic matter. (Carnivorous, herbivorous, omnivorous, saprobes, parasitic) Cuticle provides protection against digestion by host.

Dioecious: Separate sexes. (male & Female) Dimorphic: Each sex has different anatomical characteristics

Class Secernentea 1. Genus Ascarius • Intestinal roundworm, infecting small intestine of humans and other large mammals. • Eggs exit with feces. • Host must eat eggs to become contaminated and continue life cycle. Egg produced by adult exits in host in feces Adult stage in host intestine. Host ingests eggs Migrate to trachea, carried to stomach Hatch in host intestine Molt in lungs Migrate to lungs as larva

2. Genus Entrobius (pinworm) • Most common roundworm in US • Lives in host(human) large intestine • Eggs may be inhaled through infected dust Eggs ingested by host Host gets eggs on fingers Adult migrates to perianal region to lay eggs at night Organism matures in host large intestine Adult lives in host large intestine

Class Adenophorea Genus Necator (hookworm) • Southern US • Feed on blood & tissue fluids • Lays up to 10, 000 eggs daily Eggs hatch in feces Eggs produced Develop into larva in the mud/soil Adult stage in small intestine Swallowed by host Penetrate host skin through toes Matures and migrates to trachea Migrates to lungs Enters circulatory system