Biology 11 – Kingdom Animalia Study of the Primitive Worms Phylum Platyhelminthes: Flatworms Phylum Nematoda: Roundworms BIOL 316 Phylum Platyhelminthes

Phylum Platyhelminthes – the Flatworms The Planarians The Flukes The Tapeworms

Importance of the Flatworms to Evolution Bilateral body plan – left side mirror image of right Cephalization – development of the head sense organs and nerves concentrated in head region Centralization of nervous system: Nerve cord accompanies cephalization and bilateral symmetry. Advanced muscle tissue present; Primitive excretory system allows removal of metabolic wastes

Flatworms (Phylum Platyhelminthes) Definition: Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have 3 embryonic germ layers, bilateral symmetry, and cephalization Flatworms are acoelomates, meaning “without a coelom”  coelom = a fluid-filled body cavity that is lined with mesoderm  mesoderm = middle germ layer that gives rise to muscles, circulatory, reproductive, and excretory systems

Phylum Platyhelminthes Characteristics Bilateral symmetry; anterior and posterior ends. Body flattened Well-developed epidermis No internal body cavity other than digestive tube (acoelomate) Parenchyma (connective tissue) fills space between organs. Incomplete digestive system Still one opening This critter eats and poops out of its mouth – mmmm, pass the popcorn

Cross Section of a Flatworm

Advantage of Being Flat Surface area to volume ratio is important for organisms. Many substances enter and leave through body surface. Faster absorption and release of wastes 3mm Volume = 3 x 3 x 3 = 27mm2 Area = 6(3 x 3) = 54mm3 9mm 3mm 1mm Volume = 9 x 3 x 1 = 27mm2 Area = 2(9 x 1) + 2(3 x 1) + 2(3x9) = 78mm3

Nutrition and Digestion Typical digestive system includes a mouth, a pharynx, and an intestine. Parasitic Tapeworms and Flukes lack a digestive system Parasitic flatworms, such as the Tapeworm absorb molecules from host. Free living flatworms (Planarians) are carnivorous; suck prey into pharynx with mouth. Undigested food goes out mouth. Yes, folks, they eat and excrete out the same hole 

Flatworm Respiratory, Circulatory, and Excretory System Lack circulatory, respiratory, and excretory systems. Flatworms rely on diffusion to transport oxygen and nutrients throughout the body, to remove CO2 and other wastes Some flatworms have flame cells – specialized cells that remove excess water and metabolic wastes

Nervous System and Sense Organs Have a nerve-net. Most have more complex system. Cerebral ganglion = primitive brain coordinates impulses. “Ladder” system carries impulses throughout body Many sense organs present Eyespots Chemoreceptors, touch sensors and rheoreceptors (sense direction) also common

Note: Free-living vs. Parasitic Free-living (eg Planarians) have well developed digestive and nervous systems to seek-out and process food Parasitic Tapeworms – rely on host’s digestive system to process food, which absorb. No need for advancement of nervous system – not needed.

Reproduction – in Free-living Flatworms such as Planarians May reproduce sexually or asexually Asexual: Binary fission – split in two Sexual: Both sexes present in same flatworm (hermaphrodites). Fertilization internal, eggs produced Embryos emerge as juveniles resembling adults.

Reproduction in theTapeworm! Lack digestive system Sucker and hooks on anterior end for attachment Neck produces new segments Called proglottids Each proglottid contains male and female gonads Reproductive output high Many proglottids per worm Many eggs per proglottid

Groups of Flatworms Turbellarians Free-living, e.g. planarian Flukes (Trematoda) Parasites Tapeworms (Cestoda)

Tapeworm - Life Cycle

Flukes -- Life Cycle of a Liver Fluke

The Coelom or Body Cavity Advances

Another Look at the Coelom

Phylum Nematoda (Roundworms) Definition: Roundworms are unsegmented worms that have pseudocoeloms and digestive systems with two openings – a mouth and an anus Pseudocoelom = “false coelom” Is a body cavity between the endoderm and mesoderm tissues, partially lined with mesoderm tissue

Form and Function in Roundworms Feeding: free-living carnivores; or eat algae, fungi, decaying organic matter Respiration: gases diffuse through body walls Circulation: no internal transport system  diffusion Excretion: metabolic wastes diffuse through body walls

Form and Function in Roundworms Response: ganglia from the head and run through length of body; sense organs to detect chemicals of other organisms Movement: muscles and fluid of the pseudocoelom function as a hydrostatic skeleton; allows movement (swimming or pushing through soil) Reproduction: sexual reproduction; internal fertilization, were male deposits sperm inside the female’s reproductive tract

Roundworm Ecological Roles Omnivores that catch and eat algae, fungi, decaying matter Recyclers Parasites of Plants – eg. The Golden Nematode attacks potato crops, causing severe devastation Parasites of animals

Ascaris – Parasitic Roundworm of Pigs and Humans

Unfortunately, they can Grow quite Big!

Parasites: Your Pet's Enemies Tiny parasites that pose a gigantic threat   Heart worms inside the dog's heart, can grow to a length of 14". What they do: Restrict blood flow and cause organ damage. Symptoms include coughing. labored breathing, heart failure. Untreated, heart worm disease can kill a dog. Death may occur within 72 hours. How they spread: Transmitted by over 70 species of mosquitoes. Virtually all dogs are at risk. Defending against them: Once a month prevention is recommended, contact your local veterinarian for advice.

Adult roundworms live in the dog's small intestine Adult roundworms live in the dog's small intestine. What they do: Cause diarrhea, vomiting, stunted growth, rough coat, bloated belly. How they spread: Almost all puppies get roundworms from their mothers. Dogs can also pick up roundworms from the soil. Defending against them: Once a month prevention is recommended, contact your local veterinarian for advice.

Enlarged hook worm mouth showing 'teeth' Enlarged hook worm mouth showing 'teeth'. What they do: Attach to the dog's intestinal lining, leaving bleeding internal wounds. Cause blood loss, anemia, and diarrhea. As few as 100 hook worms can kill a puppy. How they spread: Eggs pass through the feces of an infected dog into the soil where they are easily swallowed or can penetrate through a dog's feet. Defending against them: Once a month prevention is recommended, contact your local veterinarian for advice.

Symptoms: Larvae digested enter bloodstream and burrow into organs, causing absolutely horrendous pain and in some cases death.

Filarial (threadlike worms) are nematodes that may block the passage of Fluids in the Body Disease: Elephantitis The disease is caused by parasitic worms, including Wuchereria bancrofti, Brugia malayi, and B. timori, all transmitted by mosquitoes. Lymphatic filariasis currently affects 120 million people worldwide, and 40 million Blocks Lymphatic nodes which drain fluid to and from the blood. Tropics, Africa and Asia

Phylum Annelida (Earthworms) Annelida  annellus, meaning “little ring” Definition: Annelids are worms with segmented bodies. They have a true coelom that is lined with tissue derived from mesoderm.

Body Plan The body of an annelid is divided into segments separated by septa (singular: septum) Septum – internal walls between each segment Most segments contain the same organs (eyes, antennae, sense), while others are specialized Most segments have bristles called setae

Feeding and Digestion Annelids may be filter feeders or predators (carnivorous) Annelids use their pharynx (with jaws) to bring food into the esophagus. The food then go into the crop (food storage) and then to the gizzard (food is ground up). Then food is absorbed in the intestine.

Circulation Annelids have a closed circulatory system. Blood is contained in a network of blood vessels Blood circulates through a dorsal vessel and a ventral vessel, and smaller blood vessels through each segment Dorsal vessel helps pump blood

Respiration Annelids can respire through: Gills (worms that live in water) Diffusion through skin (earthworms)

Excretion Digestive waste passes out anus Metabolic waste is filtered out by nephridia

Response Most annelids have a well-developed nervous system with a brain and nerve cords Other sense organs: Sense receptors, chemical receptors, sensors that detect gravity

Movement Hydrostatic skeleton Contraction of longitudinal and circular muscles Annelids can burrow, use setae, or parapodia (paddlelike appendages for swimming or crawling)

Reproduction Sexual reproduction May have separate sexes and external fertilization OR Annelids are hermaphrodites and exchange sperm with another worm Two worms attach, exchange sperm, and store it in sacs A clitellum (a thick band) secretes a mucus ring where the egg and sperm are released and fertilization takes place inside this ring The ring falls off the worm and forms a cocoon, where the eggs will hatch

Ewwwwwwwwwwwwwwwwwwwwwwwww! Ah, but they are sooooooo in love, don’t you think?

Class Oligochaeta Earthworms Streamlined bodies, few setae, live in soil or water

Class Hirudinea Leeches External parasites that suck blood and body fluids of host Medical uses: reduce swelling, helps blood clotting Have suckers at one or both ends for attachment. Produce a chemical in saliva called HIRUDIN, which is an anti-coagulant

Leech Anatomy 101 Mmmm – lunch! 

Leeches Used in Medicine Successful reattachment of severed ear, as blood continued to flow and carry nutrients to the damaged region

Class Polychaeta Sandworms, blood worms Marine annelids with parapodia (paired paddlelike appendages)

Ecology of Annelids Annelids are important for our environment because they: Burrow through the soil, aerating and mixing it Decompose plant matter Food source (for birds, moles, toads, snakes, etc.)