Worms Chapters 26.3, 26.4, and 27.2

Animal Classification Animals Invertebrates Vertebrates Sponges Cnidarians Worms Mollusks Arthropods Enchinoderms Ectotherms (cold-blooded) Endotherms (warm-blooded) Fishes Amphibians Reptiles Birds Mammals Worms - Phylum Platyhelimenthes - Phylum Nematoda - Phylum Annelida

Flatworms Phylum Platyhelimenthes  (Greek) platy = flat  helmins = worm The least complex worm Acoelomates About 14,500 species exist found in marine, freshwater, and land The most commonly studied flatworm is the planarian

Nervous Control Most of the nervous system is located in its head The nervous system consists of two nerve cords that run the length of the body Nerve cords

Nervous Control Eyespots can detect the presence or absence of light Sensory cells can detect chemicals and movement in water Eyespots Sensory cells

Nervous Control Ganglion  A small swelling of the nerve cord  Receives messages from the eyespots and sensory pits, then communicates with the rest of the body Ganglia

Reproduction Most flatworms are hermaphroditic Can reproduce sexually and asexually Sexual reproduction  Two planarians will exchange sperm  Internal fertilization occurs  Zygotes are then released in water where they will hatch

Reproduction Asexual reproduction  Planarians can regenerate when damaged Regeneration – The replacement or regrowth of missing body parts

Feeding and Digestion in Planarians A planarian feeds on dead or slow-moving organisms  Planarians are not parasitic To eat, a planarian extends its pharynx from its mouth  Pharynx – a tube-like, muscular organ (also known as the throat)

Extended pharynx

Feeding and Digestion in Planarians Enzymes breakdown the food outside the body, and then food particles are sucked into the digestive tract Food is digested in individual cells Waste leaves through its one opening (mouth) Planarian’s Pharynx

Feeding and Digestion in Planarians Excretory system – eliminates waste from the body Flame cells – excess water is removed from the body

Feeding and Digestion in Parasitic Flatworms Parasitic flatworms have mouthparts with hooks that keep them attached to their hosts Hook Sucker

Feeding and Digestion in Parasitic Flatworms Parasitic flatworms don’t need a digestive system because they obtain nutrients from food that has been digested by their host Hook Sucker

Tapeworm Scolex – a knob- shaped head Proglottid – detachable, individual sections that contain muscles, nerves, flame cells, and reproductive organs Hook Sucker

Tapeworm Each proglottid can contain up to 100,000 eggs Can reach up to 33 ft in length and contain over 2,000 proglottids Hook Sucker

The larva will enter the snail host for further development Adult flukes First larval stage are found in water Second larval stage Eggs are passed out the intestines Fluke larva can bore through the skin, enter the bloodstream, and move to the intestines Embryo develops in human waste

Roundworms Phylum Nematoda  Greek word nema = thread Found in soil, animal, freshwater, and marine environments More than 12,000 species exist Nearly all plant and animals are affected by parasitic roundworms

Pseudocoelomate Have a complete digestive system with two openings (mouth and anus) Free-living species have well-developed eyespots whereas parasitic species have underdeveloped eyespots

Roundworm Parasites of Humans Ascaris is the most common roundworm infection in humans worldwide More common in subtropical areas Children become infected more often than adults  Timmy plays in a sandbox…

Roundworm Parasites of Humans Pinworms are the most common roundworm parasites in the U.S. Children are the commonly infected Eggs can survive two weeks on the surface

Roundworm Parasites of Humans During night, female pinworms lay eggs around the anus of host Taping the anus before bedtime is one method used to eliminate pinworms

Roundworm Parasites of Humans Trichinella can be ingested in raw or undercooked pork or wild game (turkey) Trichinella can be controlled by properly cooking meat

Roundworm Parasites of Humans Hookworms are common in warm climates where they walk on contaminated soil in bare feet Hookworms cause people to feel weak and tired due to blood loss

Hookworm infection from dogs and cats

Segmented Worms Phylum Annelida  Latin term anellus = “little ring"  Examples: Earthworms, bristleworms, and leeches Coelomates with two body openings

Segmented Worms Can be found in most environments, except in frozen soil and dry, compact sand 15,000 species of segmented worms Earthworm Leech Bristleworm

External Anatomy of an Earthworm Prostomium – a tongue-like lobe above the mouth Clitellum - the swelling of the earthworm near its anterior side Setae - Tiny bristles that help earthworms and britleworms move through soil Mouth Anus

Nervous System Segmented worms have simple nervous systems Some species have eyes and brains All species have nerve cords and ganglia

Internal view of an earthworm

Circulatory Segmented worms have a closed circulatory system – blood flows through vessels to reach all parts of the body  Open circulatory system – blood is not enclosed in vessels throughout the entire body Examples: flatworms and roundworms

Internal view of an earthworm

Respiration Segmented worms must live in water or wet areas because they are able to exchange gases directly through their moist skin

Digestion Annelids have a complete digestive system Have a crop and a gizzard  Crop – a sac that holds soil temporarily before it moves into the gizzard  Gizzard – a muscular organ that grinds food

Internal view of an earthworm

Excretion Annelids have two nephrida in almost every segment that collect waste products and transport them out of the body

Internal view of an earthworm

Reproduction Earthworms and leeches are hermaphrodites During sexual reproduction, worms exchange sperm Eggs are fertilized and laid in the soil The eggs hatch in 2-3 weeks Bristleworms have separate sexes and reproduces sexually

Internal view of an earthworm

Leeches Many species are parasites that suck blood or other body fluids from their hosts Front and rear suckers enable leeches to attach themselves to their hosts

Leeches The saliva contains chemicals that act as a anesthetic  Example – Novocain Other chemicals prevent the blood from clotting Leeches are used medically to remove decaying tissues of patients

Leeches A leech can ingest 2-5 times its own weight in one meal A leech will drop off its host when its full and may not eat again for months