Platyhelminthes • General characteristics: • Known as “flat worms.” • Body plan: acoelomate, bilateral symmetry • Habitat: aquatic or in host’s body
Platyhelminthes • Nutrition: • Parasitic - (blood, tissue, or predigested materials from host’s intestines) OR • Scavengers and Saprobes
Platyhelminthes • Feeding: • Planarians extend pharynx from mouth • Parasites have specialized mouth parts to attach to their host.
Platyhelminthes • Digestion: • Extracellular: food is pumped into digestive cavity or gut and cells digest and absorb nutrients, digested food is then diffused into the other body tissue • Excretion: diffusion through the body wall • planarians have flame cells to excrete water and wastes through pores
Platyhelminthes • Respiration and Circulation: Diffusion of gases through the skin, skin must remain moist
Platyhelminthes • Nervous: most have ganglia (mass of nervous tissue), eyespots, sensory lobes and respond to touch and chemicals • Demostratescephalization, nervous tissue is concentrated in the head region.
Platyhelminthes • Reproduction: • Sexual Reproduction: • Hermaphrodites • Parasitic worms require hosts to reproduce • Sexual reproduction exchange sperm, internal fertilization
Primary host (human) Intermediate host(snail) Schistosome Life Cycle Section 27-1 Flukes mature and reproduce sexually in the blood vessels of human intestines. Embryos are released and passed out with feces. Adult fluke Human intestine Embryo Ciliated larva Tailed larva After asexualreproduction, newlarvae are releasedfrom the snail into the water. They then infect humans, the primary host, by boring through their skin. Once in the water, embryos develop into swimming larvae that infect an intermediate host (snail). Shistosomiasis
Platyhelminthes • Reproduction: • Asexual reproduction through fragmentation or fission.
Platyhelminthes • Mobility: • Cilia for gliding • Muscle cells controlled by nervous system to react to stimuli
The Anatomy of a Flatworm Eyespot Freshwater flatworms have simple ganglia and nerve cords that run the length of the body. The excretory system consists of a network of tubules connected to flame cells that remove excess water and cell wastes. Ganglia Head Nervecords Gastrovascularcavity Flatworms use a pharynx to suck food into the gastrovascular cavity. Digested food diffuses from the cavity into other cells of the body. Eyespots in somespecies detect light. Excretorysystem Ovary Testes Mouth Pharynx Most flatworms are hermaphrodites, having male reproductive organs (testes) and female reproductive organs (ovaries) in the same organism. Flame cell Excretorytubule
Platyhelminthes • Common Examples: • Turbellaria (Planarian) • Trematoda (Fluke) • Cestoda (Tapeworm)
Nematoda • General characteristics: • Known as “round worms”. • Pseudocoleomate • long and slender, tapered at both ends • protostomes • bilateral symmetry • Body is covered in a complex cuticle
Nematoda • Habitat/Nutrition: • Parasites • Feeding • Both mouth and anus connected by digestive tube • Digestion: takes place in digestive cavity, digested food diffuses into other body tissue. • May also have digestive sacs that food is pumped into for digestion.
Nematoda • Circulation and Respiration: Diffusion of gases through the skin • Excretion: Canal system, diffusion through body wall or out through mouth • Nervous: simple nervous system, with a main ventral (belly) nerve cord and smaller dorsal (back) nerve cord
Nematoda • Reproduction: • Sexual • usually dioescious (separate sexes) • internal fertilization • genders differ in size, shape and color • Parasitic worms require host
Nematoda • Mobility: Muscles along body wall for movement
Nematoda • Examples: • Hookworms • Pinworms • Guinea worms
Annelida • General characteristics: • Known as “segmented worms” • Coelomates • Habitat: aquatic and moist soil
Annelida • Nutrition: heterotrophic, filter feeders, parasites, scavengers, and saprobes • Feeding: Pharynx used to obtain food • Carnivorous species have two or more sharp jaws
Annelida • Digestion: extracellular, takes place in intestine • Earthworm: pharynx → esophagus→ crop (storage) → gizzard (ground) → intestines (absorption)
Annelida • Excretion: • Digestive wastes pass out through the anus • Cellular wastes containing nitrogen is passed out by the nephridia (simple kidney)
Annelida • Circulation: • closed (blood contained in vessels)
Annelida • Respiration: • Aquatic: breathe through gills • Land dwellers: diffusion through skin (must stay moist) typically secrete a mucus to keep skin moist
Annelida • Nervous: • Best developed sense organs in free living marine organism • Well developed nervous systems consisting of brain and spinal cord • Two or more pairs of eyes, sensory tentacles, chemical receptors and statocysts that help detect gravity
Annelida • Reproduction • Most sexually • Some use external fertilization and have separate sexes • Earth worms and leeches are hermaphroditic, but rarely fertilize their own eggs
Annelida • Mobility • Two major groups of muscles that function as part of the hydrostatic skeleton • Longitudinal and circular muscles, move by alternating contractions • Earthworms have hair-like structures called setae that allow them to easily grip a surface. • Marine worms have parapodia to use for swimming and crawling
Anus Setae Body segments Dorsalblood vessel Gizzard Crop Clitellum Mouth Brain Ganglion Circular muscle Ventralblood vessel Ringvessels Reproductiveorgans Ganglia Nephridia Longitudinalmuscle Section 27-3
Annelida • Examples: • Earthworms • Leeches • Marine worms