this is a terrible course do not take it

platyhelminthes: flatworms

• simplest animals with bilateral symmetry

• shows cephalization

• no circulatory or respiratory system

  • uses diffusion to transport oxygen and nutrients

• single opening (pharynx) to digestive system (gastrovascular cavity)

• still primitive but has more developed organ systems than porifera + cnidarians

• 3 cell layers

  • ectoderm: outside

  • mesoderm: middle

  • endoderm: inner

• 2 types of flatworms: parasitic & free-living

planaria: free-living

• mostly marine; some fresh water with few on land

• has nerve network with concentration at anterior end

  • ganglia (clusters of nerves) detect and respond to light and chemicals (eg. food)

• pharynx extends from mouth with enzymes to break down food

  • pharynx: strong tube sucking food into cavity, leftovers ejected from the mouth

• digestion occurs in gastrovascular cavity

  • forms intestines with many branches

    • for diffusion, digested food diffuses into nearby cells from cavity

• flame cells: specialized tube network for excreting water through pores

• cilia allows for movement in water

• eyespot: senses light changes

parasites: internal & external

• have specialized hooks/suckers to latch onto host

• fragmentation, can self-fertilize

  • proglottid (small sections of worms, up to 100k eggs) leave through host feces

• often sacrifice some organ systems to enhance others

  • digestive & nervous systems often lost/reduced

    • no mouth or circulatory system

    • enhances reproductive system

• tapeworms: in host's intestines

  • absorbs nutrients through body wall

  • most of worm is for egg production

    • larva form cysts in muscle tissue of intermediate hosts

• flukes: liver flukes

  • commonly affects sheep, cattle, and humans in the tropics

  • eg. swimmer’s itch

  • carried by a vector, often snails

nemotoda: round worms

• important link in food chain

  • aerates soil, has parasitic relationship with animals, plants, and humans

• simplest animal to have a complete digestive tract with 2 openings (mouth & anus)

• has pseudocoelom (central body cavity with organs) but lacks peritoneum (no mesoderm cell lining)

• free-living (soil, aquatic, polar, tropics, hot springs)

• some are parasitic

• has simple nervous system (ganglia) in head region

  • transmitting sensory information

  • controlling movement

  • detecting chemicals

annelida: segmented worms

• separated by septa (sing. septum) [internal walls]

• segments mostly identical, some modified for specialized functions

  • eg. 1st segment may have eyes, antennae, etc.

• have true coelom (central body cavity lined with peritoneum)

• closed circulatory system with heart, blood vessels, and hemoglobin (carries o2)

  • heart-like ring muscles work to pump blood

  • 2 major vessels

    • ventral blood vessel: blood going towards posterior end, from head to tail

    • dorsal blood vessel: blood going towards anterior end, from tail to head

• has nervous system + is cephalzied

  • has small brain located under pharynx

  • central nerve cord from brain runs through entire body

    • similarly to all organ systems, penetrating septum and running through worm’s entire body

    • ganglion: swelling of ventral nerve cord in each segment

  • specialized areas in digestive system (esophagus, pharynx, gizzard, intestines)

    • gizzard: holds food

    • intestines: breaks down nutrients

  • metabolic wasted excreted by nephridia in each segment

    • nephridia: similar to small kidneys

  • has no respiratory organs

    • breathes through moist skin, which has cuticles to retain moisture

      • cuticule: thin waterproof layer

  • locomotion

    • muscular system has both circular and longitudinal muscles

      • circular muscles contracting results in worm becoming skinnier

      • longitudinal muscles contracting results in worm becoming shorter