Trochozoa protostome bilaterally-symmetric worms {flatworm} (Platyhelminthes) can have mesoderm, have gastrovascular cavities, have muscular pharynx past mouth, and have reproductive organs.
front and back
Bodies have front and back. They keep back upward.
longitudinal
Bodies are longitudinal, with head, trunk, and tail, requiring body orientation. Head is body part that moves first, holds forward senses, and has mouth.
movement
Flatworms move by cilia, using muscular contraction. Muscles have opposing motions and have rhythms controlled by different cells.
nervous system
Flatworms have one brain ganglion with interconnected ventral nerves. Flatworms fused head ganglia to make brain.
Marine-flatworm brain bimodal neurons can habituate to vibration offset, using vibration-sensitive and tactile-sensitive interneurons. They can habituate to illumination offset, using light-sensitive interneurons.
senses
Flatworms have pigmented eyespot cells and can detect light, smell, and touch.
Flatworms secrete sugary substances {slime}| from gland cells.
Intestinal and blood flatworms have thick outer layers {cuticle, fluke}|.
Planaria excrete through tubes, from intestine to surface pores, which are lined with ciliated cells {flame cell}, to move water and waste out.
Ribbon worms have sections {proglottid} formed by budding behind head.
Male flukes have one slit {schistosome}|, into which smaller female fits.
One-centimeter-long intestinal and blood flatworms {fluke} look like planaria, have suckers, are blood and liver parasites, have no cilia, have thick cuticle, and have generation alternation.
life cycle
Flukes lay eggs, in animal urine or feces, which hatch into larvae {miricadia}. Larvae enter snails and change into different larvae {cercariae}, which can bore into skin, though they have no teeth, and then go to liver. In liver, male and female join {schistosomula} and enter blood to go to intestine and bladder. Adults have covering {tegument} that has few surface proteins but can bind human proteins. Adults can live 30 years.
Common flatworms {planaria}| {planarion} like still fresh water, can be parasites, respire by diffusion, and have tubes with flame cells to move water and waste out. For regeneration, smed-betacatenin-1 gene product indicates head, and Wnt gene product indicates tail.
Ribbon worms {ribbon worm} {tapeworm, animal}| can have suckers, or one ring of hooks, to attach to vertebrate intestines. Tapeworms are ribbon-like, have no mouth, have no digestive system, absorb food, and have proglottids.
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Date Modified: 2022.0225