Unlock the fascinating world of flatworms with our comprehensive document! Dive into the intricate details of these simple yet extraordinary creatures, exploring their biology, habitats, and unique behaviors. Perfect for students, educators, and nature enthusiasts, this document offers in-depth ins...
Free-living freshwater and marine species
Body structure:
Body of it is flattened dorso-ventrally
o Gives the name of the phylum
Simplest animals to show bilateral symmetry
as they move actively, the head goes first
most of sensory cells are collected in the anterior part
o enables the animal to assess area before entering
nerve cells form groups in the front part of the body
o they are called ganglia
forerunners of the brain
cephalization: process of formation of the head with a brain during evolution
bilaterally symmetrical animals with regulatory center (ganglia or brain) are more
efficient in
o feeding
o locomotion
o mating
other advances over other simpler invertebrates (sponges, cnidaria)
o three embryonic germ layers
third layer is mesoderm located between ectoderm and endoderm
layers develop and give rise to various specialized tissues of the adult
animal
o two types of tissue combine to form organs
lack respiratory and circulatory organs
o gas exchange takes place by diffusion
diffusion: passive movement of particles from high to low concentration
digestive cavity has evolved into branched gut
o single opening into a mouth
this single oral opening takes in food (ingestion) and releases excrement (egestion)
o process of digestion is not very efficient due to lack of anus
protostomes: invertebrates that have an oral opening that develops from the opening
of the primordial digestive cavity. Protostomes are all worms, mollusks, arthropods
deuterostomes: some invertabrates and all vertebrates where the oral opening doesn’t
develop from primordial digestive cavity and changes into an anus, but appears
somewhere else on the embryo
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