BSC 116 Lecture Notes - Lecture 16: Necator Americanus, Gastrovascular Cavity, Gonochorism
27 Aug 2016
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Molecular phylogenetics has revised our view of animal evolution: lophotrochozoa, ecdysozoa, deuterostomia. There is a wide variety of body plans among animals. Recognized based on several traits: bilateral symmetry: have a head, etc, triploblastic: mesoderm for muscles, etc, most are coelomates: hydrostatic skeletons. Around since before the cambrian explosion: 575 my. Three main groups of phyla: lophotrochozoa, ecdysozoa, deuterostomia. Some taxa have ciliated trochophore type larvae: phylum platyhelminthes: flatworms, phylum annelida: segmented-worms, phylum mollusca: mollusks. Some have a feeding structure called a lophophore: phylum ectoprocta: bryozoans, phylum brachiopoda: lamp shells. Many phyla lacking either: phylum rotifera: rotifers ( wheel animals ) Platyhelminthes is represented by free-living & parasitic flatworms. Flatworms generally long and flat acoelomates: mainly parasitic. Like cnidarians, lack through-gut: gastrovascular cavity: serves for circulation. Unlike cnidarians, have organs to maintain osmotic balance: protonephridia with cells called flame bulbs. Most hermaphrodites: simultaneously male & female: also capable of asexual reproduction.
