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Chapter 33

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Christoph Richter

Chapter 33 NotesAs a group protostomes live in about every habitat that you might explore They also include two of the most important model organisms in all of biological science the fruit fly Drosophila melanogaster and the roundworm Caenorhabditis elegans When gastrulation occurs in protostomes the initial pore that forms in the embryo becomes the mouth If a coelom a body cavity forms later in development it forms from openings that arise within blocka of mesodermal tissue Phylogenetic studies have long supported the hypothesis that protostomes are a monophyletic group meaning the protostome deveopmental sequence arose just onceTwo major subgroups exist within the protostomes The two monophyletic groups of protostomes are called the Lophotrochozoa and the Ecdysozoa WHAT IS A LOPHOTROCHOZOANThe 13 phyla of lophotrochozoans include the mollusks annelids and flatworms The groups name was inspired by morphological traits that are found in some but not all of the phyla in the lineage1A feeding structure called a lophophore which is found in three phyla and2A type of larva called a trochophore which is common to many of the phyla in the lineageMolluscs are largest groupGastropodaCephalopodaBivalviaPolyplacophoraA lophophore is a specialized structure that rings the mouth and functions in suspension feeding They are found in bryozoans moss animals brachipods lamp shells and phoronids horshoe worms Trochophores are a type of larvae common to marine mollusks annelids that live in the ocean and several other phyla in the Lophotrochozoa A trochophore larva has a ring of cilia around its middle These cilia allow swimming and in some species sweep food partiles into the mouth Trochopore originated early in the evolution of Lophotrochozoans though different larval types evolved later in some groups
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