How do the Annelids fit in?. Annelida. Rotifera. Nematoda. Platyhelminthes. Nemertea. Cnidaria. Porifera. unknown common ancestor. Phylum Annelida. the segmented worms. Annelida Characteristics. Triploblastic. Organ level of organization. Bilateral Symmetry. Cephalization.
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the segmented worms
Organ level of organization
No body cavity
Have a “false” body cavity that is surrounded on ONE side only by mesoderm
Blastopore becomes the mouth and the anus forms secondarily
Blastomeres divide at an oblique angle to one another, so that each lies in the furrow created by the cells beneath them
One blastomere is removed
Development is arrested
Split in mesoderm
Many are filter-feeders with specialized structures
Many are predatory with specialized structures
Many construct their own homes out of CaCO3 or sand debris and mucous
Circular muscle contraction
Longitudinal muscle contraction
A saw or leaf spring of a pick-up
Lack septa between metameres, so they are incapable of moving like Oligochaetes.
Instead, they use their anterior and posterior suckers to move.