BI256 Lecture Notes - Lecture 13: Nerve Plexus, Turbellaria, Symmetry In Biology
Document Summary
Cladogram platyhelminthes lack a single unique character so not monophyletic. Characteristics: phylum platyhelminthes: no clear de ning feature, marine, freshwater and moist terrestrial habitats, turbellarians most free-swimming; rest entirely parasitic, bilateral symmetry; body attened dorsoventrally, triploblastic, acoelomate, epidermis cellular or syncytial (ciliated in some). Produce adhesive secretions that attach anchor cells to substratum. Bear strain of attachment and allow subtle muscular contractions to pull animal forward. Secretes chemicals that release anchor cell attachment. An inverted agellated cell ( ame cell) sitting in a mesh cup (tubule end) Mesh = cellular interdigitation between ame cell and terminal tubule cup. Flagellar beat created negative pressure and draws uid in through mesh. Fluid is ultra ltered then future modi ed in tubule system. Modi ed uid is eliminated though excretory pores - nephridiopores. Less important role as an excretory system (metabolic waste removal) Different degrees of organization from simple nerve plexus (like cnidarians) to nerve cords + a primitive brain;
