USABO Biosystematics Questions and Verified Answers | Passed | A+

Calcarea, Silicea (sponges) : Lack true tissues; have choanocytes (collar cells-flagellated cells that ingest bacteria and tiny food particles) Cnidaria (hydras, jellies, sea anemones, corals) : Unique stinging structures (nematocysts) housed in special cells (cnidocytes); diploblastic, radially symmetrical, gastrovascular cavity Plathyhelminthes : Dorsoventrally flattened, unsegmented acoelomates; gastrovascular cavity or no digestive tract Rotifera (rotifers) : Pseudocoelomates with alimentary canal (digestive tube with mouth and anus); jaws (trophi) in pharynx; head with ciliated crown 2 Lophophorates: Ectoprocta, Brachipoda : Coelomates with lophophores (feeding structures bearing ciliated tentacles) Mollusca (clams, snails, squids) : Coielomates with three main body parts (muscular foot, visceral mass, mantle); coelom reduced; most have hard shell made of calcium carbonate Annelida (segmented worms) : Coelomates with segmented body wall and internal organs (except digestive tract, which is unsegmented) Nematoda (roundworms