The remaining animals form a monophyletic group called the Bilateria. For the most part, they are bilaterally symmetric, and often have a specialized head with feeding and sensory organs. The body is triploblastic, i.e. all three germ layers are well-developed, and tissues form distinct organs. The digestive chamber has two openings, a mouth and an anus, and there is also an internal body cavity called a coelom or pseudocoelom. There are exceptions to each of these characteristics, however — for instance adult echinoderms are radially symmetric, and certain parasitic worms have extremely simplified body structures. COUNT 4
QSN1 What is the group of animals that often have a specialized head with feeding and sensory organs called? ANS1 Bilateria QSN2 How many openings in the digestive chamber do animals in the Bilateria group have? ANS2 two QSN3 What are the openings in the digestive chambers for animals in the Bilateria group called? ANS3 mouth and an anus QSN4 What is the internal body cavity of animals in the Bilateria group called? ANS4 coelom or pseudocoelom