Identify one of the key external difference between vertebrates and invertebrates. a) vertebrates are always radial symmetrical. b) invertebrates are always bilaterally symmetrical. c) invertebrates are always bilaterally symmetrical, while vertebrates could show either bilateral or radial symmetry. d) vertebrates are always bilaterally symmetrical, while invertebrates could show either bilateral or radial symmetry.

The correct answer is D)

the abdomen (less formally called the belly, stomach, tummy or midriff) constitutes the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. the region occupied by the abdomen is termed the abdominal cavity. the stomach secretes acid and enzymes that digest food. ridges of muscle tissue called rugae line the stomach. the stomach muscles contract periodically, churning food to enhance digestion. the pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.

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