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Terms in this set (23)
began about 700 million years ago, in the sea, and today exhibits a diversity of forms.
meaning there is no plane of body symmetry;
meaning the body parts radiate from the center
meaning the organism has a left and right side, in addition to an anterior and posterior end.
is a body cavity, a fluid-filled space located between the digestive tract and the outer body wall.
A true body cavity is completely lined by mesoderm tissue, the "middle" layer of embryonic tissue.
Animals may be acoelomate (lacking a body cavity),
(having a body cavity only partially lined by mesoderm),
(having a true body cavity lined by mesoderm).
represent the descendants of the most ancient animals.
is a relatively simple animal, with radial symmetry
(a digestive compartment with a single opening serving as both mouth and anus)
The "head end" of the worm is called the
The "back" or "top" side of the animal is called the
"belly" is called the ventral
The very first segment of the worm is called the
dorsal blood vessel
is located on the dorsal surface of the gut.
7 to 14, there are 5 pairs of hearts that wrap around the esophagus.
Near the hearts
there are 3 pairs of large, light-colored structures.
Each segment of the worm contains a pair of little tubes called
has six legs. It also has a protective, nonliving covering called the exoskeleton
there are small pores in the exoskeleton called spiracles, which allow the grasshopper to breathe.
tend to be larger than males, and have a forked structure at the end of their abdomen called the ovipositor. They use the ovipositor to dig into soil and deposit their eggs.
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