Question 1

What is the difference between an acoelomate and a pseudocoelomate body?

Accepted Answer

In an acoelomate body, the region between the alimentary canal and body wall is filled with mesodermal tissue, so no body cavity is present. In a pseudocoelomate body, a fluid-filled cavity is present, but its lining is not completely formed by mesoderm.

Question 2

Why does Planaria not have a proper anus?

Accepted Answer

Planaria has an incomplete and branched alimentary canal with its mouth on the ventral surface near the middle of the body. It opens at the mouth for elimination, but there is no separate proper anus at the opposite end. Its excretory system contains flame cells.

Question 3

How does Taenia differ from Planaria?

Accepted Answer

Both belong to Platyhelminthes and are acoelomate, but Planaria has an incomplete branched gut. Taenia is a cestode and has no alimentary canal at all; it absorbs nutrients through its body surface.

Question 4

What makes the earthworm a true coelomate?

Accepted Answer

The earthworm has a fluid-filled coelom that is lined by mesoderm. Septa divide this coelom internally into successive segmental compartments, corresponding to the external rings of metameric segmentation.

Question 5

What are nephridia in an earthworm?

Accepted Answer

Nephridia are the excretory organs of annelids. In earthworms they remove nitrogenous wastes from the body. The complete body contains 100–120 short segments, so the lab models a clearly identified 12-segment representative portion.

Acoelomate, Pseudocoelomate and Coelomate Body Plans — 3D Animal Kingdom Lab

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