Metamerism Definition

Metamerism is the repetition of homologous body segments. This type of development can be seen in the Annelids, which are earthworms, leeches, tubeworm, and their relatives. It is also seen in a more advanced form in the Arthropods, or crustaceans, insects and their relatives. Metamerism arises from teloblastic development, in which cells divide asymmetrically to form rings of small cells around the embryo. These cells proliferate into the many segments of worms, and can be homonomous meaning very similar, or they can be differentiate into a wide variety of functions. These segments are called heteronomous. Metamerism has led to a great diversity of annelids, arthropods and other segmented animals in the world. The simple segmented condition of annelids allows them to exist in every environment from the deepest parts of the ocean to the soil of some of the highest mountains.

  • Segmentation – A form of development in which many identical portion proliferate rapidly then grow.
  • Homonomous – Simple, and very similar segments produced in worms and related animals.
  • Heteronomous – Highly differentiated segments, as seen in many insects and crustaceans.


1. Scorpions, king crabs, earthworms, and fleas are all segmented animals. They have varied levels of differentiation between the segments. Which of the following terms describes all of the animals?
A. Metamerism
B. Homonomous Segmentation
C. Heteronomous Segmentation

Answer to Question #1
A is correct. All of these animals show metamerism, or a segmented body plan that arises from teloblastic development. The scorpion, crabs, and fleas all belong to Arthropoda, and show heteronomous segmentation. The earthworm shows mostly homonomous segmentation, though certain areas are specialized for reproduction and other tasks.