Which of the following animal groups does not have tissues derived from mesoderm? a. annelids b. echinoderms c. cnidarians d. flatworms

Verified step by step guidance

1. Identify the key term: Mesoderm is one of the three primary germ layers in the early embryo. The mesoderm gives rise to tissues such as muscle, bone, and blood.
2. Understand the development of tissues in different animal groups: Animals with tissues derived from mesoderm are typically triploblastic, meaning they develop three primary germ layers during embryonic development (ectoderm, mesoderm, and endoderm).
3. Recognize the characteristics of the animal groups listed: Annelids, echinoderms, and flatworms are triploblastic and thus have tissues derived from mesoderm.
4. Identify the exception: Cnidarians, such as jellyfish and corals, are diploblastic, meaning they only develop two primary germ layers (ectoderm and endoderm) and do not have a mesoderm layer.
5. Conclude which group does not have tissues derived from mesoderm: Based on the characteristics of diploblastic organisms, cnidarians do not have tissues derived from mesoderm.

Key Concepts

Germ Layers

Germ layers are the primary layers of cells in an embryo that develop into different tissues and organs. In triploblastic organisms, there are three germ layers: ectoderm, mesoderm, and endoderm. The mesoderm is particularly important as it gives rise to muscles, circulatory systems, and other internal structures. Understanding the role of these layers is crucial for identifying which animal groups possess or lack specific tissue types.

Mesoderm

The mesoderm is the middle germ layer in triploblastic organisms, situated between the ectoderm and endoderm. It is responsible for forming various structures, including muscles, bones, and the circulatory system. Animals that lack mesoderm, such as cnidarians, are classified as diploblastic, having only ectoderm and endoderm. Recognizing the presence or absence of mesoderm helps in categorizing animal groups based on their developmental biology.

Diploblastic vs. Triploblastic

Diploblastic organisms have two germ layers (ectoderm and endoderm), while triploblastic organisms possess three layers, including mesoderm. This distinction is fundamental in animal classification, influencing their body plans and complexity. Cnidarians, such as jellyfish and corals, are examples of diploblastic animals, whereas annelids, echinoderms, and flatworms are triploblastic. Understanding these classifications aids in answering questions about tissue development in various animal groups.