What best describes the tissue organization of chordates?

What best describes the tissue organization of chordates?

• A. Diploblastic
• B. Triploblastic, Eumetazoa
• C. Pseudocoelomate
• D. Acoelomate

Answer: (B)

Chordates are organized with three germ layers that give rise to true tissues and organs. This triploblastic development means there are ectoderm, mesoderm, and endoderm layers early in embryogenesis, each forming different tissues: the ectoderm becomes skin and nervous system, the endoderm lines the gut, and the mesoderm gives rise to muscles, skeleton, and other organs. Because chordates have these three layers and true tissues, they are classified as eumetazoa. The other descriptions focus on different aspects. Diploblastic organisms have only two germ layers and lack many of the tissues and organs seen in chordates. Acoelomate and pseudocoelomate refer to the presence and type of body cavity rather than the tissue-layer structure, whereas chordates possess a true coelom derived from mesoderm. So the best fit for tissue organization is the combination of three germ layers with true tissues, i.e., triploblastic, eumetazoa.

Chordates are organized with three germ layers that give rise to true tissues and organs. This triploblastic development means there are ectoderm, mesoderm, and endoderm layers early in embryogenesis, each forming different tissues: the ectoderm becomes skin and nervous system, the endoderm lines the gut, and the mesoderm gives rise to muscles, skeleton, and other organs. Because chordates have these three layers and true tissues, they are classified as eumetazoa.

The other descriptions focus on different aspects. Diploblastic organisms have only two germ layers and lack many of the tissues and organs seen in chordates. Acoelomate and pseudocoelomate refer to the presence and type of body cavity rather than the tissue-layer structure, whereas chordates possess a true coelom derived from mesoderm. So the best fit for tissue organization is the combination of three germ layers with true tissues, i.e., triploblastic, eumetazoa.