Chapter 24, Problem 16A

Summary Introduction

Introduction:

Animal body plans with bilateral symmetry include the gut, which is either a sac within the body or a tube flowing through the body, where food is digested. A saclike gut has one opening i.e. a mouth for food intake and waste disposal. A tube-like gut has a mouth and anus opening at both sides, and is a complete digestive organ.

Answer to Problem 16A

Correct answer :

The correct answer is option (B) deuterosome

Explanation of Solution

Explanation/justification for the correct answer :

Option (B) deuterosome. The final outcome for each cell inside the embryo can be altered during the development of deuterosomes. Each cell in the early embryo will form a new embryo if removed. During the embryonic growth in the eight cells stage, the top four cells are placed directly on the bottom four cells. So, the correct answer is option (B).

Explanation for incorrect answer :

Option (A) acoelomate. Acoelomates are other species without a coelom. The acoelomate body plan is derived from the ectoderm, mesoderm, and endoderm. So, this is an incorrect option.

Option (C) protostomes. The final outcome for each cell inside the embryo cannot be altered during the development of protosomes. If one cell is removed from the embryo, the embryo does not grow into a normal larva. The top four cells are offset from the bottom four cells in the eight-cell stage of embryonic development, thereby giving the embryo a spiraling form. So, this is an incorrect answer.

Option (D) pseudocoelomate. Pseudocoelom is a cavity of the body filled with fluid that forms between the mesoderm and the endoderm instead of forming entirely inside the mesoderm as in coelomates.So, this is an incorrect answer.

Conclusion

When one cell is removed during its early development, deuterostome develops into a complete animal. Hence, the correct answer is Option (B) deuterostome