Question

In the Arrow Worms (the Chaetognaths) what forms first anus or mouth?

Answer 1

In Arrow Worms (Chaetognaths), the mouth forms first, followed by the anus.

Step-by-step explanation:

In Chaetognaths, the mouth develops before the anus during embryonic development. These marine predators have a distinct body plan, with a prominent head and grasping spines. During their early developmental stages, the blastopore, the opening of the gastrula stage in embryonic development, gives rise to the mouth. This forms at the anterior end, while the anus develops later, posteriorly. This process is known as protostome development, where the blastopore becomes the mouth. The formation of the mouth first is a characteristic feature in many protostomes, which includes a wide range of invertebrates. This sequence of development impacts their digestive system and overall physiology. While variations exist among different species, the precedence of mouth formation over the anus remains consistent in Chaetognaths.

Correct answer: In Arrow Worms (Chaetognaths), the mouth forms before the anus.

Answer 2

Arrow Worms' development, whether the mouth or anus forms first, depends on their protostome or deuterostome classification, but their unique characteristics make it unclear without specific studies.

Step-by-step explanation:

In the development of Arrow Worms (the Chaetognaths), we can determine whether the mouth or anus forms first by looking at their classification as either protostomes or deuterostomes. The defining feature of protostomes is that the mouth develops at the blastopore (the first opening in the developing embryo), whereas in deuterostomes, the anus forms at the blastopore, and the mouth forms secondarily. However, when it comes to Chaetognaths, they exemplify unique developmental characteristics that do not fit neatly into these categories, which has led some scientists to place them in a separate category altogether. The final clarification would require specific developmental studies on Arrow Worms to confirm their classification.