![]() ![]() So, in a recent study by Martin-Duran and colleagues (2012) in which they followed the development of this engimatic worm, they found … drum roll … that priapulids develop as Deuterostomes, with the blastopore forming the anus. You see, the big evolutionary question is which came first, Protostome development or Deuterostome development? Which is the original condition in the common ancestor? Knowing this would inform our understanding of how other changes in development downstream from this evolutionary event were effected, and what we should predict to see in various animal lineages. What does all this have to do with Priapulids? Everything. The development of the mouth and anus in Protostomes and Deuterostomes. Something that may make you groan all the more is the fact that we vertebrates are members of the Deuterostomes. As I like to tell my students, Deuterstomes develop from the bottom up – you may now groan. In the other group, called Deuterostomes (meaning “mouth second”), the blastopore becomes the anus and the digestive tract stretches from hind to fore, eventually “punching” through the head region to form the mouth. ![]() The word Protostome means “mouth first.” Protostomes include a huge variety of animals such as insects, crustaceans, earthworms, mollusks, and most other “creepy-crawlies” you are familiar with. In one group called Protostomes, the blastopore becomes the mouth, and the gut tract develops until it “punctures” the other end of the animal, forming the anus. Yes, even we humans develop a blastopore as the beginning of our gut tract.Īmong the bilaterian animals, there has traditionally been a split proposed that divides these organisms into two groups based on a fundamental difference in the way their digestive tracts develop. That somewhere is a puckered indentation called a blastopore that forms early during their embryonic development. This involves the formation of a gut tube, and like all tubes it has to start somewhere. You may not appreciate it, but one of the key developments of bilaterian animals is forming a distinct mouth and anus. ![]()
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