Tunicate’s close relationship to vertebrates makes studying them critical for understanding our own evolutionary origins. How this odd-looking creature could be related to vertebrates is hard to imagine were it not for that tadpole beginning. Interestingly, tunicates are the closest relatives of vertebrates, which includes fish, mammals, and even humans.
“This idea that they begin as tadpole-looking larva that, when ready to develop, basically headbutts a rock, sticks to it, and begins to metamorphosis by reabsorbing its own tail to transform into this being with two siphons is just awe-inspiring,” sais Nanglu. In contrast, appendicularians retain the look of a tadpole as they grow to adults and swim freely in the upper waters. They live their adult life attached to the seafloor. Most ascidiaceans begin their lives looking like a tadpole and mobile, then metamorph into a barrel shaped adult with two siphons. There are two main tunicate lineages, ascidiaceans (often called “sea squirts”) and appendicularias. After the animal feeds, the other siphon expels the water. One of the siphons draws in water with food particles through suction, allowing the animal to feed using an internal basket-like filter device. An adult tunicate’s basic shape is typically barrel-like with two siphons projecting from its body. Tunicates are truly strange creatures that come in all shapes and sizes with a wide variety of lifestyles. In a new study in Nature Communications, Nanglu and coauthors describe the new fossil, named Megasiphon thylakos, revealing that ancestral tunicates lived as stationary, filter-feeding adults and likely underwent metamorphosis from a tadpole-like larva. It’s just as cool,” said Nanglu, postdoctoral researcher in the Department of Organismic and Evolutionary Biology at Harvard University. “This animal is as exciting a discovery as some of the stuff I found when hanging off a cliffside of a mountain, or jumping out of a helicopter. But his latest subject may hold first place status for a while: a 500-million-year-old fossil from the wonderfully weird group of marine invertebrates, the tunicates. Karma Nanglu says his favorite animal is whichever one he’s working on.
view moreĬredit: Original artwork by Franz Anthony In the background is the hemichordate Oesia, which lived in perforated tubes. Nearby brachiopods (bottom center) and the spiny sponge Choia (center middle) are common in many Cambrian environments. Also reconstructed in the vicinity are other species commonly found in the Marjum Formation, the site from which M. thylakos was also sessile (non-moving) and spent its time filter feeding using its prominent siphons. Image: Artistic reconstruction of Megasiphon thylakos, a benthic organism that lived directly on the seafloor.
0 kommentar(er)
