Enlarge / That blue tube is definitely a really shut relative of vertebrates. (credit score: Gerard Soury)
Beneath the waves, there are unusual, virtually alien creatures that increase questions concerning the evolution of life on Earth and our personal earliest origins. The solutions is perhaps hiding in tunicates.
Tunicates are filter-feeding invertebrates that embrace sea squirts and salps. The extra widespread ascidiacean species are sessile and fasten to rocks or the seafloor, whereas the appendicularian species swim freely. But all of them spawn as larvae that vaguely resemble tadpoles. Motile tunicates are likely to develop into one thing that appears like a bigger model of the larva. The others ultimately faceplant onto a floor and take up their very own tails whereas morphing right into a sessile, tubelike type with two siphons.
Regardless of all this weirdness, there may be now sturdy proof that tunicates are the closest family to vertebrates, however a thriller nonetheless surrounds them. How did they evolve, and what did they evolve from? A 500 million-year-old fossil is now telling us extra concerning the evolution of those peculiar life varieties.
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