Recently, researchers described a 500-million-year-old tunicate fossil species, which suggested that the modern tunicate body plan was already established soon after the Cambrian Explosion.
Why in news?
- The new fossil, named Megasiphon thylakos, revealed that ancestral tunicates lived as stationary, filter-feeding adults and likely underwent metamorphosis from a tadpole-like larva.
- These are commonly called sea squirts which are a group of marine animals.
- They spend most of their lives attached to docks, rocks or the undersides of boats.
- About 3,000 species of tunicate exist in the world’s oceans, living mostly in shallow water.
- They are a species of marine invertebrates with an evolutionary history from atleast 500 million years ago.
- Researchers are interested in them as they are the closest relatives of vertebrates, which includes fish, mammals, and people.
- There are two main tunicate lineages namely;
- Ascidiaceans: They are often called “sea squirts and most ascidiaceans begin their lives looking like a tadpole and mobile, then metamorph into a barrel-shaped adult with two siphons. They live their adult life attached to the seafloor.
- Appendicularias: They retain the look of a tadpole as they grow to adults and swim freely in the upper waters. These seem extremely far removed from vertebrates.
- Tunicates are truly strange creatures that come in all shapes and sizes and have a wide variety of lifestyles.
- An adult tunicate’s basic shape is typically barrel-like, with two siphons projecting from its body.
- One of the siphons draws in water with food particles through suction, allowing the animal to feed using an internal basket-like filter device.
- The other siphon expels the water.
Q1) What are Invertebrates?
Invertebrates are characterized by their lack of a backbone or vertebral column. Instead, they have other structural features that support and protect their bodies. Invertebrates comprise a vast array of animal groups, including insects, spiders, crustaceans, mollusks etc