565mya Tunicates

 Sea tulips are tunicates with colourful bodies supported on slender stalks. Sea squirts are so named because of their habit of contracting their bodies sharply and squirting out water when disturbed. Sea liver and sea pork get their names from the resemblance of their dead colonies to pieces of meat.

A Sea squirt resemble a sedentary bag of sea water anchored to a rock. It feeds on food particles strained from water. Anatomically, the sea squirt looks very different, that is, until its larvae are examined. The sea squirt larva looks and swims like a tadpole. it possesses a notochord and a dorsal nerve tube, and moves by undulating its post-anal tail from side to side. Vertebrates may have branched off from ancient sea squirt larvae via neoteny.  The tadpole-like larvae are free-swimming. The muscular tail contains a notochord (a flexible, rodlike structure common to all vertebrates) and a nerve cord. When the larva finds a place to metamorphose, it attaches itself by a sucker located at the anterior end of the body. Later the tail, with its notochord and nerve cord, is absorbed and disappears. Although as adults most sea squirts are sessile, some can move by attaching with one area of the body and letting go with another.  This represents a link between animals without a spinal cord to those with one eventually being protected by a vertebral column, a common feature to all vertebrates.