Ascidians belong to the Phylum Chordata, and are classified as Protochordates.
Although Ascidians do not have a vertebral column when they are adults, their juvenile larvae show features in common with the vertebrates.
Free-swimming larvae have a notochord (pre-vertebral column), a dorsal nerve chord, and pharyngeal clefts or gill slits.
These features are lost or modified after the juvenile tadpole-like stage settles onto a rock and then grows into the leathery adult stage.
The most common Ascidian on rocky ocean shores is the common Cunjevoi, Pyura stolonifera, otherwise known as the "sea-squirt". It gets its common name from its ability to squirt out a jet of sea water if stepped upon.
The flesh inside the Cunjevoi is used as fish bait by rock fishermen. When you walk across a rocky shore at low tide, you may see many cunjevoi, with many having their tops hacked off.
There are many other ascidians on shores as well, but most are usually hidden under rocks and boulders lying in sand or mud conditions. These species are more common in the marine zone below the levels reached by the lowest tides.
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