No­to­chord

BBC Wildlife Magazine - - Q&A - SB

On the face of it, hu­mans and sea squirts – tubu­lar, rock­cling­ing fil­ter feed­ers – have lit­tle in com­mon. But there’s one fun­da­men­tal fea­ture that groups us to­gether on the tree of life within the phy­lum Chor­data (‘chor­dates’). A no­to­chord is a semi-rigid rod that runs the length of the body, pro­vid­ing an at­tach­ment site for mus­cles. In sea squirts, it is found in the free-swim­ming, tad­pole-like lar­val stage. In ver­te­brates, it has been largely re­placed by the spinal col­umn, although it can still be seen dur­ing our em­bry­onic devel­op­ment.

Sea squirts ab­sorb their spine-like no­to­chords.

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