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The prehistoric chordate, the Ascidian or sea squirt.

Sea Squirt

The prehistoric chordate, the Ascidian or sea squirt.

"Gastrulation of an Ascidian. I. Vesicular Morula of an Ascidian flattened and about to undergo gastrulation. II. Gastrulation effected. fh, cavity of the morula, or blasto-invagination; ch, dd, large blastomeres of the hypoblast, inclosed in small blastomeres of the epiblast." -Whitney, 1911

Sea Squirt Gastrulation

"Gastrulation of an Ascidian. I. Vesicular Morula of an Ascidian flattened and about to undergo gastrulation.…

Diagram of a longitudinal section through a tunicate or ascidian (sea squirt).

Tunicate

Diagram of a longitudinal section through a tunicate or ascidian (sea squirt).