A fold of the endoderm, which projects into the blood cavity of ascidians. See Tunicata.
Grooves on the pharyngeal sack of urochordates and hemichordates, containing cilia and thick mucus, which filter food particles from the water siphoned into the pharynx and carry them to the esophagus for digestion. Synapomorphy of the Chordata.
a glandular ciliated groove along the ventral side of the pharynx in Urochordata, Cephalochorda, and lamprey larvae.