The hypobranchial tract extends mid ventrally the entire floor of pharynx. It forms a shallow groove with four longitudinal tracts of mucus-secreating gland cells with five tracts of ciliated cells. The cilia of the median tract are the longest. The endostyle is supported below by two gelatinous skeletal plates under which is present the sub-endostylar coelomic canal contaning the ventral aorta.
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