BRANCHIOSTOMA-PHARYNGEAL GILL BARS

The pharyngeal gill bars are of two type primary and secondary- The skeletal rod pf a primary gill bar is called primary gill rod . Its lower end is forked and it encloses a blood vessel and a coelomic canal through out its length. The secondary gill bar develops a small tongue bar which grows downwards from the dorsalwall of a primary gill slits. The skeletal rod  of a secondary gill bar is called secondary gill rod.The primary gill bars are interconnected by a system of transdverse  bars or synapticula which impart a basket like appearance to the pharynx similar to the branchial sac of tunicates. A synapticulum also contains a blood vessel and a skeletal rod.