ИСТИНА

The unpaired skeleton and the buccal diverticulum are the main supporting structures of collar and proboscis in the Enteropneusta. The skeleton of all enteropneusts includes unpaired anterior plate and paired posterior horns. The buccal diverticulum represents the forward-directed hollow growth of the buccal tube. It consists in most cases of three main parts: the flattened base, the isthmus, and the anterior part. Morphology of the buccal diverticulum is closely connected with that of the skeleton. The features of the diverticulum are the result of the skeleton morphology. The paired skeleton horns separate the flattened diverticulum base from the buccal tube. The buccal diverticulum branches of the gut at the point where the horns fuse. The isthmus of the buccal diverticulum rests on the dorsal side of the unpaired skeleton plate. Paired lateral wings of the isthmus are based on corresponding lateral wings of the skeleton plate. The anterior part of the buccal diverticulum is "stuck" on the rostrum of the skeleton plate and is supported by paired skeleton subiculi. There is a general similarity in the morphology of the skeleton and the buccal diverticulum in different enteropneusts. In spite of this there some differences in details which may play an important role in the taxonomy of the group.