Coelom generally reduced to a system of tubes, sometimes communicating with vascular system; in Acanthobdella and Ozobranchus a series of metamerically arranged chambers as in Oligochaeta.

Ozobranchus possesses a coelom which is less typically chaetopodous than that of Acanthobdella, but more so than in other leeches.

Four (Ozobranchus) to six (Glossiphonia) or ten (Philaemon) are common numbers.

Ozobranchus) than in others, where they are small rounded bodies.

In Ozobranchus the structures in question are still more complicated.

It is at least clear that in Ozobranchus this comparison is justifiable; but only probable, or perhaps possible, in the case of Philaemon.