But at present the word "leech" is applied to every member of the group Hirudinea, for the general structure and classification of which see Chaetopoda.
They possess (save for certain Archiannelida, most Hirudinea, and other very rare exceptions) setae or chaetae implanted in epidermal pits.
Thus the body cavity is divided into a sequence of chambers by transverse septa; and even among the Hirudinea, Spadella cephaloptera (Busch).
There are, however, further complications in some forms. Especially are these to be seen in the more modified Oligochaeta and in the much more modified Hirudinea.
They contrast with those of the Oligochaeta and Hirudinea by reason of their frequently close association with the gonads, the same organ sometimes serving the two functions of excretion and conveyance of the ova and spermatozoa out of the body.
