The leaves, which are borne in pairs at the tumid nodes, are oval in form and have a Dicotyledonous type of venation.
There are some pleasing passages in Arnobius, but on the whole he is a tumid and a tedious author.
The long, slender stems, somewhat tumid at the nodes, were ribbed, the ribs running continuously through the nodes, a fact correlated with the superposition of the whorled leaves, the number of which in each verticil was some multiple of 3, and usually 6.
In some species certain of the legs bear on their ventral sides furrows with tumid lips and lined by smooth non-tuberculate epithelium; they are called coxal organs, and it appears that they can be everted.
The tentacles surround an area known as the peristome, in the middle of which there is an elongated mouth-opening surrounded by tumid lips.