Mesopsammon

The body, however, is always extremely slender with a diameter of not more than 500 μ, thus enabling the animals to move through the interstitial system without actively replacing the sand grains; all the listed species, therefore, are considered to be mesopsammon forms sensu Broaden (1962)

The mesopsammon of intertidal environments and the many physical, chemical and mineralogical factors which affect their presence are very complex.

As is the case with mesopsammic representatives of other major taxa, interstitial nemertines constitute a unique biological grouping recognizable by specializations that are characteristic of mesopsammon (see Swedmark, 1964, for review of the nature of interstitial organisms).