Xenylla humicola is common species which is bluish black in colour and reaches 2.0 mm in length. Most records are from seashore debris and accumulated organic matter on the margins of saline water; it can also be extremely abundant on the percolating filters of sewage treatment works inland. Xenylla humicola has a furca in which the mucro/dens boundary is clearly separate (Fig. 1), marked by a notch on the ventral surface. In Figure 43c (p. 87) of Hopkin (2007) this boundary is shown as a line across the dens, which is not quite right (see Fig. 3), and led to Peter Shaw mis-identifying X. humicola until the COI barcode from a "Xenylla maritima" from the Lindisfarne tide line matched a Xenylla humicola from the Arctic. The mucro is long and pointed and is distinctive.
A unique chaetotaxic character is the presence of only 2+2 setae on the ventral side of the head either side of the ventral fluid-conducting channel (3+3 in other Xenylla species) but this is very difficult to see.