Dicyrtomina saundersi is one of the commonest and most widely collected / photographed Collembola in the UK. Many of the most anthropomorphic images of Collembola are of this species, which appears to be smiling when seen face-on in a photomicrograph.)
Apart from the shape of the patch of pigment at the posterior end of the abdomen (Figs. 1, 2), Dicyrtomina saundersi (Figs. 3, 4) is identical in appearance and morphological characters to Dicyrtomina ornata. In Dicyrtomina ornata, there is a solid patch of dark pigment at the posterior end of the abdomen whereas in Dicyrtomina saundersi, this patch has a distinctive pattern (Figs. 1, 2). Neither Steve Hopkin nor Lubbock before him were convinced that Dicyrtomina ornata and Dicyrtomina saundersi are separate species, but recent molecular evidence (Fanciulli et al 2001) suggests that they are. Consequently, several of the literature records on the map for Dicyrtomina ornata represent Dicyrtomina saundersi. and vice versa.
The visual distinctiveness of our 2 species of Dicyrtomina is sufficiently clear, and the records sufficiently frequent, that the apparent increase of D. saundersi at the expense of D. ornata over the last 150 years may reflect a genuine shift in their population balance in the UK.
Members of the Dicyrtomidae are characterised by having a very short fourth antennal segment (Fig. 1). In species of Dicyrtomina, the claw on the foot is wrapped in an outer membrane and the empodium is wide and bears a short filament that reaches just beyond the tip of the claw (Fig. 2). The inner and outer edges of the mucro are serrated (Fig. 3). The thick spines on the body are relatively short (Fig. 4).
Confusing the picture is a trans-atlantic difference in definitions. In the USA, all these 3 Dicyrtoma 'species' are referred to as subspecies of Dicyrtomina minuta, hence Dicyrtomina minuta saundersi. Happily, molecular work on this group is continuing, so we should get a better idea of the validity of these colour-pattern Dicyrtominas as time progresses.
Species of Dicyrtomina seem to have sexual dimorphism in the colour patterns, though this remains to be confirmed. Males tend to be much darker. Frans Janssens on this page suggests that the typical male colour pattern is dark cheeks, though pale-cheeked males are known and can also be distinguished visually.