Isotomodes productus is a common and widespread soil species that reaches a maximum length of 0.9 mm. Isotomodes bisetosus is white in colour, has an oval post-antennal organ (PAO) and is eyeless (Fig. 1). A characteristic (shared with Isotomodes trisetosus) is the presence of two prominent setae (Fig. 2) on the dorsal side of the fifth abdominal segment (which are absent in Isotomodes bisetosus and Isotomodes templetoni). The furca is about the same length as the head and the mucro has two teeth (Fig. 3). The ventral side of each dens has a single seta (cf. six ventral setae on the ventral side of the dens of Isotomodes trisetosus).
Fig. 1 (above): Post-antennal organ (PAO) of Isotomodes productus collected from Fatfield in July 1940 by Bagnall.
Fig. 2 (above): Isotomodes productus collected from Cultra, Co. Down, Ireland in September 1936 by Litster and Bagnall. There are two prominent setae (*) on the dorsal side of the fifth abdominal segment.
Fig. 3 (above) : Furca of Isotomodes productus collected from Cultra, Co. Down, Ireland in September 1936 by Litster and Bagnall. The mucro (mu) has two teeth and the ventral side of each dens (d) has a single seta (ds). ma, manubrium
