Isotomodes bisetosus is known only from a single locality among beach line grass on Iona. The single specimen in the NHML slide material was collected by Harold Gough in June 1970 and is 0.8 mm in length. Isotomodes bisetosus is white in colour, has an oval PAO and is eyeless. A characteristic (shared with Isotomodes templetoni) is the absence of the two prominent setae on the dorsal side of the fifth abdominal segment (which are present in Isotomodes productus and Isotomodes trisetosus). The furca is about the same length as the head and the mucro has two teeth (Fig. 1). The ventral side of the dens has two setae (cf. four ventral setae on the ventral side of the dens of Isotomodes templetoni).

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Fig. 1 (above): Isotomodes bisetosus collected from Iona in June 1970 by Harold Gough. The mucro (mu) has two teeth and each dens (d) bears two ventral setae (*). ma, manubrium.