Limbodessus exilis Watts & Humphreys 2006

(Figs 73–76)

Source of material. Two specimens of instar III were used for the description (Table 1). The larvae were collected at the following locality: Australia, Moore palaeovalley, Maranalgo calcrete, BES 10424/27, 25–V–2004, coll. W. F. Humphreys and C. H. S. Watts. The larvae studied were identified by comparing the sequence of a fragment of the CO1 gene with that from a known adult.

Diagnosis (instar III). Medium-sized species (HL 0.55–1.15 mm); head (Fig. 73) subpentagonal; nasale subtriangular; half-circle of dense spinulae on lateroventral margins of nasale absent; hole-like structure on ventrodistal surface of nasale absent; lateral margins of nasale not inflated in dorsal view; lateral branches of nasale lateral margins of parietal scarce; seta AN2 present; distal half of MN broad; setae LA3, LA4, LA5 and LA8 hairlike; secondary setae on U absent (Fig. 76).

Instar I. Not available.

Instar II. Not available.

Instar III (Figs 73–76). Head (Fig. 73). A3 less than 2.25 times longer than A1; A3 less than 1.45 times longer than A2; MN less than 4.85 times longer than broad; MP less than 1.75 times longer than labial palpus; MP2 2.10– 3.10 times longer than MP3; LP2 more than 0.65 times as long as LP1. Legs (Figs 74–75). L3 2.25–2.85 times longer than HW. Abdomen (Fig. 76). Chaetotaxy. Anteroventral margin of nasale with 49 lamellae clypeales distributed in 2 rows; pro- and mesoCO without anterior secondary setae; pro-, meso- and metaCO without posterior secondary setae; proCO with less than 11 secondary setae; metaCO with less than 20 secondary setae; anterodorsal secondary setae on pro- and metaFE present; metaFE with less than 12 anteroventral secondary setae; posterodorsal secondary setae on meso- and metaFE absent; metaFE with 9–27 secondary setae; anterodorsal and anteroventral secondary setae on proTI present; mesoTI with less than 4 anteroventral secondary setae; metaTI with less than 9 anteroventral secondary setae; posterodorsal secondary setae on proTI absent; metaTI with less than 16 secondary setae; secondary setae on proTA absent; anterodorsal secondary setae on meso- and metaTA absent; anteroventral and posterodorsal secondary setae on meso- and metaTA present; posteroventral secondary setae on mesoTA absent; metaTA with 1–5 posteroventral secondary setae; mesoTA with less than 7 secondary setae; metaTA with less than 16 secondary setae; secondary setae on U absent. Measurements and ratios that characterize the body shape are shown in Table 9. Secondary leg setation detailed in Table 17.

Remarks. Both specimens of L. exilis examined had the second urogomphomere broken, which prevented the evaluation of urogomphal morphometry. Within the stygobitic species studied, L. exilis belongs to the group characterized by the absence of secondary setae on the urogomphus (L. challaensis, L. fridaywellensis, L. hillviewensis, L. hinkleri, L. leysi, L. masonensis, L. millbilliensis, L. morgani, L. ordinarius, L. pulpa, L. raeae, L. windarraensis, L. yuinmeryensis) (Fig. 76). Larvae of L. exilis can be distinguished from any other species of that group by the following combination of characters: lateral margins of the nasale not inflated in dorsal view (Fig. 73), mandibles less than 4.80 times longer than broad, longer legs, absence of posteroventral secondary setae on the pro- and mesotarsus (Fig. 75), and presence of posteroventral secondary setae on the metatarsus.