Limbodessus millbilliensis Watts & Humphreys, 2006

Michat, Mariano C., Alarie, Yves & Watts, Chris H. S., 2012, 3584, Zootaxa 3584 (1), pp. 1-110 : 59-60

Limbodessus millbilliensis Watts & Humphreys, 2006

( Figs 115 –133)

Source of material. One specimen of instar I, one of instar II and two of instar III were used for the description ( Table 1). The larvae were collected in association with adults at the following localities: Australia, Carey palaeovalley, Lake Violet calcrete, Wiluna Gold, Bore Field, observation bore for pump 1, BES 7148, 26.675S, 120.23194E, 18–V–1999, coll. W. F. Humphreys and H. J. Hahn ; Lake Violet calcrete, Wiluna Gold, Bore Field, BES 6437, 26.675S, 120.23194E, 9–V–2001 ; Millbillie Station , MB for pump 3, BES 14317, 26.6801S, 120.2248E, 18–IX–2006, coll. W. F. Humphreys and T. Moulds.

Diagnosis (instar III). Medium-sized species (HL 0.55–1.15 mm); head (Fig. 129) subpentagonal; nasale subtriangular; half-circle of dense spinulae on lateroventral margins of nasale absent; hole-like structure on ventrodistal surface of nasale present (Fig. 130); lateral margins of nasale inflated in dorsal view; lateral branches of nasale minute; slender spinulae anterior to seta FR13 absent; occipital foramen well developed (HW/OCW less than 1.90); occipital suture present; lateral margins of parietal straight; secondary spiniform setae on lateral margins of parietal scarce; seta AN2 present; distal half of MN narrow; setae LA3, LA4, LA5 and LA8 hair-like; secondary setae on U absent (Fig. 133).

Instar I ( Figs 115–128 ). Head ( Figs 115–123 ). Cephalic capsule not strongly elongate (HL/HW less than 1.55); seta PA3 inserted far from setae PA1 and PA2; A3 more than 2.80 times longer than A1; A3 more than 2.25 times longer than A2; MP2 1.55–1.85 times longer than MP1; MP2 1.95–2.65 times longer than MP3; LP2 1.40– 2.00 times longer than LP1. Legs ( Figs 124–125 ). L3 less than 2.85 times longer than HW. Abdomen ( Figs 126– 128 ). U less than 3.45 times longer than LAS; U less than 2.35 times longer than HW; U1 1.10–1.40 times longer than U2. Chaetotaxy. Frontoclypeus with 14 lamellae clypeales; additional setae on U absent. Measurements and ratios that characterize the body shape are shown in Table 2.

Instar II. Head. A3 less than 2.50 times longer than A1; A4 less than 0.70 times as long as A3; MN more than 4.90 times longer than broad; MP2 1.05–1.45 times longer than MP1; MP2 2.10–2.95 times longer than MP3; LP2 1.00– 1.70 times longer than LP1. Legs. L3 2.25–2.95 times longer than HW; CL(L3) less than 0.40 times as long as TA. Abdomen. U less than 2.80 times longer than LAS; U less than 2.15 times longer than HW; U1 less than 1.45 times longer than U2. Chaetotaxy. Anteroventral margin of nasale with 31 lamellae clypeales distributed in a single row; anterior secondary setae on proCO absent; meso- and metaCO with less than 5 posterodorsal secondary setae; ventral secondary setae on proCO present; ventral secondary setae on mesoCO absent; proFE with less than 3 posteroventral secondary setae; metaFE with less than 11 secondary setae; secondary setae on proTI absent; anterodorsal secondary setae on meso- and metaTI present; meso- and metaTI with less than 2 posterodorsal secondary setae; posteroventral secondary setae on meso- and metaTI absent; metaTI with less than 5 secondary setae; secondary setae on proTA absent; posterodorsal secondary setae on meso- and metaTA present; posteroventral secondary setae on meso- and metaTA absent; metaTA with less than 4 secondary setae; secondary setae on U absent. Measurements and ratios that characterize the body shape are shown in Table 6. Secondary leg setation detailed in Table 14.

Instar III (Figs 129–133). Head (Fig. 129). A3 more than 2.50 times longer than A1; A3 less than 1.45 times longer than A2; MN more 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 131–132). L3 2.25–2.85 times longer than HW. Abdomen (Fig. 133). U 2.40–3.10 times longer than LAS; U 1.55–2.25 times longer than HW; U1 0.70–1.40 times as long as U2. Chaetotaxy. Anteroventral margin of nasale with 56 lamellae clypeales distributed 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 secondary setae on proTI present; anteroventral and posterodorsal secondary setae on proTI absent; mesoTI with less than 4 anteroventral secondary setae; metaTI with less than 9 anteroventral secondary setae; metaTI with less than 16 secondary setae; secondary setae on proTA absent; anterodorsal and posteroventral secondary setae on meso- and metaTA absent; anteroventral and posterodorsal secondary setae on meso- and metaTA present; 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 10. Secondary leg setation detailed in Table 18.

Remarks. Limbodessus millbilliensis is a very distinctive stygobitic species. It belongs to the group characterized by the absence of secondary setae on the urogomphus ( L. challaensis , L. exilis , L. fridaywellensis , L. hillviewensis , L. hinkleri , L. leysi , L. masonensis , L. morgani , L. ordinarius , L. pulpa , L. raeae , L. windarraensis , L. yuinmeryensis ) (Fig. 133). The species is unique in that the distal half of the mandible is narrower than in the other species studied ( Figs 121 , 129). Also, other characteristic features are the lateral margins of the nasale inflated in dorsal view (shared with L. hinkleri and L. leysi ) (Fig. 129), the presence of a hole-like structure on the ventrodistal surface of the nasale (well visible both in instars II and III) (Fig. 130), and the absence of slender spinulae on the ventral surface of the nasale, anterior to seta FR13 (shared only with L. hinkleri ).

Figures

FIGURES 115–123. Limbodessus millbilliensis, first-instar larva. 115, cephalic capsule, dorsal aspect; 116, cephalic capsule,

FIGURES 124–128. Limbodessus millbilliensis, first-instar larva. 124, left metathoracic leg, anterior aspect; 125, right metathoracic leg, posterior aspect; 126, abdominal segment VIII, dorsal aspect; 127, abdominal segment VIII, ventral aspect; 128, right urogomphus, dorsal aspect. Scale bars = 0.07 mm.