Glareadessus stocki Wewalka and Biström

Alarie, Yves & Wewalka, Günther, 2001, Description Of The Mature Larva Of Glareadessus stocki Wewalka And Bistrom (Coleoptera: Dytiscidae), A Stygobiontic Bidessini From The Persian Gulf Region, The Coleopterists Bulletin 55 (2), pp. 144-151 : 145-149

Description of Instar III of Glareadessus stocki Wewalka and Biström

Figs. 1–5

Diagnostic Combination: body fusiformate; stemmata present but slightly reduced in size; cephalic capsule not constricted at level of occipital suture ( Fig. 1 ); antennomere 2 lacking secondary setae; antennomere 3 with a ventroapical spinula, lacking pore ANf; maxillary cardo absent, primary seta MX 1 inserted on maxillary stipes; primary seta MX 5 lacking; prementum lacking lateral spinulae; primary seta TR2 of trochanters absent ( Fig. 4 ); spinulae present on ventral margin of protarsus, otherwise lacking; legs lacking natatory setae ( Figs. 4–5 ); posterotransverse carina lacking on thoracic terga of instar III; siphon strongly constricted posterior to insertion of urogomphi, and short, about 0.30 times LLAS ( Fig. 2 ); primary seta UR2, UR3, and UR4 almost equally distant urogomphomere 1 ( Fig. 3 ); urogomphomere 1 lacking secondary setae ( Fig. 3 ).

Description, Instar III ( Figs. 1–5 ). Colour. Body lightly pigmented, creamy white to pale yellow.

Head. ( Fig. 1 ). HL = 0.63 mm (n = 3); HW = 0.44–0.46 mm (mean = 0.45 mm, n = 3); FCL = 0.49–0.50 mm (mean = 0.49 mm, n = 3); cephalic capsule ( Fig. 1 ) longer than broad (HL/HW = 1.39–1.44), pear­shaped, tapering posteriorly, not contricted at level of occipital suture; HW/OcW = 1.40– 1.44; ecdysial suture well­developed, coronal suture short, 0.21–0.23 times HL; occipital suture present; frontoclypeus bluntly rounded, broad (FCL/FCW = 2.83–3.17), 0.77–0.79 times as long as HL, with lateral notches visible in dorsal view; ventroapical margin of frontoclypeus with ≈ 20 spatulate setae (lamellae clypeales of Bertrand 1972); lateroventral margin with several lateral spine­like bulges (=denticles of Perkins (1980)) visible in dorsal view; ocularium present, stemmata slightly reduced in size, subdivided into 2 vertical series, not visible ventrally, stemmata of the posterior row more widely spaced; tentorial pits visible ventrally on each side of middle at about midlength; antenna 4­segmented, shorter than HW (length of antenna/HW = 0.77–0.78); A2 ≈ A3> A1 ≈ A4, A2/A3 = 0.91–0.94; lateral elongation of antennomere 3 subequal in length to antennomere 4 (A3'/A4 = 0.87–0.91); antennomere 3 with a ventroapical spinula; mandible falciform, not toothed on inner margin, curved inward and upward apically, 0.47–0.49 times HL, 4.24–4.80 times longer than broad; maxilla, maxillary stipes short and thick, incompletely sclerotized ventrally; cardo, galea and lacinia absent; maxillary palpus 3­segmented, slightly shorter than antenna (length of antenna/ length of maxillary palpus = 1.14–1.17); MX 1> MX 2> MX 3, palpomere 2, 0.82–0.83 times as long as palpomere 1; labium, prementum subtrapezoidal, slightly indented medially along anterior margin, ≈ 1.80 times broader than long, lacking lateral marginal spinulae; labial palpus 2­segmented, shorter than maxillary palpus (length of maxillary palpus/length of labial palpus = 1.30–1.33), palpomere 2 subfusiform, 1.07–1.10 times length of palpomere 1; chaetotaxy and porotaxy, primary pore ANf and MX 5 lacking; seta MX 1 articulated on maxillary stipes; head appendages lacking secondary setae except for 1 lateroproximal seta on mandible.

Thorax. Pronotum trapezoidal dorsally, ovate laterally, widest at posterior margin; length of pronotum about 2 times length of mesonotum; metanotum subequal to mesonotum in length, both slightly wider than pronotum; pronotum without transverse carina; both meso­ and metathoracic terga with an anterotransverse carina; tergal setation well­developed on lateral and posterior margin; ventral surface of thoracic segments membranous; presence of spiracular openings not determined.

Legs ( Figs. 4–5 ). 5­segmented; meso and metathoracic legs longest, ≈ 1.10 times length of prothoracic legs, 2.24–2.34 times HW; femur> coxa> tibia ≈ tarsus> trochanter; tarsus with two claws, posterior claw slightly shorter than anterior claw on pro­ and mesothoracic legs, slightly longer on metathoracic leg; posterior metathoracic claw ≈ 0.40–0.43 times as long as metatarsus; chaetotaxy and porotaxy, primary seta TR2 lacking; spinulae present on ventral margin of protarsus; natatory setae absent; position and number of secondary setae as expressed in Table 1 .

Abdomen ( Fig. 2 ). 8­segmented; maximum width of body at level of metathorax and abdomen segments 1 to 3; LLAS = 0.19–0.24 mm (mean = 0.22 mm, n = 3); segments 1–6 dorsally sclerotized, segment 7–8 completely sclerotized; all terga with an anterodorsal transverse carina and with long setae along lateral and posterior margins; presence of spiracular openings not determined; segment 8 short, LLAS/HW = 0.44–0.53, with siphon strongly constricted posterior to insertion of urogomphi; siphon short, bluntly rounded apically, 0.26–0.33 times LLAS; chaetotaxy and porotaxy, secondary tergal setation reduced.

Urogomphus ( Fig. 3 ). Two­segmented; total length of urogomphus (=Uro1 + Uro2') = 0.98–1.00 mm (mean = 0.99 mm, n = 2) (length of urogomphomere 1 = 0.63–0.67 mm (mean = 0.65 mm, n = 2 )); 2.19–2.20 times HW (length of Uro1/HW = 1.41–1.47) and 4.18–4.36 times LLAS (length of Uro1/ LLAS = 2.68–2.93); urogomphomere 1 longer than urogomphomere 2 (Uro1/ Uro2' = 1.79–2.04); chaetotaxy and porotaxy, all primary setae and pores of generalized larva present; primary setae UR2, UR3 and UR4 almost equally distant; secondary setae absent.

Biological Notes. This species occurs in groundwater of wadis. It was collected in gravel banks using B.­R. pumps, 75–100 cm under the surface ( Wewalka and Biström 1998).

Distribution. Oman.

Figures

Figs. 1–3. Glareadessus stocki Wewalka and Biström, Instar III. 1) head capsule, dorsal aspect; 2) last abdominal segment, dorsal aspect; 3) urogomphus, dorsal aspect. Scale bar = 0.10 mm.

Figs. 4–5. Glareadessus stocki Wewalka and Biström, metathoracic legs, Instar III. 4) anterior face; 5) posterior face. Sensillar series: AV = anteroventral, AD = anterodorsal, PD = posterodorsal, Pr = proximal; PV = posteroventral. Scale bar = 0.10 mm.