Coelhydrus brevicollis Sharp, 1882

Alarie, Yves, Michat, Mariano C. & Challet, Gilbert L., 2017, Larval Description and Phylogenetic Placement of the South African Endemic Genera Coelhydrus Sharp and Darwinhydrus Sharp (Coleoptera: Dytiscidae: Hydroporinae: Hyphydrini), The Coleopterists Bulletin 71 (2), pp. 389-401 : 392-394

Coelhydrus brevicollis Sharp

Instar III

Description. Color: Head capsule predominantly yellow to pale brown; nasale creamy white to pale yellow; head appendages predominantly creamy white to pale yellow except mandible dark brown distally; body predominantly brown, except protergum and abdominal terga VII and VIII predominantly yellow; legs predominantly pale yellow; urogomphi yellow to pale brown, lightly darker distally. Body: Subcylindrical, narrowing towards abdominal apex. Measurements and ratios characterizing body shape shown in Table 1. Head: Head capsule ( Fig. 1 ) pear-shaped, tapering posteriorly, lacking a neck constriction; ecdysial suture welldeveloped, coronal suture short; frontoclypeus bluntly rounded, spatulate anteriorly, narrow and elongate, lacking lateral notches; dorsal surface lacking egg bursters (ruptor ovi of Bertrand 1972); epicranial plates meeting ventrally; ocularium present, stemmata not visible ventrally and subdivided into 2 vertical series, stemmata of posterior row more widely spaced; tentorial pits visible medio-ventrally at about midlength. Antenna elongate, slightly shorter than HW; composed of 4 antennomeres, A2 and A3 longest, A4 shortest; A3’ relatively elongate, shorter than A4, A3 with a ventroapical spinula. Mandible prominent, falciform, distal half projecting inwards and upwards, apex sharp; mandibular channel present. Maxilla: stipes short and thick, incompletely sclerotized ventrally; cardo fused to stipes; galea and lacinia absent; MP elongate, subequal in length to antenna, composed of 3 palpomeres; MP1 and MP2 longest, subequal in length, MP3 shortest. Labium: prementum subrectangular, much longer than broad, lacking marginal spinulae; LP elongate, distinctly shorter than MP; composed of 2 palpomeres, LP2 subfusiform, slightly longer than LP1. Thorax: Terga convex, pronotum slightly shorter than meso- and metanota combined, meso- and metanota subequal; protergite subrectangular to subovate, more developed than meso- and metatergites; meso- and metatergites transverse, with anterotransverse carina; sagittal line well-visible on 3 tergites; sterna membranous; spiracles present on mesothorax. Legs: Long ( Figs. 3–4 ), composed of 6 articles (sensu Lawrence 1991); L1 shortest, L3 longest; CO robust, elongate, TR divided into 2 parts by an annulus, FE, TI, and TA slender, subcylindrical, PT with 2 long, slender, slightly curved claws; posterior claw shorter than anterior claw on L1 and L2, posterior claw longer than anterior claw on L3; ventral surface of TI and TA lacking elongate spinulae. Abdomen: 8-segmented ( Fig. 2 ); segments I–II sclerotized dorsally, membranous ventrally; segments III–V sclerotized dorsally, with a ventral plate, segments VI–VIII completely sclerotized, ring-like; all tergites lacking sagittal line, with anterotransverse carina; spiracles present lateroventrally on segments I–VII; segment VIII ( Fig. 2 )

(DARS). l = length; w = width; ** = missing data. longest and narrowest, projecting backwards into short subconical siphon, well constricted at point of insertion of urogomphi. Urogomphus very long, composed of 2 urogomphomeres; U1 long, much longer than segment VIII; U2 narrower, setiform (length of U2 could not be measured as the structure was broken on every specimen studied). Chaetotaxy: Head capsule with numerous secondary setae; lateroventral margin of PA with several secondary spine-like setae; anteroventral margin of nasale with half circle of about 50 lamellae clypeales of different lengths, directed downwards; AN, MX, and LA lacking secondary setae; MN with 1 hair-like secondary seta on basoexternal margin; thoracic and abdominal sclerites I–VIII with numerous secondary setae mainly on posterior half; natatory setae present on dorsal margin of femora, tibiae, and tarsi; secondary leg setation detailed in Table 2 and Figs. 3–4 ; U with secondary setae ( Fig. 2 ).

Distribution. Endemic to the Republic of South Africa.

Description of Larvae of Darwinhydrus Sharp ( Figs. 5–8 )

Diagnostic Combination. The third instar of Darwinhydrus can be distinguished from those of other genera of Hyphydrini that have been associated with adults by the following combination of characters: frontoclypeus with short lateral processes, well-visible in dorsal view; HL = 1.00– 1.50 mm; ratio HL/LAS = 1.90–2.20; ratio MP/LP = 1.60–1.90; ratio A4/A3 <0.30; ratio LP2/LP1 <1.30; metathoracic leg> 3.50 times HW; ratio LAS/HW <0.90; primary setae LA3, LA4, and LA5 articulated distally on prementum; dorsal meso- and metafemoral secondary setae present; procoxa with more than 15 secondary setae; femora, tibiae, and tarsi with more than 8, 10, and 10 dorsal natatory setae, respectively; siphon moderately elongate, clearly constricted at point of insertion of urogomphi, lacking secondary spinelike setae on ventral surface.

Figures

Figs. 1–2. Coelhydrus brevicollis, instar III. 1) Head capsule, dorsal view; 2) Abdominal segment VIII and proximal portion of urogomphi, dorsal view. Scale bars = 0.50 mm.

Figs. 3–4. Coelhydrus brevicollis, instar III, metathoracic leg. 3) Anterior surface; 4) Posterior surface. Scale bar = 0.50 mm.

Figs. 5–6. Darwinhydrus solidus, instar III. 5) Head capsule, dorsal view; 6) Abdominal segment VIII and proximal portion of urogomphi, dorsal view. Scale bars = 0.50 mm.

Figs. 7–8. Darwinhydrus solidus, instar III, metathoracic leg. 7) Anterior surface; 8) Posterior surface. Scale bar = 0.50 mm.