Darwinhydrus solidus 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 : 394-397

Darwinhydrus solidus Sharp

Instar III

Description. Color: Head capsule predominantly dark brown; narrowly yellow along lateral margin of parietale and frontoclypeus ( Fig. 5 ); head appendages predominantly yellow except apically dark brown mandible; body predominantly dark brown, protergum with a large yellowish macula on each side; siphon yellow to pale brown apically; legs yellow to pale brown, slightly darker over coxae; urogomphus dark brown, pale yellow proximally. Head: Head capsule ( Fig. 5 ) pearshaped, tapering posteriorly, lacking a neck constriction; ecdysial suture well-developed, coronal suture short; frontoclypeus bluntly rounded, spatulate anteriorly, narrow and elongate, with several lateral notches well-visible in dorsal view; 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, subequal in length to 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 shorter 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. 7–8 ), 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. 6 ); 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 longest and narrowest ( Fig. 6 ), projecting backwards into more or less elongate subconical siphon, wellconstricted at point of insertion of urogomphi. Urogomphus very long, composed of 2 urogomphomeres; U1 long, much longer than segment VIII; U2 narrower, setiform, much shorter than U1. 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 60 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 (00) Nasale 0 - broad, subtriangular

1 - narrow, more or less parallel sided

(01) Apex of nasale 0 - not spatulate

1 - spatulate

(02) Frontoclypeus 0 - lateral processes lacking, if present then barely visible in dorsal view

1 - with one lateral process well-visible in dorsal view

2 - with several short lateral processes well-visible in dorsal view

(03) Epicranial plates 0 - separate at the ventral midline

1 - meet on the ventral midline

(04) Seta FR7 0 - spine-like

1 - hair-like

(05) Primary seta FR13 0 - absent

1 - present

(06) Pore FRb 0 - present

1 - absent

(07) Seta PA3 0 - inserted contiguously to setae PA1 and PA2

1 - inserted far from setae PA1 and PA2

(08) Pore PAc 0 - not inserted anteriorly to stemmata

1 - inserted anteriorly to stemmata

(09) Pore PAe 0 - present

1 - absent

(10) Pore PAj 0 - present

1 - absent

(11) Secondary spine-like setae on 0 - present

lateral margin of parietals 1 - absent

(12) Antennomere II 0 - longer than antennomere I

1 - subequal in length to antennomere I

(13) Antennomere III 0 - longer than antennomere I

1 - subequal in length to antennomere I

(14) Antennomere III 0 - spinula absent

1 - spinula present

(15) Seta AN3 0 - inserted distally

1 - inserted submedially

(16) Primary pore ANf 0 - present

1 - absent

(17) Primary pore ANh 0 - present

1 - absent

(18) Cardo 0 - not fused to stipes

1 - fused to stipes

(19) Setae MX 4. MX 5 and MX 6 0 - present

1 - absent

(20) Setae MX 8 and MX 9 0 - present

1 - absent

(21) Pore MXh 0 - inserted on the galea

1 - inserted on the stipes

2 - absent

(22) Prementum 0 - broader than long

1 - as broad as long

2 - longer than broad

(23) Labial palpomere 2 0 - narrow, subcylindrical, narrowing to apex

1 - robust, broadest at midlength

(24) Primary setae LA3, LA4, LA5 0 - articulated distally

1 - articulated proximally

(25) Seta LA6 0 - inserted distally

1 - inserted submedially

(26) Primary seta LA10 0 - articulated medially

1 - articulated distally

(27) Pore LAb 0 - present

1 - absent

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(28) Prementum 0 - lacking secondary setae

1 - with one secondary seta

2 - with several secondary setae

(29) Primary seta TR2 0 - present

1 - absent

(30) Primary pore FEa 0 - present

1 - absent

(31) Dorsal mesofemoral natatory setae 0 - absent

1 - present

(32) Dorsal metafemoral natatory setae 0 - absent

1 - present

(33) Ventral femoral natatory setae 0 - absent

1 - present

(34) Seta TI7 0 - short, spine-like

1 - long, hair-like

(35) Primary pore TIa 0 - present

1 - absent

(36) Natatory posterodorsal setae on tibia 0 - absent

1 - present

(37) Dorsal tarsal natatory setae 0 - absent

1 - present

(38) Ventral surface of abdominal 0 - membranous

segment II 1 - sclerotized

(39) Ventral surface of abdominal 0 - membranous

segment III 1 - sclerotized

(40) Ventral surface of abdominal 0 - membranous

segments IV–V 1 - sclerotized

(41) Ventral surface of abdominal 0 - membranous

segment VI 1 - sclerotized

(42) Siphon 0 - not constricted at point of insertion of urogomphi

1 - strongly constricted at point of insertion of urogomphi (43) Setae AB6 and AB7 0 - short

1 - elongate

(44) Primary pore ABa 0 - present

1 - absent

(45) Siphon 0 - lacking secondary setae ventrally

1 - with secondary setae ventrally

(46) Seta UR5 0 - long, hair-like

1 - short, spine-like

(47) Seta UR8 0 - inserted apically on urogomphomere 2

1 - inserted submedially on urogomphomere 2

2 - inserted proximally on urogomphomere 2

(48) Urogomphomere I 0 - lacking secondary setae

1 - with secondary setae

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. 7–8 ; U with secondary setae ( Fig. 6 ).

Distribution. Endemic to the Republic of South Africa.

Figures

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.