Platynectes (Gueorguievtes) davidorum, Hájek & Alarie & Šťastný & Vondráček, 2019

Hájek, Jiří, Alarie, Yves, Šťastný, Jaroslav & Vondráček, Dominik, 2019, The first hygropetric Platynectes and its larva from eastern China (Coleoptera: Dytiscidae), Acta Entomologica Musei Nationalis Pragae (Acta. Ent. Mus. Natl. Pragae) 59 (1), pp. 217-228 : 221-226

Platynectes (Gueorguievtes) davidorum sp. nov.

( Figs 2–23 , 26 )

Type locality. China, Fujian Province, Nanping Prefecture, Wuyishan Mountains, Tongmu – Sangang village, ca. 27°45.0′N, 117°40.7′E.

Type material. HOLOTYPE: ♁ ( IZCAS), labelled: ‘ CHINA: FUJIAN prov., 23.v.-3.vi.2018 / Wuyishan Mts. NNR, Sangang vill. env. / 27°45.0′N, 117°40.7′E, 720 m / river valley; wet rock along road / J.Hájek, D.Král, J.Růžička & L.Sekerka lgt.// NMPC-COL-442 [DNA voucher number;p] // HOLOTYPE ♁ / PLATYNECTES / davidorum sp.nov. / J. Hájek et al. det. 2019 [p, red label]’. PARATYPES: 4 ♁♁ 5 ♀♀, same label data as holotype ( JSCL, NMPC); 1 ♀, same label data as holotype but with additional label ‘NMPC-COL-441 [DNA voucher number; p] / BOLD DNMPC572-19 [BOLD Process ID]’ ( NMPC); 1♀, same label data as holotype, but ‘Yandong Chen lgt.[p]’ ( IZCAS); 1♀, labelled:‘ CHINA: FUJIAN prov., 23.v.-3. vi.2018 / Wuyishan Mts. NNR, Sangang vill. / 27°45.0′N, 117°40.7′E, 720 m / river valley, mixed forest+bamboo; at light / J.Hájek, D.Král, J.Růžička & L.Sekerka lgt. ( NMPC); 1 ♀ ‘Mt. Yandangshan / Wenzhou City / Zhejiang Prov. / alt. 150-350m / 30-V-2006 / LI & SHEN leg. [p]’ ( SNUC).All paratypes with the respective red printed label.

Material of larvae. 1 larva of instar I, 2 larvae of instar II and 5 larvae of instar III, same locality data as holotype ( NMPC, YALC). Two larvae of instar III with additional label ‘NMPC-COL-439 [DNA voucher number; p]’, NMPC-COL-440 [DNA voucher number; p]’.

Description of adult. Male holotype. Habitus ( Fig. 2 ) elongate oblong oval, distinctly convex with continuous outline, broadest before elytral midlength, dorsally convex. Dorsal surface submatt due to distinct reticulation.

Colouration. Dorsal surface black with orange-reddish marking: head with pale clypeus, large triangular spot on frons between eyes and two oval spots on vertex; pronotum with pale anterior corners and indistinctly translucent anterior margin; elytra with indistinct pale lateral band beginning after elytral midlength, shortly interrupted subapically, and with small preapical spot. Ventral surface black with reddish-brown basal half of epipleura and indistinct spots laterally on abdominal ventrites. Appendages reddish-brown.

Head. Moderately broad, ca. 0.65× width of pronotum, transversely elliptical.Anterior margin of clypeus truncate. Antennae with antennomeres rather broad, only slightly longer than wide; club-shaped. Eyes emarginate anterolaterally. Punctation double; several large setigerous punctures present in fronto-clypeal grooves and in depressions along inner margin of eyes; fine punctures distributed sparsely and irregularly on head surface, mostly in intersections of reticulation. Reticulation deeply incised consisting of heterogeneous, longitudinally somewhat elongated, polygonal meshes; meshes mostly closed, usually with several micropunctures inside. Microreticulation present only on vertex posterior to eyes.

Pronotum. Transverse, broadest at posterior angles. Anterior angles acute, posterior angles obtusely rectangular. Sides slightly and evenly curved, with distinct lateral beading. Anterior margin straight (dorso-frontal view), posterior margin slightly sinuate. Punctation double, similar to that of head; row of coarse setigerous punctures present along anterior and basal margin (except for medially); fine punctures distributed irregularly on pronotal surface, presenting mostly in intersections of reticulation. Reticulation similar to that of head, consisting of heterogeneous polygonal meshes; meshes sometimes not closed (especially on disc), usually with several micropunctures inside; meshes larger and less impressed on disc, becoming much smaller and deeply impressed near sides. Microreticulation barely perceptible, occurring only near sides. Centre of pronotal disc with small indistinct longitudinal furrow.

Scutellar shield broadly triangular.

Elytra broadest at midlength, sides evenly rounded, lateral margin distinctly bordered. Punctation double; coarse punctures present in two relatively distinct longitudinal discal lines and irregular lateral line, few punctures present also along suture; fine punctures distributed irregularly over elytral surface, occurring mostly in intersections of reticulation. Reticulation well impressed, similar to that of head and pronotum, consisting of heterogeneous polygonal meshes; meshes sometimes not closed, usually with several micropunctures inside. Microreticulation weakly impressed, more apparent laterally and apically, consisting of heterogeneous polygonal meshes.

Legs. Meso- and metafemora with bunch of spiniform setae along posterolateral margin. Pro- and mesotibia widened, club shaped, densely punctured with spinigerous punctures over ventral surface. Metatibia with two lines of coarse spinigerous punctures over ventral surface. Proand mesotarsomeres 1–3 moderately dilated, ventrally with adhesive setae. Metatarsal claws subequal; anterior (lateral) claw slightly shorter than posterior (medial) one. Surface of legs with distinct reticulation consisting of elongate oblique or transverse meshes. Elongate natatorial setae present along dorsal margin of all tibiae and pro- and mesotarsomeres (although in a lesser number), and along both dorsal and ventral margins (especially dorsal margin) of metatarsomeres.

Ventral surface. Genae reticulated with transverse meshes. Prosternum sinuate anteriorly, obtusely keeled medially. Lateral portions of prosternum with transverse reticulation. Prosternal column shiny, with sparse double punctation; slopes of prosternal column densely and coarsely punctate. Prosternal process shortly lanceolate, in cross-section slightly convex; distinctly bordered in basal half, apex pointed; surface with irregular sparse double punctation. Medial part of metaventrite without microsculpture, shiny, with sparse fine punctation; lateral parts of metaventrite (‘metasternal wings’) slender, tongue-shaped, transversely reticulated. Ratio WC/WS = 4.1. Metacoxal lines well impressed, incomplete anteriorly, almost parallelsided. Metacoxal plates reticulated with polygonal meshes, punctation consisting of sparse fine punctures.Abdominal ventrites I–V with reticulation consisting of longitudinal (I), oblique (II) or transverse (III–V) meshes; ventrites III–V additionally with numerous fine transverse wrinkles medially. Punctation double; bunch of coarse setigerous punctures present in centre of ventrites III–V, additional setigerous punctures arranged sparsely in transverse line in medial part of ventrites; fine punctures distributed sparsely and irregularly on ventrite surface, predominantly on border lines of meshes of reticulation. Apical abdominal ventrite (VI) with posterior margin regularly rounded, distinctly beaded; reticulation present only baso-laterally; surface of disc with fine transverse wrinkles; with short and deep longitudinal grooves along posterior margin; punctation double, coarsely punctured along posterior margin, sparsely and finely punctured on disc.

Male genitalia. Median lobe ( Fig. 4 ) in lateral aspect simple, sickle-shaped, distinctly setated subapically along both ventral and dorsal margins; apex slightly broadened, asymmetrical. Parameres ( Fig. 5 ) slender, densely setated dorsally, with a distinct subbasal tooth on ventral side; left paramere more slender than the right one.

Female differs from male in the following characters: meshes of dorsal surface reticulation more deeply engraved and longitudinally stretched, surface appearing more matt, interstices more densely punctate; abdominal ventrite VI with sublateral rugose area large, punctures confluent, forming several longitudinal grooves, medially not rugose and densely punctate; pro- and mesotibia less widened; pro- and mesotarsomeres 1–3 not dilated and without adhesive setae.

Measurements (N = 14). TL: 4.9–5.4 mm (mean value: 5.1 ± 0.2 mm); holotype: 5.0 mm. Tl-h: 4.4–4.9 mm (mean value: 4.6 ± 0.2 mm); holotype: 4.5 mm. MW: 3.0– 3.3 mm (mean value: 3.1 ± 0.1 mm); holotype: 3.0 mm.

Description of larva. Instar I ( Figs 6–18 ). Body subcylindrical, narrowing towards abdominal apex. Measurements and ratios that characterize the body shape are shown in Table 1 . Body colour predominantly piceous to grey; head capsule with two yellowish maculae mesally; head appendages predominantly creamy white to pale yellow; thoracic and abdominal terga grey; legs predominantly creamy white with some greyish maculae; urogomphus yellow except over proximal 1/3 piceous to grey.

Head. Cephalic capsule ( Figs 6–7 ) subquadrate, about as broad as long; maximum width at about level of primary seta PA6; lateral margin of parietale straight; neck constriction present; occipital suture absent; ecdysial line well marked, coronal line long; occipital foramen broadly emarginate ventrally; frontoclypeus rounded mesally, slightly convex, slightly extending medially beyond level of lateral lobes (= adnasalia of BEUTEL 1994); dorsal surface with two egg bursters (= ruptor ovi of BERTRAND 1972), less than half as broad basally than maximum width of antennomere 1; apical margin of frontoclypeus with four spatulate setae (= lamellae clypeales of BERTRAND 1972); gular suture visible; ocularium present, with six stemmata subdivided into two vertical series (four stemmata visible dorsally, two ventrally); tentorial pits visible ventrally on each side of middle at about midlength. Antenna ( Figs 8–9 ) elongate, slender, shorter than HW, composed of four antennomeres; A1 and A4 shortest, subequal in length, A2 and A3 subequal in length; A3 with a ventroapical spinula; lateral elongation of antennomere 3 (A3’) short and bulge-like. Mandible ( Fig. 10 ) prominent, falciform, longer than broad, distal half projected inwards, apex sharp; mandibular channel present, mesal groove enclosed by two shortly serrate edges; pubescence absent from ventral inner margin. Maxilla ( Figs 11–12 ): cardo small, subovate; stipes short and thick, with minute spinulae along inner margin proximad to galea; galea well developed, subconical; lacinia absent; palpifer short, palpomere-like; palpus elongate, three-segmented, shorter than antenna; MP3 slightly longer than MP2, each longer than MP1. Labium: prementum subrectangular, broader than long; palpus elongate, two-segmented ( Fig. 13 ), subequal to maxillary palpus in length; LP2 subequal in length to LP1.

Thorax. Pronotum trapezoidal dorsally, ovate laterally, shorter than meso- and metanotum combined; meso- and metanotum subequal, with anterotransverse carina; sagittal line visible on three tergites; thoracic sterna membranous; spiracles absent. Legs ( Figs 14–15 ) well developed, robust, composed of six articles (including pretarsus), L3 longest, slightly longer than L1 and L2; CO robust, elongate, TR divided into two parts, trochanteral annulus present; FE, TI and TA slender, subcylindrical; PT with two short and slightly curved claws, posterior claw shorter than anterior claw on L1 and L2, claws subequal in length on L3; ventral margin of protibia and protarsus with elongate spinulae; marginal spinulae more faintly developed on mesotibia and mesotarsus, lacking on L3; comb-like spinulae broadly developed anteroventrodistally on protibia and protarsus.

Abdomen ( Figs 16–17 ) eight-segmented; segments I– VI sclerotized dorsally, membranous ventrally, segment VII with ventral plate distinct from tergite, segment VIII (= LAS) completely sclerotized; all tergites with anterotransverse carina; spiracular openings absent; LAS longest, shortly extended posteriorly, convex medially. Urogomphus ( Fig. 18 ) two-segmented; U1 longer than LAS, much longer than U2.

Chaetotaxy ( Figs 6–18 ). Similar to that of generalized Agabinae larva ( ALARIE 1995, 1998) except for following features: seta FR5 close to pore FRd; pore ANi minute; A4 with a minute dorso-apical additional pore; pore MXa absent; setae LA10 and LA12 articulated submedially; FE with one anteroventral, one anterodistal and one posteroventral additional setae; seta FE1 inserted proximally; seta FE6 hair-like; seta AB8 minute; despite thorough effort seta AB14 not found on the only specimen available for study; setae UR2, UR3 and UR4 articulated at about mid-length on U1; pore URc located far from apex of U1; U2 with one minute additional seta proximally.

Instar II. As first-instar larva except for the following features: Measurements and ratios that characterize the body shape are shown in Table 1 . Head appendages yellowish; legs predominantly yellow to pale brown; urogomphus darker, yellow distally.

Head. Frontoclypeus lacking egg-bursters; apical margin of frontoclypeus with 19 spatulate setae. Antenna with A4 shorter than A1. Maxilla with MP2 subequal to slightly longer than MP1. Labium with LP2 slightly shorter than LP1.

Thorax. L3 longer than L1 and L2.

Abdomen: Segment VII completely sclerotized; siphon slightly emarginated apically; U2 much reduced, considerably shorter than U1.

Chaetotaxy. Cephalic capsule with numerous mostly minute secondary setae; parietale with 6–7 spine-like secondary setae on lateral margin and ventral surface; MN with several minute secondary seta along outer margin, proximal to pore MNa; thoracic tergites with numerous minute and hair-like secondary setae; secondary leg setation detailed in Table 2 ; CO with 1–2 secondary pores on posterior surface; TR with one secondary pore on proximal portion; LAS with numerous secondary setae, most of them spine-like.

Instar III ( Figs 3 , 19–23 ).As second-instar larva except for the following features: Measurements and ratios that characterize the body shape are shown in Table 1 . Colour darker; head capsule with one yellow macula around ocularium and another one mesally on frontoclypeus; coxae grey to black over proximal half.

Head ( Fig. 19 ). Apical margin of frontoclypeus with 27–32 spatulate setae. Antenna with A3 shorter than A2. Maxilla with MP2 subequal to slightly shorter than MP1.

Thorax. Spiracles present on mesothorax.

Abdomen ( Fig. 20 ). Spiracles present on segments I–VII.

Chaetotaxy. Cephalic capsule with 7–8 spine-like secondary setae on lateral margin and ventral surface of parietale; mandible with several minute secondary setae along outer margin ( Fig. 21 ); secondary leg setation detailed in Table 2 and illustrated in Figs 22–23 .

Differential diagnosis. The new species can be easily recognized from any Asian Platynectes by dorsally strongly convex habitus, distinctly impressed double reticulation of elytra, and short appendages. In dorsal surface colouration, P. davidorum sp. nov. is similar to P. babai Satô, 1982 from Taiwan and P. hainanensis Nilsson, 1998 from Hainan; however, in addition to characters mentioned above, it is smaller and more roundish. Finally, the new species can readily be distinguished by the shape of median lobe of aedeagus (cf. ŠŤASTNÝ 2003).

In regard to their first instar larva, Platynectes davidorum sp. nov. differs from that of P. curtulus (the only other Platynectes known as first instar) by the following combination of characters: (i) smaller size (HL <0.6 mm compared to 0.8 mm), (ii) presence of four lamellae clypeales (compared to 10) ( Fig. 6 ), (iii) absence of PV additional setae on femur ( Fig. 15 ), (iv) absence of additional setae on the LAS ( Figs 16–17 ) and (v) the non emarginate posterior margin of the LAS (= siphon) ( Fig. 16 ).

As for the second- and third instar larvae, both Platynectes davidorum sp. nov. and P. curtulus can readily be distinguished from P. decemnotatus by (i) absence of secondary setae on the urogomphus, (ii) a two segmented urogomphus and (iii) the bulge-like appearance of the lateral elongation of the third antennomere (A3’) (compared to finger-like). Larvae of Platynectes davidorum sp. nov. differ from those of P. curtulus by (i) the presence of several tiny secondary setae along the outer margin of the mandible ( Fig. 21 ), a unique feature amongst the known Platynectes larvae, and (ii) the absence of dorsal secondary setae on femora ( Figs 22–23 ).

Etymology. The new species is named in honour of four ‘Davids’: father Armand David (1826–1900), French missionary who collected first reliable material of Chinese beetles; David Sharp (1840–1922), British entomologist who produced a monograph on Dytiscidae and described numerous new taxa from China; David Král, our friend and well known specialist on Scarabaeoidea beetles, who devised the trip to Wuyishan; and last but not least David Hájek, a son of the senior author. The name is a noun in plural genitive case.

Collecting circumstances. At the type locality, all adult specimens but one, and all larvae, were collected at night in water film on rock surface of the small cliff ( Figs 24–26 ). One specimen of P. dissimilis , a species common in small streams at the locality, was collected together with specimens of P. davidorum sp. nov. One female specimen of the new species was collected at light trap.

Distribution. The new species is known so far from two localities in Fujian and Zhejiang Provinces, eastern China, ca. 340 km apart.

Figures

Figs 2–5. Platynectes davidorum sp. nov. 2 – habitus of ♁ paratype (5.1 mm); 3 – 3rd instar larva (6.6 mm); 4 – median lobe of aedeagus in lateral view; 5 – parameres. Scale bar = 0.5 mm (Figs 4–5).

Figs 6–13. Platynectes davidorum sp. nov., 1st instar larva. 6 – head capsule, dorsal aspect; 7 – head capsule, ventral aspect; 8 – antenna, dorsal aspect; 9 – antenna, ventral aspect; 10 – mandible, dorsal aspect; 11 – maxilla, dorsal aspect; 12 – maxilla, ventral aspect; 13 – labial palp; dorsal aspect.Abbreviations: EB – egg bursters; FR – frontoclypeus; LC – lamellae clypeales; PA – parietale; sp – spinula, TP – tentorial pits. Numbers and lowercase letters refer to primary setae and pores, respectively. Scale bar = 0.1 mm.

Figs 14–23. Platynectes davidorum sp. nov., 1st instar larva (Figs 14–18) and 3rd instar larva (Figs 19–23). 14 – metathoracic leg, anterior surface; 15 – metathoracic leg, posterior surface; 16 – abdominal segment VIII, dorsal aspect; 17 – abdominal segment VIII, ventral aspect; 18 – urogomphus, dorsal aspect; 19 – head capsule, dorsal aspect; 20 – abdominal segment VIII, dorsal aspect; 21 – mandible, dorsal aspect; 22 – metathoracic leg, anterior surface; 23 – metathoracic leg, posterior surface. Abbreviations: CO – coxa; FE – femur; TA – tarsus; PT – pretarsus; TI – tibia; TR – trochanter. Numbers and lowercase letters refer to primary setae and pores, respectively. * = additional (Figs 14–15, 18) or secondary (Figs 22–23) sensilla. Scale bars = 0.1 mm (Figs 14–18) and 0.5 mm (Figs 19–23).

Figs 24–26. Type locality of Platynectes davidorum sp. nov. 24 – general view of the habitat; 25 – detail of the microhabitat; 26 – P. davidorum sp. nov. in water film on rock surface (photo Yandong Chen).