Heterogyrus milloti Legros, 1953

Gustafson, Grey T., Bergsten, Johannes, Ranarilalatiana, Tolotra, Randriamihaja, Jacquelin Herisahala & Miller, Kelly B., 2017, The Morphology and Behavior of the Endemic Malagasy Whirligig Beetle Heterogyrus milloti Legros, 1953 (Coleoptera: Gyrinidae: Heterogyrinae), The Coleopterists Bulletin 71 (2), pp. 315-328 : 317-321

Heterogyrus milloti Legros, 1953

Material Examined. MADAGASCAR: Fianarantsoa Province: 7 km W Ranomafana , 1,100 m, 8-21.x.1988, leg. W. E. Steiner (3 ex. MSBA) ; same as previous except 1,000 m, 1-7. iii.1990 (3 ex. MSBA) ; ~ 8 km W Ranomafana town , stream, 21°14.992’S, 47°24.332’E, 20. xi.2008, leg. K. B. Miller, KBM20110801 (18 ex. MSBA) ; Ranomafana NP , 3.8 km SE of Vohiparara village , 21.2498°S, 47.4041°E, 1,080 m, 2.xi.2014, forest stream by road, leg. G. Gustafson GTG110214D (6 ex. GTGC) . Ranomafana NP , 3.8 km SE of Vohiparara village , 21.2498°S, 47.4041°E, 1,080 m, 2.xi.2014, forest stream by road, Leg. J. Bergsten, T. Ranarilalatiana & S. Holmgren, MAD14-08, NHRS- JLKB000027148 (3 ex. NHRS) ; Ranomafana NP , 3.8 km SE of Vohiparara village, 21.2498°S, 47.4041°E, 1,080 m, 1.xi.2011, small forest stream with pools, leg. J. Bergsten, R. Bukontaite, T. Ranarilalatiana & J. H. Randriamihaja, MAD11-11, NHRS-JLKB000027145 (20 ex. NHRS, 4 ex. DEUA); Ranomafana NP, 500m from Micet station by the road, 21.2552°S, 47.41214°E, 960 m, 30. x.2011, small forest stream with sidepools, leg. J. Bergsten, R. Bukontaite, T. Ranarilalatiana & J. H. Randriamihaja, MAD11-01, NHRS-JLKB000027144 (8 ex. NHRS) ; Ihorombe, R. S. Pic d’ Ivohibe corridor: Ampanasaha : at the east limit of the corridor, close to Ampanasaha river : 22.47185°S, 46.957783°E, 926 m, 9.xii.2013, weakly trickling forest stream with dead leaves, MAD13-52, leg. J. H. Randriamihaja & T. Ranarilalatiana NHRS-JLKB000027147 (1 ex. NHRS) ; Ihorombe, R. S. Pic d’ Ivohibe : Ampanasaha : stream before river Ampanasaha : 22.475516°S, 46.95273°E, 1,006 m, 8.xii.2013, small stream with pools on rocks, MAD13-50, leg. J. H. Randriamihaja & T. Ranarilalatiana NHRS-JLKB000027146 (5 ex. NHRS) .

Type Locality. Ampasy , upper Iantara valley, southeast of Andringitra massif, Fianarantsoa, Madagascar ( Viette 1991). This is located in or just outside the southeastern corner of Andringitra National Park (approximate coordinates 22.3°S, 47.02°E) .

Diagnosis. Heterogyrus milloti is recognized by the following unique combination of character states: Antennal flagellum 9-segmented, strongly setose with long setae present along anteromedial face of flagellomeres II–IX; eyes widely separated dorsoventrally by well-developed interorbital region, interorbital region with antennal groove; labrum transversely divided by strong infolding with setose anterior margin; maxillary galea 2-segmented; mentum trilobate; prementum not fused to mentum; pronotum with median lobe projecting onto head capsule; lateral margins of pronotum and elytra broad, explanate, setose; scutellar shield visible with elytra closed; elytron with sutural border and nine serial striae, yellow and black striped in coloration; protibial medial spur present; metaventrite with triangular lateral wings, metaventral discrimen with short transverse suture; metacoxae oblique; abdominal sternite VIII trilobate in males, bifid in females.

Redescription. Size: ³ length 6.0– 6.5 mm, width 3.0– 3.5 mm; ♀ length 5.7–6.0 mm, width 3 mm. Habitus: Medium size; body elongate oval, weakly attenuated posteriorly; in lateral view, strongly dorsoventrally depressed, slightly humped posteriad to scutellar region. Coloration: Head with vertex bronzy green medially, posteriorly near pronotum and ocular region black; frons laterally bronzy green, becoming more golden bronzed medially, frontolateral margins black; clypeus yellow; labrum dorsally black, yellow beneath fringe of setae; antennal scape, pedicel, and first flagellomere yellow, remaining flagellomeres black; pronotum medially golden yellow, posterior margin black, pale yellow lateral margins with black border; elytral suture and striae lined in black, black stripes present on intervals II, IV, VI, and VIII at least posteriorly, remainder of elytra yellow, elytral lateral margin pale yellow with black border, elytral apex including margin black; scutellar shield anteromedially reddish orange, black laterally and apically; protarsal claws red; venter overall light yellowish orange, propleuron and epipleuron paler yellow in color, ventral eye ocular region black, abdominal tergites brownish orange. Head: Vertex with well impressed reticulation composed of round, irregular sculpticells, sparse, weakly impressed, nearly imperceptible punctation present; dorsal eye with thick, raised margin, eyes widely dorsoventrally separated with well-developed interorbital region; interorbital region with antennal groove, setae present medially dorsad and ventrad to groove; frons with similar reticulation and punctation as vertex, frontolateral margin with welldeveloped bead ( Fig. 2A, B ), lightly wrinkled; frontoclypeal suture well developed, crescentshaped; clypeus with lightly impressed reticulation composed of polygonal sculpticells, weak punctation present, most evident at anterior margin, punctures separated by ca. 2–3X diameter of single puncture; clypealia elongate, extending well onto posterolateral corners of labrum, setose; antennal scape cup-shaped; pedicel triangular in shape; flagellum with 9 flagellomeres ( Fig. 3A ), flagellomeres II–IX with long, yellow setae on anterior face, V–IX setose with smaller, finer setae, ultimate flagellomere nearly entirely covered with setae ( Fig. 3B ); labrum strongly transverse, basally divided by strong, transverse infolding ( Fig. 1A ), fold lined with long, gold setae, dorsad of fold reticulation composed of round, polygonal sculpticells, posteriorly with long, yellow setae present in recessed punctures, ventrad of fold without reticulation or punctation, ventral margin of labrum lined with setae; maxilla with 2-segmented galea; lacinia narrow and arcuate in form, with 2 patches of setae present on medial surface; maxillary palp 4-segmented with ultimate segment ca. 3X length of penultimate; labial palp elongate and narrow, 3-segmented with ultimate and penultimate palpomeres similar in length, both at least 2X length of segment I, apical palpomere weakly curved; palpigers fused medially, prementum distinctly separated from mentum by membranous area ( Fig. 2C, D ); mentum trilobate with lateral lobes 2X length of medial lobe, medial lobe margined anteriorly ( Fig. 2D ); gula broad and trapezoidal, gular suture present and well developed, reaching anterior margin, narrow sulcus present medially. Thorax: Pronotum with strong medial lobe extended onto head capsule as far as posterior 1/3 of dorsal eye ( Fig. 2B ), medially weakly sinuate; pronotal disc with reticulation composed of polygonal sculpticells, with weakly impressed punctation separated by 0.67X diameter of single puncture; transversly impressed pronotal line briefly evident laterally before joining anterior border ( Fig. 2B ); pronotal setose border present laterally ( Fig. 2B ), width 0.67X diameter of dorsal eye anteriorly, attenuated posteriorly; pronotal lateral margin broad, explanate, setose; prosternum cushion-shaped with medial shallow depression ( Fig. 4 ); notopleural and propleurosternal sutures present, meeting anteriad at anterior border of pronotum, forming very short notosternal suture; propleuron with shallow depression for leg reception; forelegs with protrochanter glabrous; profemur strongly swollen basally, male profemur basally with 2–3 distinct denticles present; basal half of profemur with series of long, fine setae along posterior margin of ventral face; ventral face of profemur apically with depression for reception of protibia; anterior face of profemur with 4 setigerous punctures, short stout setae in recessed pits also present basoposteriorly; protibia narrow, sinuate; apical 1/2 of ventral face setose, setation primarily composed of narrow, yellow setae, longer setae 3X length of shorter abundant setae fairly evenly spaced along setose region, apical margin of ventral protibial face ringed with stout setae; posterior face of protibia with additional line of short, yellow setae, reduced protibial brush present; medial protibial spur present ( Fig. 5C , stb); apicolateral corner of protibial apex with few peg-like setae ( Fig. 5c , lps); protarsus of male with posterior surface covered with narrow, elongate, adhesive setae of uniform type, adhesive setae fused into 5 plates ( Fig. 5A ); lateral and posterior margins of adhesive palette with fringe of long, fine, yellow setae; posterior face of female protarsus covered in yellow setae, anterior face of protarsus of both sexes with protarsomeres I–IV possessing setose patches at distomedial corner; protarsomere V at least 2X size of IV, with small setose patch distomedially; protarsal claws emerging straight in female, at 90° angle in male; scutellar shield transverse, short and triangular, visible with elytra closed; elytron with 9 distinct serial striae ( Fig. 9G ); striae I–VI present as lineate grooves; stria VII composed of faintly impressed punctures; stria VIII present as punctures evident in humeral region, remaining punctures highly reduced, almost imperceptible; stria IX lineate, situated at lateral margin; elytral sutural border present; lateral margin of elytra setose, broad and strongly explanate, ending at elytral apex; mesoventrite triangular and elongate, anteriorly bordered with strong medial projection; mesothoracic discrimen well developed; laterally depressed along with mesanepisternum for foreleg reception, depression running nearly 1/2 mesoventrite length; mesepimeron narrow and strap-like; middle legs with elongate triangular mesocoxa running obliquely, mesocoxal process with paramedial setose patch basally; mesotrochanter short and trapezoidal; mesofemur broad, dorsal margin distally with sparse, long setae; mesotibia broad with distal lateral angle produced, margin with evenly spaced peg-like setae, dorsal margin of posterior face with long natatory setae, distal ventral corner of mesotibia with short series of peg-like setae; 2 mesotibial spurs present, posterior spur over twice as long as anterior spur; mesotarsus elongate, narrow; mesotarsomere I in form of isosceles triangle, proximal dorsal lobe possessing small fringe of natatory setae; II–IV narrow, trapezoidal; V quadrate, dorsally with fringe of natatory setae; all mesotarsomeres ventrodistally with stout spine-like setae; mesotarsal claws small, not sexually dimorphic; metaventrite medially narrow ( Fig. 1B ), diamond-shaped, metaventral discrimen present with short transverse sulcus anteriorly ( Fig. 9F ), lateral wings of metaventrite in form of nearly equilateral triangle, metanepisternum lobiform; hind leg with metacoxae running obliquely ( Fig. 1B ); metacoxal process with shallow punctures, very weakly impressed transverse reticulation, setose patches present paramedially; in lateral view, metacoxal cavity narrowed anteriorly, ventral margin with distinct peg posteriorly ( Fig. 11B ); remainder of hind leg similar in form to middle leg. Abdomen: Dorsally abdominal tergites VI–VIII pigmented and setose, VII and VIII densely covered with long setae; abdominal sternites II + III (ventrite I) 2X size of sternite IV, sternites IV–VII similar in size and form, sternite VIII (ventrite VI) triangular, bifid apically in females, trilobate in males ( Fig. 6A, B ). Genitalia: Aedeagus with median lobe slightly shorter than parameres, evenly narrowed towards apex, with distinct subapical lateral expansion ( Fig. 7 ); in dorsal view, expansion with arcuate grooves ( Fig. 7A ); apex acuminate, flatly rounded; in doesal view, median lobe with 2 paramedial grooves; 1 medial longitudinal list evident; in ventral view, sperm groove narrow, mostly parallel-sided, weakly expanded proximally ( Fig. 7C ); in lateral view, apex dorsally curved ( Fig. 7B ); parameres in dorsal view weakly laterally expanded in apical 1/3, apex obliquely truncate with lateral angle distinct, long setae confined to apex, medially weakly reflexed; in ventral view, basal piece present as distinct sclerite, fused to parameres ( Figs. 7C , 9C, D ), basally with acuminate process directed anteriorly. Female reproductive tract ( Fig. 8 ) with ovoid spermatheca atop 2 strongly sclerotized vshaped ridges; sclerotized v-shaped ridges potentially associated with fertilization duct ( Fig. 8A ); spermatheca subapically with elongate spermathecal duct emergent dorsally, basally with sac-like spermathecal gland also emergent dorsally anteriad to strongly sclerotized dorsal fold ( Fig. 8B ); gonocoxae stout, rectangular, setose ( Fig. 8A ); medial apodeme present; lateral tergites relatively broad, weakly expanded apically.

Sexual Dimorphism. There is sexual size dimorphism with males normally larger than females. The profemora are sexually dimorphic in form with males having the profemur more swollen basally and adorned with three distinct denticles. In females, there is slight indication of the denticles at the base of the profemur, but they are clearly reduced, only evident in the distal one, corresponding to the most strongly produced denticle in the male. The ultimate abdominal ventrite is strongly sexually dimorphic. In females, abdominal sternite VIII is apically bifid, whereas in males it is distinctly trilobate ( Fig. 6B ). The trilobed nature of the male abdominal sternite VIII is proposed to be an intermediate step in a transitional series from the deeply divided abdominal sternite VIII of males of Spanglerogyrus to the undivided sternite VIII of the Gyrininae (see Miller and Bergsten 2012 for more details).

Distribution. This species is known only from a few localities in the mountainous escarpment of southeastern Madagascar, Upper Iantara River valley (southeast of Andringitra massif), Pic d’ Ivohibe Special Reserve (S. R.), and Ranomafana National Park (N. P.).

Habitat. The 2014 specimens were collected in a narrow gully within montane rainforest ( Fig. 10 and Movie 1: www.youtube.com/watch? v=oQAkdGNwhjQ). The gully was choked with debris such as logs, broken branches, and boulders, potentially the result of past flooding. The stream itself was mostly a trickle forming pools and retreating underground at points. Adjacent to the larger pools, the rocks were wet and covered with moss. The larger pools with greater numbers of specimens were often no more than ca. 15 cm deep with sandy bottoms and leaf packs. Individuals could also be found in the dark recesses under overhangs of rocks and logs. Steiner’ s labels give a similar description of the habitat, where in 1988 Heterogyrus was collected: “stream with mossy rocks and sandy bottom, montane rainforest.” A few specimens were collected in 2011 in a similar forest stream crossing the road about 1.7 km southeast of the first locality in Ranomafana N. P., right below the road where the stream runs in a culvert. In 2013, a specimen was collected in a somewhat different habitat in Pic d’ Ivohibe S. R. This locality consisted of a weakly trickling forest floor stream with leaf-choked pools. A few more specimens were found in another nearby stream with rocks and pools. Both streams were found in near pristine humid forest at a similar altitude to the ones in Ranomafana (900–1,000 m).

Figures

Fig. 2. Heterogyrus milloti. A) Head capsule anterior view, scale bar = 500 µm, B) Oblique view of anterior half of body, C) Mentum and prementum, box indicates area shown in D, D) Prementum and medial lobe of mentum.

Fig. 3. Antennae of Heterogyrus milloti and Spanglerogyrus albiventris. A) Antenna of H. milloti, box indicates area shown in B, scale bar = 300 µm, B) Antennal apex of H. milloti, s.b. = sensilla basiconicum type, s.c. = sensilla chaetica type, scale bar = 50 µm, C) Most of antennal flagellum of S. albiventris, scale bar = 100 µm.

Fig. 1. Heterogyrus milloti. A) Dorsal habitus of male, scale bar = 2 mm, B) Ventral habitus, lw = lateral wing of metaventrite, ma = metanepisternum, Roman numerals indicate abdominal sternites.

Fig. 4. Prosternum of Heterogyrus milloti, ventral view, scale bar = 200 µm.

Fig. 5. Heterogyrus milloti. A) Male protarsus, posterior view, box indicates area shown in B, scale bar = 400 µm, B) Adhesive setae, showing fusion of individual adhesive setae into plate, C) Protibial apex, lps = peg-like lateral setae, pts = protibial medial spur, stb = setose brush, scale bar = 300 µm.

Fig. 9. Morphology of Heterogyrus milloti, Spanglerogyrus albiventris, and Gyrinus amazonicus Ochs. A) Aedeagus of S. albiventris, ventral view, box indicates area shown in B, B) Basal piece of S. albiventris, C) Aedeagus of H. milloti, ventral view, box indicates area shown in D, D) Basal piece of H. milloti, E) Most of aedeagus of G. amazonicus, ventral view, bvp = basoventral process, F) metaventrite of H. milloti, showing metaventral discrimen with short transverse sulcus, G) Left elytron of H. milloti, scale bar = 1 mm.

Fig. 11. Metacoxae of Gyrinidae, right lateral view showing metacoxal cavity, boxes indicate focal areas. A) Spanglerogyrus albiventris, B) Heterogyrus milloti, arrow indicates peg, C) Gyrinus sp., D) Gyretes sp.

Fig. 6. Heterogyrus milloti. A) Male abdominal sternite VIII, box indicates area shown in B, scale bar = 500 µm, B) Apex of male abdominal sternite VIII.

Fig. 7. Heterogyrus milloti, aedeagus. A) Dorsal view, B) Lateral view, C) Ventral view. Scale bar = 1 mm.

Fig. 8. Heterogyrus milloti, female reproductive tract. A) Ventral view, B) Lateral view. Scale bar = 0.75 mm.

Fig. 10. Habitat of Heterogyrus milloti. A) Forest stream 3.8 km SE of Vohiparara village, 21.2498°S, 47.4041°E, 1,080 m, Ranomafana National Park, Fianarantsoa, Madagascar, B) Forest stream approximately 8 km E of Ivohibe village, 22.4755°S, 46.953°E, 1,010 m, Ampanasaha, Pic d’Ivohibe Special Reserve, Ihorombe, South of Andringitra N.P. Fianarantsoa, Madagascar.