Chimerogyrus gigagalea, Gustafson & Michat & Balke, 2020

Gustafson, Grey T., Michat, Mariano C. & Balke, Michael, 2020, Burmese amber reveals a new stem lineage of whirligig beetle (Coleoptera: Gyrinidae) based on the larval stage, Zoological Journal of the Linnean Society 189, pp. 1232-1248 : 1242-1243

CHIMEROGYRUS GIGAGALEA SP. NOV.

lsid: urn:lsid:zoobank.org:act:0B604A53-EED0-4CD1-9478-40C609EFE8A

Type locality: Myanmar, Kachin State, Hukawng valley near Tanai .

Type material: Single Burmese amber piece, deposited in ZSMG.

Etymology

The specific epithet is a combination of the Greek γίγας, gigas, giant, and Latin galea, an anatomical structure, in reference to the large galea of the new taxon. It is a noun in apposition.

Description

Body ( Fig. 7A, B): Elongate, parallel sided; head and pronotum strongly sclerotized, remainder of thorax and abdomen weakly sclerotized. Body size: L = 11.5 mm, W = 1.0 mm.

Head: Cephalic capsule ( Figs 3, 7C, D): subrectangular, lateral margins slightly longer than anterior and posterior margins, without constriction of occipital region; occipital foramen dorsally with narrow margin; occipital suture absent; coronal suture short; frontal sutures U-shaped, extending to antennal bases; frontoclypeus roughly subtriangular, anterior margin divided into three lobes, medial lobe symmetrical, with four equally sized, well-developed teeth; tormae absent; lateral lobes well developed, not projecting anteriorly beyond medial lobe; PA with six stemmata at each side, four situated dorsally, two ventrally. Antenna ( Fig. 4A): elongate and slender; composed of four antennomeres, with I shortest and round; II and III longest, subequal in length, with II cylindrical and straight, III weakly curved; IV shorter, ~3× length of I, weakly curved. Mandible ( Fig. 4B): relatively elongate, curved inward; broadest basally and gradually attenuated apically, ending in sharp apex; inner margin smooth, without denticles or teeth; retinaculum absent. Maxilla ( Figs 4C, D): well developed, not covering ventral mandibular joint; cardo elongate, subrectangular; stipes long, subtrapezoidal, bearing a lacinia and galea on distal inner margin, distal outer margin with palpifer; dorsally without series of small hook-like setae on internal margin; lacinia relatively small and strongly curved, with sharp apex; posterior margin straight in apical half, dentate basally; galea longer than lacinia, two-segmented, basal segment short and broader, apical segment elongate, tapered towards apex, ~2.5× length of basal segment; palpifer short, palpomerelike in form; maxillary palp elongate and narrow, composed of three palpomeres; I shortest, III longest. Labium ( Fig. 4E, F): well developed; prementum divided longitudinally into two subcylindrical halves fused basally; labial palps elongate and narrow, two-segmented; segments I and II nearly equal in length.

Thorax: Pronotum slightly larger than subequal meso- and metanotum; protergite well developed, dorsally covering entire segment, with straight anterior margin, rounded lateral and posterior margins, sagittal line evident; membrane separating pro- and mesonotum, with narrow sclerite possessing rounded posterior margin and sagittal line. Legs ( Fig. 5A–E): long, slender, composed of six segments; L3 longest, L1 shortest; CO ovoid, robust, TR short, FE relatively broad, TI narrower, TA narrowest and subcylindrical in form, PT with two long, slender, weakly curved pretarsal claws, posterior claw shorter than anterior claw; spinulae absent.

Abdomen: Ten-segmented, with segments I – VIII similar in form, bearing a tracheal gill at posterolateral angle; segment IX with two tracheal gills at posterolateral angle; segment I similar in size to metanotum; segments II–VII larger and similar in size; segments VIII–IX gradually becoming smaller; tracheal gills slender, plumose with spinulae on anterior and posterior surfaces; gill of segment I smallest, gills of segments II–V larger and similar in size, gills of segments VI–IX becoming gradually larger posteriorly, with gills of segment IX largest; segment X small and narrow, arising from posteroventral face of segment IX, without tracheal gills and ventral spinulae, bearing four strongly sclerotized terminal hooks; lateral hooks narrower and more elongate, medial hooks broader and less elongate.

Chaetotaxy: Frontoclypeus: numerous short, hair-like setae posteriorly. Parietal: basal half with one long hair-like seta ( PA 6) evident dorsally. Maxilla ( Fig. 4C): base of lacinia bearing two straight hair-like setae of subequal length, anterior ( MX 5) longer than posterior ( MX 6). Legs ( Fig. 5A–E): anterior face of CO with three large, stout, spine-like setae ( CO 6, CO 8 and CO 9) situated distomedially and one small hair-like seta ( CO 10) distoventrally; posterior face proximally with one hair-like seta ( CO 12) and two hair-like setae ( CO 11 and one probably additional or secondary seta) distally; anterior face of TR with one short hair-like seta ( TR 3) and one long hair-like seta ( TR 4) ventrodistally; posterior face of TR with one short hair-like seta ( TR 5) ventrodistally; anterior face of FE distally with two short spine-like setae, one ( FE 2) dorsally and another ( FE 3) ventrally; posterior face of FE distally with one longer spine-like seta ( FE 4) and two small spine-like setae ( FE 5 and FE 6); anterior face of TI with one long hair-like seta ( TI 1) proximally and three short spine-like setae distally ( TI 2, TI 3 and TI 4); posterior face of TI distally with one long spine-like seta ( TI 5) and two short spine-like setae ( TI 6 and TI 7); anterior face of TA with one long spine-like seta at mid-length dorsally ( TA 1) and two short spine-like setae distally ( TI 2 and TI 4); posterior face of TA with two short setae distally ( TA 5 and TA 6); anterior face of PT with one short spine-like seta on basoventral portion ( PT 1). Abdomen ( Fig. 5F, G): segment X with two long hair-like setae paramedially.

Differential diagnosis

The genus is monotypic. The generic diagnosis provided above separates the species from all other known species based on larvae.