Chimerogyrus, 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 : 1240-1242

CHIMEROGYRUS GEN. NOV.

lsid: urn:lsid:zoobank.org:act:D7259533-80FC-44A2-B58B-FEDE654E53A5

Type species: Chimerogyrus gigagalea , by current designation, monotypic.

Etymology

The genus name is Latinized from the Greek χιμαιρα, chimaira, a chimera, the amalgamate monster of legend, here in reference to the strange combination of ancestral and derived features of the larval taxon being described, and γύρος, gyros, meaning turning or spinning, a common ending used in gyrinid names..

Diagnosis

Chimerogyrus can be diagnosed by the following combination of characters: cephalic capsule ( Figs 3, 7C, D) not constricted at level of occipital region; FR ( Fig. 3A) symmetrica,l with four equally sized, well-developed teeth; tormae absent; maxilla ( Fig. 4C, D) with elongate cardo and stipes; galea longer than lacinia; lacinia small and strongly curved, with inner margin straight apically and weakly dentate basally, apex without indentation; two long setae ( MX 5 and MX 6) subequal in length at base of lacinia; anterior face of CO ( Fig. 5A, B) with three large, stout, spine-like setae ( CO 6, CO 8 and CO 9); TA 1 long and spine like, situated at mid-length dorsally ( Fig. 5A); pretarsal claws ( Fig. 5A–E) without spinulae; tracheal gills with spinulae; segment X ( Fig. 5F, G) with two long, hair-like setae, spinulae absent; terminal hooks ( Fig. 5F–H) asymmetrical, with lateral hooks narrower and elongate, medial hooks broader, less strongly curved.

The form of the maxilla ( Fig. 4C, D) distinguishes Chimerogyrus from all known gyrinid genera.The maxilla of Chimerogyrus is most similar to that of genera of the tribes Dineutini and Orectochilini, having an elongate cardo that does not cover the ventral joint of the mandible, with the internal margin of the stipes lacking small hook-like setae dorsally. However, the stipes is longer than that of any currently known dineutine or orectochiline larva, which have relatively short stipes ( Figs 1A–D, 2). Furthermore, its maxilla is unlike any known gyrinid larva in that the galea is considerably longer than the small lacinia, rather than being roughly similar in size (as in Dineutus Macleay, 1825 ; Fig. 1B) or smaller in size, as in most genera. The form of the lacinia ( Fig. 4C) is also unique, being strongly curved, with a straight inner margin apically, becoming dentate proximally and possessing two long setae basally. The presence of two long setae of subequal length basal to the lacinia is similar to larvae of the Orectochilini ( Fig. 2), but unlike these genera the lacinia is short, somewhat similar to the Gyrinini , but much narrower and more hook shaped. It can be distinguished from the extinct genus Cretogyrus by having a cephalic capsule without a constriction of the occipital region, four equally sized frontal teeth, the short coronal suture, and by the form of the maxilla.

The setation of the coxae also distinguishes Chimerogyrus from all currently known gyrinid larvae. Chimerogyrus has a series of large, stout, spine-like setae ( CO 6, CO 8 and CO 9) distomedially on the anterior surface of the CO.