Polynoncus galapagoensis ( Van Dyke, 1953 )

Costa-Silva, Vinícius, Strümpher, Werner P., Thyssen, Patricia J. & Vaz-de-Mello, Fernando Z., 2024, Taxonomic revision of the South American genus Polynoncus Burmeister, 1876 (Coleoptera: Scarabaeoidea: Trogidae), Journal of Natural History 58 (1 - 4), pp. 14-166 : 78-80

Polynoncus galapagoensis ( Van Dyke, 1953)

( Figures 29–30 )

Trox galapagoensis Van Dyke, 1953: 124 (original description); Vaurie 1962: 131 (redescription); Linsley and Usinger 1966: 152 (list of Galapagos species); Franz 1985: 96 (list of Galapagos species)

Trox (Polynoncus) galapagoensis : Scholtz 1982: 16 (catalogue)

Polynoncus galapagoensis : Scholtz 1986a: 362 (systematics); Scholtz 1990: 1447 (redescription); Zidek 2013: 10 (checklist); Zidek 2017: 101 (checklist)

Type specimen examined (through detailed photographs). HOLOTYPE. (♀ CASC – Figure 29 ) First label [white, aged, with the right wing glued]: ‘ R.L. wing’. Second label [white, aged, typeset]: ‘ Culpepper I. / Galapagos Is. / IX – 05’. Third label [white, aged, typeset]:‘ Coll. By / F.X. Williams’. Fourth label [red, E.C. Van Dyke’s handwriting]: ‘ Trox / galapagoensis / HOLOTYPE [typeset] / E.C. Van Dyke’. Fifth label [white, typeset]: ‘ ♀ ’. Sixth label [white, aged, with black border]:‘ Trox / galapagoensis / Van Dyke’ . Seventh label [white, typeset]:‘ California Academy / of Sciences / Type 7409 [handwritten] / No’ . ( Figure 29c ). Type locality: ‘ Culpepper I. [Island]’ (currently named Darwin Island), Galápagos Archipelago .

Differential diagnosis. This rare wingless species is known only from the Galapagos Islands. It is similar to Polynoncus seymourensis ( Van Dyke, 1953) , the only other species of Polynoncus occurring on the islands. Polynoncus galapagoensis differs from the latter in that the humeral calli are obsolete and the elytral tubercles are round and contiguous, forming distinct ridges over the length of elytra. The humeral calli are present in Polynoncus seymourensis (fully winged) and the elytral tubercles seldom form continuous ridges.

Geographic distribution. Polynoncus galapagoensis is endemic to the Galapagos Islands ( Figure 30 ). Vaurie (1962) mentioned a single record of P. galapagoensis from Wenman (Wolf) Island based on one elytron examined. Later, Scholtz (1990) recorded 19 additional specimens from Culpepper Island . Apart from the type specimen (from Culpepper [Darwin] Island), no other specimen was examined by us.

Figures

Figure 29. Holotype of Trox galapagoensis Van Dyke, 1953 (now Polynoncus galapagoensis): habitus in a, dorsal and b, lateral view; c, right wing and labels. Photos by Rachael Diaz-Bastin (CASC).

Figure 30. Distribution map of Polynoncus galapagoensis (red circle) and P. seymourensis (green triangles) in Galapagos Islands, South America. The records with a black dot in the centre indicate the type locality of the respective species.