Platynus Bonelli, 1810

Liebherr, James K. & Ivie, Michael A., 2021, Two New Platynus Bonelli (Coleoptera: Carabidae: Platynini) from Nevis and St. Kitts, Lesser Antilles, The Coleopterists Bulletin 75 (1), pp. 59-74 : 61-62

Genus Platynus Bonelli, 1810

Assignment of species to the various genera of the tribe Platynini has been historically fluid. Given the tribe’ s worldwide distribution and its high diversity in montane subtropical and tropical regions ( Basilewsky 1985; Moret 1999; Whitehead 1973), the assignment of newly discovered species to genera has been largely based on regional taxonomic treatises. For the Neotropics, Moret (1999) provided criteria for distinguishing several subsidiary lineages from the more generalized ground-plan characterizing species assigned to the tribal type genus Platynus Bonelli, 1810 . The species described here fall into one of those lineages— Dyscolus Dejean, 1831 —with Dyscolus memnonius Dejean of Basse-Terre, Guadeloupe, the type species for that genus ( Chaudoir 1878). Moret extensively treated the South American platynine fauna, combining species with Dyscolus based on the setation and lobate condition of the fourth metatarsomere ( Moret 1996). Relative to Dyscolus in the sense of Moret, Platynus species exhibit only a slight emargination of metatarsomere 4, and a single longitudinal row of simple setae each side of the tarsomere’ s ventral surface. Thus, Dyscolus can be defined synapomorphically; however, its recognition renders Platynus defined solely by symplesiomorphies.

More recently it has been shown that species within the Platynus generic complex may differ in the fundamental organization of the male reproductive organs. In the generalized, plesiomorphic condition, male beetles retain two testes, one each on the right and left, whereas other lineages exhibit loss of the left testis coupled with hypertrophy of the accessory glands associated with the remaining right testis ( Will et al. 2005). Among taxa studied across the tribe Platynini , the plesiomorphic, bilateral testis configuration occurs in the following genera represented in the New World: Agonum Bonelli , Anchomenus Bonelli , Atranus LeConte , Glyptolenus Bates , Incagonum Liebherr , Olisthopus Dejean , Paranchus Lindroth , Rhadine LeConte , Sericoda Kirby , and Tanystoma Motschulsky.Among various species traditionally treated as Platynus (e.g., Lindroth 1966), either the single testis or bilateral testis configuration may occur. Two testes are observed in Platynus assimilis (Paykull) [the Palearctic type species of Platynus Bonelli ( Bousquet 2003, 2012; Bousquet and Larochelle 1993; Lorenz 2005b; but see the invalid proposal of Schmidt 2000, 2018)], and in the Nearctic taxa Platynus decentis (Say) , Platynus indecentis Liebherr and Will ( Liebherr and Will 1996), and five species of Platynus subgenus Batenus Motschulsky ( Liebherr 1989) . The single testis condition is present in all other United States Platynus species examined— Platynus brunneomarginatus (Mannerheim) , Platynus opaculus LeConte , Platynus ovipennis (Mannerheim) , Platynus parmarginatus Hamilton , Platynus tenuicollis (LeConte) , and Platynus trifoveolatus Beutenmüller —as well as: 1) the Mexican species Platynus (Dyscolus) segregatus (Bates) , Platynus (Glyptolenopsis) marginissimus Liebherr , Platynus (Scaphiodactylus) modestus (Dejean) , and Platynus (Stenocnemion) acuminatus (Chevrolat) ; 2) the Lesser Antillean Platynus (Dyscolus) paramemnonius Liebherr from Dominica; and 3) the Hispaniolan Platynus (Dyscolus) biramosus (Darlington) and Platynus (Glyptolenopsis) metallosomus Liebherr ( Will et al. 2005; Liebherr, unpublished data). A comprehensive phylogenetic analysis of Platynus and the numerous subgeneric or generic-level entities closely associated with that name does not exist, but paraphyly of the nominate subgenus Platynus relative to the other named putatively monorchid lineages is strongly suggested based on cladistic interpretation of this dramatic synapomorphy.

For purposes of this contribution, we have chosen to recognize Dyscolus monophyly while recognizing that the final apportionment of lineages within a broadly-based, plesiomorphically defined assemblage of genera also including Platynus has yet to be done. We use Platynus as the genus to combine presently with these species, with Dyscolus used for subgeneric placement in order to recognize the monophyletic relationship of the new species to the demonstrably monorchid Dyscolus taxa from South and Central America ( Camero Rubio 2010; Moret 1989, 1990a, b, 1993, 1994; Moret and Casale 1998). By extension, other monorchid taxa combined with Glyptolenopsis Perrault, Scaphiodactylus Chaudoir, and Stenocnemion Moret ( Will et al. 2005) would share this synapomorphy. This classificatory solution allows recognition of both names— Platynus and Dyscolus —while calling for a comprehensive analysis of at least all New World lineages of single testis taxa and their phylogenetically related, plesiomorphic two-testis relatives.

Species described below are diagnosable as Platynus based on the characters presented in Liebherr (1987: 292–296). All taxa thus far placed in the Lesser Antillean P. memnonius species-group ( Liebherr 1987) are representatives of subgenus Dyscolus based on the conjunction of several criteria. Firstly, the type species of Dyscolus is P. (D.) memnonius of Basse-Terre. Secondly, the Lesser Antillean and South American Dyscolus share a very similar female reproductive tract, with a bursa copulatrix basally bordered by a broad microtrichial band, and a spermatheca with a short duct ( Figs. 14–15 ; Moret 1999: fig. 14). Also, the Lesser Antillean and South American Dyscolus all exhibit apically emarginate fourth metatarsomeres, with the outer apical lobe longer than the median length, and the tarsomere’ s ventral surface densely setose laterally.

Figures

Figs. 10–15. Platynus species, reproductive structures. Male genitalic structures: 10) P. racquelae, new species, male paratype (WIBF) aedeagal median lobe, right lateral view; 11) P. racquelae, new species, male terminal abdominal segments VIII and IX; 12) P. luciae, male aedeagal median lobe, right lateral view; 13) P. luciae, male terminal segments VIII and IX. Abbreviations for male structures include: is, internal sac of median lobe, partially everted; lp, left paramere; rp, right paramere; sc, sagittal crest of median lobe; VIII, internal apodeme of laterotergites, segment VIII; IX, internal apodeme of laterotergites, segment IX. Female reproductive tract, ventral view: 14) P. racquelae, new species, female paratype (CUIC); 15) P. luciae (CUIC). Abbreviations for female structures include: bc, bursa copulatrix; co, common oviduct; gc1, basal gonocoxite 1; gc2, apical gonocoxite 2; hg, hindgut; lo, lateral oviduct; mb, microtrichial band; sd, spermathecal duct; sg, spermathecal gland; sp, spermatheca; v, vagina; vll, vagina lateral lobes.