Arthropeina

Fachin, Diego Aguilar & Amorim, Dalton De Souza, 2014, Taxonomic revision of the Neotropical genus Arthropeina Lindner, 1949 (Diptera: Xylomyidae), Zootaxa 3827 (2), pp. 231-257 : 256

Arthropeina apomorphies

The conical shape of the antenna, with flagellomeres 7 and 8 together, forming a stylus ( Figs. 2–7 ) that is as long as or longer than the remainder of the flagellum has been proposed as synapomorphic for the genus ( Artigas & Papavero, 1991; Woodley, 2011). This differs from the combined length of flagellomeres 7 and 8, which are shorter than the remaining flagellomeres in Solva and do not form a stylus ( Fig. 1 ). In Arthropeina , the flagellomeres differ from each other in size and shape ( Figs. 2–7 ), while in Solva ( Fig. 1 ; Daniels, 1976, fig. 3) most flagellomeres are similar in size and shape (except for flagellomere 8 which is slightly narrowed towards apex). This is another feature that may be synapomorphic for Arthropeina . A more detailed comparison between additional species of Solva and other xylomyids would make this statement more robust.

Papavero & Artigas (1991) proposed that the spermathecal capsule formed by three “layers” or coils—based only on their examination of Arthropeina fulva —is apormophic in species of the genus. This condition is actually shown here to be autapomorphic for A. pseudofulva ( Fig. 53 ), while A. fulva has the spermatheca formed by two coils ( Fig. 18 ). The coiled spermathecal capsule, as described by Papavero & Artigas (1971) (independently of the number of coils), seems to be a synapomorphy for a small clade within Arthropeina including A. fulva , A. colombiana and A. pseudofulva . The “remnant of middle spermathecal duct” ( Papavero & Artigas, 1991) certainly corresponds to the spermathecal duct (e.g., Fig. 56 ) cut during preparation, as already stated by Woodley (2011: 422). The statement that the valves of the spermathecal ducts ( Papavero & Artigas, 1991) are an apomorphic condition in the genus, hence, as commented by Woodley (2011), is not confirmed. Other dipteran families also have this condition (see e.g., Artigas, 1971). A wider comparison with other groups of lower brachycerans would be necessary to properly establish the level of origin of this feature—a single origin with losses or independent origins in different families. Additionally, the genital fork in Arthropeina presents a unique condition in Xylomyidae at the level of current knowledge, the membranous lobes (e.g., Fig. 21 ), not found in other xylomyid genera.

A careful morphological study of Solva species would certainly help to better understand of the evolution of features varying within Arthropeina and furnish important evidence towards the construction of a detailed phylogenetic study of the family.

Figures

FIGURES 1 – 7. Antennae of Xylomyidae species. 1. Solva sp., female. 2. Arthropeina fulva. 3. A. colombiana, sp. nov., female holotype. 4. A. diadelothorax, sp. nov., holotype. 5. A. lindneri, sp. nov., paratype. 6. A. melanochroma, sp. nov., female paratype. 7. A. pseudofulva, sp. nov., paratype. Abbreviations: flgm, flagellomere; ped, pedicel; scp, scape.

FIGURES 50 – 55. Arthropeina pseudofulva, sp. nov., paratype. 50. Genital fork, ventral view. 51. Genital fork, lateral view. 52. Genital fork, dorsal view. 53. Spermatheca. 54. Sternite 8, dorsal view. 55. Female genitalia, dorsal view. Abbreviations: cerc, cercus; go, genital opening; ml, membranous lobe; pp, posterolateral process; ppm, projection of posterior margin; st, sternite; tg, tergite. Scale bar, 0.1 mm.

FIGURES 15 – 20. Arthropeina fulva. 15. Genital fork, ventral view. 16. Genital fork, lateral view. 17. Genital fork, dorsal view. 18. Spermatheca. 19. Sternite 8, dorsal view. 20. Female genitalia, dorsal view. Abbreviations: cerc, cercus; go, genital opening; ml, membranous lobe; pp, posterolateral process; ppm, projection of posterior margin; st, sternite; tg, tergite. Scale bar, 0.1 mm.

FIGURES 56 – 59. Female reproductive tracts, including spermathecae of Arthropeina spp. 56. Arthropeina fulva. 57. A. lindneri, sp. nov., paratype. 58. A. melanochroma, sp. nov., paratype. 59. A. pseudofulva, sp. nov., holotype. Scale bar, 0.1 mm.

FIGURES 21 – 26. Arthropeina colombiana, sp. nov., holotype. 21. Genital fork, ventral view. 22. Genital fork, lateral view. 23. Genital fork, dorsal view. 24. Spermatheca. 25. Sternite 8, dorsal view. 26. Female genitalia, dorsal view. Abbreviations: cerc, cercus; go, genital opening; ml, membranous lobe; pp, posterolateral process; ppm, projection of posterior margin; st, sternite; tg, tergite. Scale bar, 0.1 mm.