Xystodesmidae, Cook, 1895

Shelley, Rowland M. & Smith, Jamie M., 2018, Expanded concept and revised taxonomy of the milliped family Xystodesmidae Cook, 1895 (Polydesmida: Leptodesmidea: Xystodesmoidea): incorporations of Euryuridae Pocock, 1909 and Eurymerodesmidae Causey, 1951, taxon revivals / proposals / transferrals, and a distributional update, Insecta Mundi 660, pp. 1-41 : 10-11

Family Xystodesmidae (Adapted from Hoffman (1962a, 1982) and Golovatch and Enghoff (2015))

Diagnosis. Small- to large-bodied (~ 8–85 mm long), moderately convex, usually glabrous, glossy, and smooth-bodied Xystodesmoidea with 20 segments, dorsums usually smoothly glossy black, occasionally pustulate, often adorned with vivid pigmentations (yellow, orange, red, blue, white, lavender, gray) on caudolateral paranotal corners, as bands along anterior margins of collums and caudal metatergal margins, or as spots in metatergal midlines; bodies usually relatively broad (W/L ratio>18%) and subparallel-sided from segments 3–16, occasionally long and slender (W/L ratio <18%); paranota broad, usually declined, occasionally subhorizontal, usually in contact or overlapping when segments compressed, peritremata extending along lateral margins and containing ozopores; antennae moderately long, usually with four but occasionally up to 20 terminal sensory cones, margins of seventh antennomeres not invaginated, cones not grouped into diads; collum usually small, semilunar, and exposing epicranium in dorsal view; epiproct flattened dorsoventrally, usually bluntly subtriangular, broad and spatulate in Euryurina ( Euryurinae : Euryurini ); vasa deferentia opening apically on cylindrical processes on 2 nd legs; ambulatory prefemora with or without sharply acuminate, distoventral spines. Gonopodal aperture primarily on 7 th metazonite and usually relatively large, occasionally extending beyond stricture into prozonite and reducing latter to narrow strip, usually smoothly rounded to ovoid, variably expanded, lobed, or with caudolateral corners flared and anterior margin slightly indented in Eurymerodesmina ( Euryurinae : Eurymerodesmini). Gonopodal coxae joined by either sclerotized sternum, remnant of latter, or membrane, solenite socket completely separated from distal margin. Telopodites in situ usually overlapping, interlocked, or subparallel, extending anteriad and overhanging anterior margin of aperture, subparallel, projecting caudad, and overhanging caudal margin in Eurymerodesmina; comprised of a globular, pilose “prefemur” giving rise to “acropodite” and often one or occasionally two additional and highly variable projections, “prefemur” extending distad for varying lengths along “outer acropodital surfaces,” completely encircling latter in Euryurini and absent from Eurymerodesmina; prefemoral hairs sometimes shorter and extending (dis)continuously along “prefemoral extensions.” “Acropodite” structurally variable, plesiomorphic condition long, slender, and “stick-like,” sublinear or curving/bending distal to midlength, a single projection or divided at varying positions into “solenomere” and one or two variably long additional branches, apomorphically prolonged, shortened, expanded, thickened, twisted, looped, ornamented, cingulate, or varying combinations of these; with at most only a few scattered hairs distal to “prefemoral extension s ” except in Euryurinae where they extend (dis)continuously for varying distances along “inner” or, occasionally, “inner” and “outer” margins beyond “prefemora” or “prefemoral extensions,” hairs varying in lengths and densities, often denser and “tufted” distad.

Components. Three subfamilies, one monobasic and two divided into two or nine tribes.

Distribution ( Fig. 17–21 ). Five major Holarctic regions, one extending into the northernmost continental Neotropics. Xystodesmidae is the dominant and virtually only Holarctic leptodesmidean family, and it is particularly so in the three regions of the New World detailed in the Distribution section. In the Palearctic, it occurs in three areas/subregions of far eastern continental and insular Asia as well as three along the Mediterranean and adjoining seas and in two large and several small islands in southern Europe, northern Africa, and the Middle East. The family is absent from the vast intervening area of Central Asia and overall is known from 22 countries and projected for two others as follows: North and Central America, five countries – Canada, United States, Mexico, Guatemala, El Salvador (projected for Belize and Honduras); Africa, two countries – Morocco, Algeria; Europe, six countries – France, Italy (“mainland” and Sardinia), Albania, Macedonia, Greece, Turkey; Mediterranean Islands, one country—Cyprus; Asia Middle East, one country—Turkey, Asia Far East, seven countries—Russia, North Korea, South Korea, Japan, Taiwan, China, Vietnam.

Remarks. With the incorporation of Euryuridae and Eurymerodesmidae , Xystodesmidae essentially becomes a “catch-all” taxon and the Holarctic leptodesmidean counterpart to the primarily Neo- and Afrotropical Chelodesmidae (Chelodesmoidea) . The ventrodistal spine on the ambulatory prefemora that has been considered diagnostic only occurs in four east-Nearctic taxa: Nannariina ( Euryurinae ) and Apheloriini , Pachydesmini , and Rhysodesmini (Xystodesminae) . Practically every character has an exception, particularly in Euryurinae . The primary unifying feature is its Holarctic distribution, but even this has an exception, the northern continental Neotropics. These additions overwhelmingly render Xystodesmidae the dominant leptodesmidean taxon in the Northern Hemisphere or land masses deriving from the supercontinent Laurasia. Only three other leptodesmidean families inhabit continental regions of this enormous area: Sphaeriodesmidae (Sphaeriodesmoidea) , a Neotropical immigrant represented by the two species of Desmonus Cook in the southern/southeastern US ( Cook 1898; Causey 1958; Chamberlin and Hoffman 1958; Hoffman 1980, 1999; Shelley 2000a); Chelodesmidae (Chelodesmoidea) , represented by Cantabrodesmus lorioli Mauriès , in caves in northern Spain ( Mauriès 1971, 1974; Luque and Labrada 2017) and, with our action, Macellolophus excavatus Verhoeff , in southeastern Spain ( Verhoeff 1931; Attems 1940; Mauriès 1978; Mauriès and Vicente 1978; Vicente 1988; Ceuca 1988; Mauriès et al. 2006); and Oxydesmidae (Xystodesmoidea) , represented by the two species of Libanaphe Hoffman in the coastal Middle East ( Lebanon and Israel) ( Hoffman 1963; Tabacaru 1995; Golovatch 2007).

Figures

Figure 17. Global distribution of Xystodesmidae.

Figure 18. The East-Nearctic Region of Xystodesmidae. The eastern- and northernmost dots denote localities of the two Appalachian species of Rhysodesmus; the dot in Texas within the black line signifies the northernmost locality of R. texicolens (Chamberlin), San Diego, Duval Co. The arrow indicates Bald Head Island, NC, occupied by Apheloria (Xystodesminae: Apheloriini).

Figure 19. The West-Nearctic Region of Xystodesmidae. Left, Pacific Coastal Subregion. Right, Western Interior Subregion. The detached, cluster of dots to the south show the area of Motyxia monica Chamberlin in the Santa Monica Mountains and northern metropolitan Los Angeles.

Figure 20. The East-Palearctic/East-Asian Region of Xystodesmidae. The arrow points to the site at Cuc Phuong National Park, Vietnam.

Figure 21. Distribution of the polydesmidan suborder Leptodesmidea in the Mediterranean Region of Europe, Africa, and Middle Eastern Asia. Black lines and dots, West-Palearctic Region of Xystodesmidae. Red line, area of Spain/Iberian Peninsula occupied by Macellolophus excavatus (Chelodesmidae). Red stars, localities in the same of Cantabrodesmus lorioli (Chelodesmidae). Green triangles, denoted by green arrow in eastern Mediterranean Sea, localities of Libanaphe spp. (Oxydesmidae) in Lebanon and Israel.