Eurymerodesmina Causey 1951

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 : 13-14

Subtribe Eurymerodesmina Causey 1951 , New Status

Diagnosis. Stiff and inflexible Eurymerodesmini, mandibular stipes with basal ridges extending into variable projections, postgonopodal sterna of males and all sterna of females hairy and without spines, caudal margins sublinear or gently curved, ambulatory prefemora without ventral spines, pregonopodal tarsal claws in males acuminate, gently curved or bisinuate. Gonopodal aperture usually heavily pilose, often enlarged or ornamented with variable configurations, anterior margin usually slightly indented, lateral margins simple or divided near midlengths into flared inner and outer margins forming hirsute pouches at caudolateral corners, caudal margins with or without densely hirsute subtriangular or clavate lobes, latter usually extending below level of adjacent ambulatory coxae. Gonopods laterally oriented, each rotated 180° in situ with cannulae laterad and telopodites extending caudad and overhanging caudal aperture margins; telopodites without prefemoral processes and extensions; acropodites arising directly from prefemora, hairs long and thickened, extending (dis)continuously varying distances along stems to “distal bends” or ~7/8ths of acropodital lengths, usually with variably dense tufts apically on “inner” or “inner” and “outer” margins, former overhanging and partly obscuring bends and much of “distal zones”; cyphopodal valves large and hirsute, distal corners often modified into ridges and variable projections, occasionally long, dactyliform, and protruding through cyphopodal aperture.

Component. Eurymerodesmus Brölemann (syns. Kewanius and Paresmus , both by Chamberlin) ( Shelley 1990a, Hoffman 1999).

Distribution ( Fig. 1 , black line, 16). East-Nearctic, endemic to the central, southcentral, and southeastern US. Eurymerodesmina occur, north/south, from northeastern Nebraska, the Missouri River in Missouri, central Illinois, the Fall Zone region of the southeast, and the Atlantic Coast of southeastern North Carolina to northern peninsular Florida and the Gulf Coasts of the Panhandle through Texas to the Rio Grande. East/west, they extends from the Atlantic Coasts of southeastern North Carolina through northeastern Florida to eastern Nebraska, the plains of central Kansas and southwestern Oklahoma, the Edwards Plateau of central Texas, and west of the Pecos River near its confluence with the Rio Grande.

Remarks. While Shelley (1990a) addressed virtually every aspect of Eurymerodesmus , a few bear repeating here. In addition to each gonopod’s being rotated 180° in the aperture such that the cannula is lateral instead of medial and the acropodites extend caudad in situ overhanging the caudal, rather than the anterior, aperture margins, the genus and its higher taxa reverse the overall gonopodal condition in both Xystodesmoidea and Leptodesmidea. To our knowledge, the apertures are simple and unmodified while the gonopods are elaborate and ornate in most representatives of these taxa. Likewise, while the lengths of the acropodital hairs vary, the long ones that usually extend well down the stems are the most conspicuous and contrast markedly with the short hairs in xystodesmines that are primarily basal and restricted to the “prefemoral extensions.” The hairs actually comprise two or three rows, and the apical tufts have from 4–18 hairs that substantially overhang the “distal zones”, with the higher numbers of hairs obscuring the latter.

Previously, the cumulative weight of the host of autapomorphies left no alternative to according separate familial status to Eurymerodesmus , and even now, its ties to the rest of Xystodesmidae seem weak compared to the magnitude of unique features. However, anatomical connections undeniably exist through Nannariini, and as Eurymerodesmus shares ancestry with an unquestioned xystodesmid component, it must also belong to the family. Like Chelodesmidae in the Neo- and Afrotropics, Xystodesmidae is thus a “catch-all,” heterogeneous assemblage with no single unifying anatomical feature. The ventrodistal spines on the ambulatory prefemora are shared only by Nannariina and the endemic east-Nearctic xystodesmine tribes—Apheloriini, Pachydesmini , and Rhysodesmini—as now constituted. No west-Nearctic tribe possesses the spine including Chonaphini , represented in the east by only Semionellus Chamberlin. Additionally , while Eurymerodesmus spp. tend to be smaller than sympatric xystodesmines, the convex dorsums and general facies are so similar that adults can be mistaken for juveniles of the latter, and juveniles of these taxa are virtually indistinguishable. Consequently, we submerge Eurymerodesmidae under Euryurinae , which holds 42 years of priority for the family-group name, the shared “hairiness” alone constitutes evidence of common ancestry and a sufficiently close relationship to justify this action.

Figures

Figure 1. Distribution of Euryurinae plotted against the maximal extent of the Cretaceous Western Inland Sea. Euryurina (Euryurini, red), Eurymerodesmina (Eurymerodesmini, black), Nannariina (Eurymerodesmini, green). The red line, Euryurina, in eastern North Carolina and southcentral Virginia connects disparate peripheral localities; the area of greatest euryurinan concentration is circumscribed by the red dots.