Eurymerodesmidae, 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 : 7-9

Eurymerodesmidae

An assemblage of derived xystodesmoideans, Eurymerodesmidae is the dominant polydesmidan taxon in prairie ecosystems, and they extend into southeastern forests. They range southward from northeastern Nebraska, eastern Illinois, and southeastern North Carolina to northern peninsular Florida, the Gulf Coast, and the Rio Grande ( Fig. 1 , black line) ( Hoffman 1980, 1982, 1999; Shelley 1990a). The taxon has never been encountered south of this river in Coahuila, Nuevo León, or Tamaulipas states, Mexico, and presently terminates at the International Border. It occurs sympatrically with both Euryuridae and all east-Nearctic xystodesmine tribes except Chonaphini ( Hoffman 1978b, 1980, 1999; Shelley 1982a, b, 1990a, 1994).

Eurymerodesmids are reknown for their pilosities. The acropodital hairs so impressed Wood (1864, 1865), that he characterized the structure as “beset with very numerous long hairs” and named the first species hispidipes. Venters are littered with moderately long hairs in both sexes, but the gonopods and segment 7 in males are especially hirsute. Aperture adornments like caudolateral pockets/pouches and lobes/projections from the caudal margins are moderately to densely hirsute, and long hairs extend (dis) continuously along the “inner” acropodital surfaces as far as the “distal curve/bend,” often terminating in a small “tuft” or denser region. “ Outer” acropodital margins generally lack hairs, but there may be an isolated tuft proximal to the curve. Brölemann (1900) aptly characterized these hairs as long and silken, and those comprising the tuft(s) may be so long and dense as to overlie and largely obscure the short “distal zones.” Despite dissecting hundreds of eurymerodesmid gonopods, RMS has never encountered loose or flimsily attached acropodital hairs nor accidentally dislodged any during handling; all were firmly attached to acropodital stems, and only a few were dislodged and loose in vials after a century of preservation. This fact suggests that conditions in which hairs are discontinuous or extend only short distances along stems are natural, do not reflect accidental losses during the millipeds’ lives, and are not artifacts of samplings, dissections, and/or examinations. Contrastingly, acropodites of east-Nearctic xystodesmine tribes ( Apheloriini , Pachydesmini , Rhysodesmini ) typically exhibit short stretches of comparatively short hairs along the “outer” surfaces of the “prefemoral extensions” that run for only 1/3 of the structures’ lengths. These attributes of eurymerodesminans and nannariinans are even evident in published illustrations; for example, Chamberlin (1949, Fig. 1 , reproduced here with permission as Fig. 8-9 , the latter without the “prefemoral process”) shows discontinuous hairs along the “inner” acropodital surface of N. cayugae Chamberlin followed by a gap and a slight apical tuft. We therefore believe that (dis)continuous stretches of moderately long to long hairs on “inne r ” acropodital surfaces coupled with apical tufts constitute shared features between Eurymerodesmidae and Nannariini, an unquestioned component of Xystodesmidae ( Hoffman 1964a, 1980, 1999; Marek 2014; Hennen and Shelley 2015), and since it is related to such, Eurymerodesmidae must also belong to Xystodesmidae and submerged under the older familial name.

Affinity between Eurymerodesmidae and Nannariini is also revealed by a shared acropodital con- figuration that we interpret as plesiomorphic. Shelley (1990a) characterized the basic eurymerodesmid structure as simple and “stick-like,” with stems extending sublinearly from the prefemur and bending/ curving subapically. This configuration also exists in plesiomorphic nannariinines, but it is less noticeable because the “prefemoral process” tends to mask the acropodite. Although not rotated 180°, the acropodite of N. cayugae ( Chamberlin 1949, Fig. 1 ; Fig. 8–9 ) matches that of plesiomorphic eurymerodesmids, and, coupled with the similar hair lengths and arrangements (compare Fig. 8–9 and 12–15 ) has constituted published, but unperceived, evidence of this affinity for 69 years. “Stick-like” acropodites, or ones that conceivably derive from this condition, also occur in representatives of Devilleini , Rhysodesmini , Apheloriini , and Pachydesmini , so we believe that this simple structure constitutes the basic, plesiomorphic configuration that is thickened, expanded, prolonged, shortened, ornamented, curved, coiled, etc., in these and other xystodesmine tribes. We therefore reduce Eurymerodesmidae to tribal status under Euryurinae , the older name, and propose Eurymerodesmini, n. stat., to encompass subtribes Eurymerodesmina and Nannariina Hoffman, n. stats., the latter transferred from Xystodesminae ( Hoffman 1964a, 1980, 1999; Marek et al. 2014). Because of the longer acropodital hairs that extend along the “inner” surface to the level of the “distal curve/bend” in at least plesiomorphic forms, Nannariina are grouped with Eurymerodesmina and reduced to subtribal status.

Affinity between Eurymerodesmina and Nannariina is further supported by their comparably small body sizes and their distributions, which overlap in Illinois, Missouri, and Arkansas ( Fig. 1 , 16 ), the logical source area for Eurymerodesmini. Nannariina expanded eastward while Eurymerodesmina spread southwestward and then southward and eastward after the Western Inland Seaway receded during the late Cretaceous. While divergence could have occurred post-Cretaceous and hence relatively recently, we believe it came prior to the Seaway and Cretaceous because most of Nannariina’s area was land during this geological period enabling the taxon to spread without impediment. Eurymerodesmina would have spread southward then only to be inundated and eradicated from the area of the Seaway, we believe its presence today in the Plains and southern/southeastern states reflects secondary dispersal and reoccupation of a previously inhabited area, and its occurrence in non-inundated southeastern North Carolina reflects northward post-Cretaceous dispersal along the Atlantic Coast. The partial geographic overlap of Eurymerodesmina and Nannariina supports our sister-group hypothesis; they share ances- try, diverged in the present area of overlap, dispersed in opposing directions, and logically comprise a separate tribe, Eurymerodesmini, in Euryurinae . The belated detection of this relationship despite over a half-century of clues in published literature emphasizes the need for comprehensive anatomical knowledge of all relevant taxa by specialists addressing nebulous and confused situations.

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.

Figure 16. Distribution of Eurymerodesmini plotted against the maximal extend of the Cretaceous Western Inland Sea. Black line, Eurymerodesmina. Red line, Nannariina.

Figures 8–15. Eurymerodesmini gonopodal tel-/acropodites; 8–11, Nannariina. 8) telopodite of Nannaria cayugae Chamberlin, Tompkins Co., NY. 9) acropodite of the same. 10) telopodite of Mimuloria castanea (McNeill), Monroe Co., IN. 11) the same of M. d. dilatata Hennen and Shelley, Marshall Co., TN. 12–15, Eurymerodesmina. 12) Eurymerodesmus varius louisianae Chamberlin, Natchitoches Par., LA. 13) acropodite of a second individual from the same locality. 14) the same, Columbia Co., AR. 15) E. v. varius (McNeill), Escambia Co., FL. Figures 8–9 reprinted from Chamberlin (1949) with permission from the Biological Society of Washington. Figures 10–11 reprinted from Hennen and Shelley (2015) with permission of the Center for Systematic Entomology. Figures 12–15 reprinted from Shelley (1990a) with permission of the American Entomological Society.