Nearctodesmidae Chamberlin and Hoffman, 1950

Shelley, Rowland M. & Shear, William A., 2006, Leonardesmus injucundus, n. gen., n. sp., an aromatic, small-bodied milliped from Washington State, U. S. A., and a revised account of the family Nearctodesmidae (Polydesmida), Zootaxa 1176 (1), pp. 1-16 : 2-5

Family Nearctodesmidae Chamberlin and Hoffman, 1950

Nearctodesmidae Chamberlin & Hoffman, 1950: 1–2 . Shelley, 1994: 477–478 (earlier synonymys cited herein); 2002 a:107. Hoffman, 1999: 459.

Diagnosis (adapted from that of Shelley (1994)). Minute to large­bodied Poly­ desmidea characterized by flattened to moderately convex dorsa, tergites either smooth and with shallow transverse grooves or traces of polygonal areas, or with 3–6 rows of low, rounded, setose tubercles. Coloration varying from pallid to light yellowish­brown, pink, dark reddish brown, or maroon. Gonopods with horizontal or ventrally curved prefemora clearly demarcated from, or merging imperceptibly with, structurally variable, subvertical acropodites, with one or two additional, structurally variable secondary projections (processes "A" & "B") arising near prefemoral/acropodal juncture and extending ventrad to varying degrees, acropodite continuing ventrad beyond origin of solenomere into variable "distal zone"; solenomere arising subterminally from acropodite, slender and variably curvilinear, twisted, or coiled, apically subacuminate. Cyphopods variable, with or without sclerotized extensions arising from common ventral surface and extending dorsad to point of fusion.

Components. Seven genera are definitely referrable to the Nearctodesmidae ; the three southwestern genera of "micro­nearctodesmids," indicated below by question marks, are placed here tentatively pending results of the investigations by RMS: Nearctodesmus Silvestri, 1910 ; Kepolydesmus Chamberlin, 1910 ; Sakophallus Chamberlin, 1942 (= Jaliscodesmus Hoffman, 1975 ); Ergodesmus Chamberlin, 1949 (= Ectopodesmus Hoffman, 1962 ); Harpogonopus Loomis, 1960 ; Bistolodesmus Shelley, 1994 ; Leonardesmus , new genus;? Tidesmus Chamberlin, 1943 ;? Oodedesmus Loomis, 1960 ;? Phreatodesmus Loomis, 1960 . Harpogonopus , Oodedesmus , and Phreatodesmus 1 were assigned to the Fuhrmannodesmidae by Golovatch (1994) and Hoffman (1999); Hoffman (1980) placed these taxa and Tidesmus in the superfamily Trichopolydesmoidea , but was uncertain as to their familial position.

Distribution. Western, southcentral, and southern/southeastern British Columbia (BC), Canada; southern and western Illinois (caves only) and the western US; and western and northwestern Mexico ( Fig. 2 ) ( Chamberlin & Hoffman 1950, 1958; Hoffman 1962, 1975, 1980, 1999; Shear 1969; Shelley 1990, 1994, 2002 a, b; Whitney & Shelley 1995). The distribution extends the length of coastal British Columbia and its offshore islands, including Vancouver Island, as far north as Prince Rupert and the Queen Charlotte Islands, and ranges inland to the Cascade Range east of Vancouver. There are also two disjunct areas, the Shuswap Region around Salmon Arm & Sicamous in southcentral BC, where an allopatric population of Nearctodesmus insulanus (Chamberlin, 1941) occurs, and the southern/southeastern fringe around Creston & Yahk, along the International Border and continuous with the region in the adjacent US (northern Idaho and environs) ( Kevan 1983;

1. We do not consider the enigmatic species, P. hastingsus (Chamberlin, 1941) , from Monterey Co., California, to be a true component of this genus. Originally described in the European genus Brachydesmus Heller, 1858 , hastingsus was transferred to Phreatodesmus by Loomis (1960) and retained there by subsequent authors ( Buckett 1964; Shelley 1997, 2002 a; Hoffman 1999) for lack of a better alternative. Shelley (1997) discussed the difficulties involving this species, whose identity and true generic placement cannot be determined until a topotypical male is collected.

Shelley 1990, 1994, 2002 b; Whitney & Shelley 1995). Nearctodesmids are unknown from Alaska, which has never been systematically sampled for diplopods, but we believe that N. insulanus surely occurs in the southern "panhandle" near Prince Rupert, for example the southern part of Misty Fiords National Monument, southern Prince of Wales Island, and around Ketchikan and Metlkatla on Revillagigedo and Annette islands, respectively.

In the US, the Nearctodesmidae occupies two narrowly detached regions in the PNW that Shelley (1994, fig. 1) showed as joining along the Washington / Oregon border. The western one lies along the Pacific Coast from the border with southwestern BC to San Francisco Bay and extends eastward essentially to the Columbia River in central Washington and the crest of the Cascade Mountains in northern Oregon. The region narrows to the south as its eastern border angles progressively southwestward, and it comprises just a narrow strip in the Coast Range and along the ocean in Mendocino, Sonoma, and Marin cos., California. The eastern region is centered in the northern Rocky Mountains of Idaho (primarily north of the Salmon River), eastern Washington, and western Montana. It crosses the International Border into the adjacent southern fringe of BC (see above), ranges eastward to just across the Continental Divide in Lewis & Clark Co., Montana (Loomis & Schmitt 1970, Shelley 1994), and extends southward along the Snake River to the southern extremity of Hells Canyon in Baker Co., Oregon. A second species of Ergodesmus , the easternmost PNW genus, inhabits caves in five counties of western and southern Illinois that border the Mississippi and Ohio Rivers ( Hoffman 1962, 1999; Shear 1969). It lacks traditional cave­related anatomical modifications, so Shelley (1994) labeled it a "subterranean obligate" whose apparent restriction to caves results from survival in them as "refugia," probably during glaciation.

Farther south in the western US, Harpogonopus occurs in west­facing canyons that drain to the Pacific from the vicinity of Santa Barbara to near Colonet, Baja California Norté (BCN), some 75 mi (120 km) south of Ensenada and 150 mi (240 km) south of the International Border ( Shelley 1993). Records exist from every county in this part of California, some being around 45 mi (72 km) inland in San Diego Co., on Mt. Palomar and in the Laguna Mountains in the Cleveland National Forest. One species each of Phreatodesmus and Tidesmus occurs within the area of Harpogonopus , from near Los Angeles to Ensenada, but otherwise, these genera and Oodedesmus are known from sporadic collections around desert springs or in inselberg mountains as far east as the Dripping Springs Mountains and Superstition Wilderness, Tonto National Forest, Arizona, approximately 365 mi (584 km) from the Pacific. Records are available from Kern, San Bernardino, and Riverside cos., California; Pima, Pinal/Gila, and Maricopa cos., Arizona; and Lincoln Co., Nevada ( Chamberlin 1943, Loomis 1960, Buckett 1964, Hoffman 1999, Shelley 2002 a), and unpublished samples in the NCSM, NMNH, and VMNH are available from Tulare Co., California, and Mojave and Pima cos., Arizona. Hoffman (1999) reported Oodedesmus from Yavapai Co., Arizona, based on another unpublished sample at the VMNH.

Only two Mexican nearctodesmid records are available aside from those of Har­ pogonopus and Phreatodesmus in BCN, these being the localities of Sakophallus in Michoacan and Jalisco. However, comparable occurrence should be anticipated in the desert regions of Sonora, Sinaloa, BCN, and possibly Baja California Sur as in Arizona, Nevada, and California. The record of Oodedesmus from the Baboquivari Mountains, Pima Co., Arizona ( Loomis 1960), for example, is only around 35 mi (56 km) north of the International Border with Mexico, suggesting occurrence in northwestern Sonora.

Remarks. The Nearctodesmidae was established by Chamberlin & Hoffman (1950), who subsequently ( Chamberlin & Hoffman 1958) detailed all species then referrable. While noting that some southwestern genera may also belong, Hoffman (1980) observed that the nearctodesmid gonopod pattern is similar to that of the Macrosternodesmidae Brolemann, 1916 , which he elevated from tribal status under Trichopolydesmidae . Two years later, Hoffman (1982) included Nearctodesmidae with Macrosternodesmidae , the older name, and Simonsen (1990) formally reduced the former to sub­family status. When he revised the Nearctodesmidae, Shelley (1994) was not aware of these works, and Hoffman (1999) reversed his prior conclusion by also recognizing it at the familial level pending study of the "micro­nearctodesmids." Most recently, Shelley (2003 b) also recognized it as a family and noted that Simonsen's action was based on a far too superficial consideration of included forms, so Nearctodesmidae has gone from family to subfamily and back to family again. In transferring Harpogonopus , with two accessory processes, into the taxon, Shelley (1994) noted that it has the basic features of the family, but in such a different arrangement and configuration as to possibly require a separate subfamily; additionally, Ergodesmus and Sakophallus have only one accessory projection (process "B," as "A" is lost) as apparently do the diagnosed "micro­nearctodesmids" in southwestern American deserts (based on the unclear published illustrations of Chamberlin (1943) and Loomis (1960)). This diversity indicates a sizeable, complex taxon with potentially three or more subfamilies, and the discovery of Leonardesmus in the PNW adds still more diversity. While the proposal of a taxonomy cannot proceed until the "micro" forms are studied, the family may potentially involve subfamilies based primarily on the number of accessory branches, with Harpogonopus constituting a separate tribe from the PNW genera with two such projections— Nearctodesmus , Kepolydesmus , and Bistolodesmus . This is entirely speculative, but it emphasizes the intricacy of what is clearly a dominant component of the western US and Mexican diplopod fauna. We therefore reiterate that future students should be alert to the basic nearctodesmid gonopodal pattern of accessory branches and a subterminal solenomere, as more small­bodied polydesmidans are discovered in the adjoining deserts of these two countries.

Figures

FIGURES 2–3. 2, Distribution of the Nearctodesmidae. The dot in southcentral British Columbia represents the allopatric population of Nearctodesmus insulanus in the Shuswap Region; those in California, Nevada, and Arizona, some covering two closely proximate sites, represent known or published localities for the southwestern "micro­nearctodesmids." 3, Known occurrences of Leonardesmus and L. injucundus.