Macrosternodesmidae Brölemann 1916

Shear, William A. & Shelley, Rowland M., 2008, Cave millipeds of the United States. VI. Sequoiadesmus krejcae, n. gen., n. sp., from Sequoia and Kings Canyon National Parks, California, USA (Diplopoda, Polydesmida, Polydesmidea, Macrosternodesmidae)., Zootaxa 1693, pp. 41-48 : 42-43

Family Macrosternodesmidae Brölemann 1916

Diagnosis (adapted from that of Shear and Shelley 2007). Trichopolydesmoidea 6–12 mm long but occasionally growing to ca. 30 mm long, with 20 segments including epiproct; collum narrower than head, not overlapping epicranium; metaterga with transverse sulci and three or four rows of variably rounded to subconical pustules giving rise to clavate setae; paranota small but distinct; male prefemora swollen and convex dorsally; sphaerotrichomes present on at least ambulatory tibiae and tarsi. Gonopodal aperture large, completely filling metazonite, not extending onto prozonite but sometimes spreading caudad between 9th legs. Gonocoxae large, completely filling respective halves of aperture, excavated mediad to accommodate telopodites; prefemora horizontal or angling ventromediad, giving rise to acropodite and additional projection homologous to process B of Nearctodesmidae (terminology of Shelley (1994)); distal zone variably configured, sometimes folded, flattened, and not recognizable as such; solenomere long and narrow, arising subterminally, without hairpad and ampulla, prostatic groove opening terminally.

Remarks. Because of the anatomical similarities between Macrosternodesmidae and Nearctodesmidae and the tendency to assign small-bodied forms to the Polydesmidae , it is appropriate to briefly compare and contrast these taxa. This is a purely heuristic enterprise to benefit North American workers who face the practical problem of diagnosing these three families. While the nearctodesmids and macrosternodesmids are presently placed in the superfamily Trichopolydesmoidea and the polydesmids in the Polydesmoidea, the difficulties inherent in separating them are formidable. This serves only to point to the necessity for a complete reexamination of family-level classification in the Infraorder Polydesmoides. Perhaps the greatest problem in such a project will be the vast numbers of described and undescribed genera from the tropics that are now routinely placed in the “wastebasket” taxon Fuhrmannodesmidae .

In nearctodesmids, the gonocoxae are large and globular, closely appressed or fused caudally but narrowly separated anteriorly, and with limited, if any, mobility. The setose basal part of the telopodite (often, and probably correctly, referenced as the prefemur) is short, compact, and either angles ventromediad or is oriented transversely. Two elongated processes arise at or near the base of the acropodite (sensu Shelley 1994 and Shear & Shelley 2007) and are designated A and B, the former being mesial to the latter. Both may bear teeth and/or subbranches, and A may be absent; we cannot determine whether this is a primitive condition or if the process has been lost. The prostatic groove originates in the prefemur, follows a curvilinear course along the acropodal surface, and terminates apically on the solenomere branch. Distal to this branch is the apical part of the acropodite, termed the distal zone.

The gonopods of North American macrosternodesmids are similar to those of nearctodesmids. All known North American macrosternodesmids lack process A, but possess process B, which is generally longer and broader than in nearctodesmids. Its form and that of the acropodite differ significantly among species presently assigned to Chaetaspis (see Lewis 2002), which is probably why Hoffman (1999) contended that more than one genus is covered by this name. Numerous undescribed macrosternodesmids inhabit the Appalachian Mountains and Mississippi Valley; without detailed knowledge of them, Hoffman’s suggestion, while plausible, cannot be evaluated. In some males of Chaetaspis , the 7th segment is markedly longer (perhaps twice so) than those to the anterior and posterior, and while a slight enlargement is evident in polydesmids, it is never as striking as that in macrosternodesmids.

In polydesmids, the prefemora lie parallel to each other along the body axis; the distal part of the telopodite is not bent, usually constitutes the anterior extremity of the gonopod, and often lies in a prozonal depression that may extend onto the 6th metazonite. Sternal lobes, which are absent from macrosternodesmids, may be present on segments 3–6 of male polydesmids. The prostatic groove, which is actually an internal canal, opens into a small chamber with an outlet pore flush on the acropodal surface that is usually surrounded by fine setae or finger-like cuticular projections, and often subtended by an acute, sometimes branched process.