Psammodesmus Cook, 1895

Hoffman, Richard L., Martinez, Daniela & D, Eduardo Florez, 2011, A new Colombian species in the milliped genus Psammodesmus, symbiotic host for bryophytes (Polydesmida: Platyrhacidae), Zootaxa 3015, pp. 52-60 : 53

Genus Psammodesmus Cook, 1895

Psammodesmus Cook, 1895 , Brandtia 12: 52. Monobasic with a new species. Type species: P. c o s Cook, by original designation. — Silvestri, 1897, Boll. Mus. Torino, 12(305): 15. — Hoffman, 1953, Journ. Washington Acad. Sci. 43: 301.— Hoffman, 1980, Classification of the Diplopoda, p. 163. —Hoffman, 1999, Va. Mus. Nat. Hist. Spec. Publ. 9: 398.

Ernostyx Chamberlin, 1941 , Bull. American Mus,. Nat. Hist., 78: 497. Monobasic with a new species. Type species: E. dasys Chamberlin , by original designation. Synonymized with Psammodesmus by Hoffman, 1953.

Diagnosis. Terminal lamina of gonopod directed either distad or ventromesad (away from the coxa), solenomere in either case directed sinuously ventrad, in contrast to other Neotropical genera in which both of the apical elements are curved or bent dorsad, thus in the same axis as the coxa.

Comments. The identification of this genus has been solely by circumstantial evidence. The type species was based on a female specimen never seen since Cook’s day: not in any likely despository, and presumably lost/misplaced. The original description, which could apply to any number of platyrhacids, is as follows:

“ Carinae of moderate width, with a prominent, square shoulder at base in front; dorsum densely beset with distinct, prominent, rounded granules and divided into three transverse rows of polygonal areas, each of which has a distinct, though not conspicuous tubercle in the middle; tubercles of the posterior row much more conspicuous than the others; first segment with an anterior row of large tubercles, behind which is a distinct transverse depression; vertex densely and finely granular, prominent and cristate on each side of the sulcus; pores removed from the margin by five or six times the diameter of the small ring; clypeus smooth and shining below: Genus Psammodesmus nov., type Ps. cos , sp. n., Colombia, Philadelphia Academy.”

Shortly after publication of this account, F. Silvestri described two new platyrhacids from Ecuador, Psammodesmus camerani (1897) from Gualaquiza and P. fasciolatus (1898) from the Rio Peripa, both collected by the renowned Italian ornithologist Enrico Festa. It is not obvious how Silvestri deduced that these species were congeneric with Cook’s rather ambiguously described type species. His confidence was not shared by the next writer on these millipeds, H. W. Brolemann (1919) who in reporting specimens from western Ecuador that he identified as fasciolatus , referred the species to Platyrrhacus [sic] rather than Psammodesmus . In this disregard of the Cookian genus, Brolemann was followed by Attems (1938) who placed both fasciolatus and camerani in the subgenus Tirodesmus of his comprehensive genus Platyrhacus . Hoffman (1953) on the other hand ventured to recognize Psammodesmus on the basis of a new species from Panama, and in 1960 went so far as to establish the new tribe Psammodesmini for this one genus, also recognized in the 1980 “Classification”.

The discovery that two platyrhacid species quite distinctive in peripheral characters can share a basically identical gonopod structure imposes an important caveat on future use of illustrations of these appendages in definition or identification of species of platyrhacids. Attention to peripheral characters is now mandated, but even a meticulous description like that of Brolemann (1919) for P. fasciolatus cannot anticipate every detail that future knowledge may require. A precedent to this situation is established in some Nearctic genera of the xystodesmid tribe Rhysodesmini , and the oxydesmid genus Coromus in particular provides a comparable example.