As has been mentioned in an earlier post, most millipedes tend not to be extravagant in their external variation, and spirobolidan millipedes look about as millipede-y as you can get. Notable features of the spirobolids as a whole include the presence of only a single pair of legs on each of the first five body rings, and modification of the eight and ninth pairs of legs into the gonopods (Milli-PEET). The Rhinocricidae are characterised by a broad collum (the first segment behind the head) with a rounded ventrolateral margin, and the anterior gonopods forming a single, more or less triangular, transverse plate. Sensory pits called scobinae are often present on the dorsal segments (Marek et al. 2003). Below the family level, as with other millipedes, it all comes down to genitalia. In Salpidobolus, the distal section of the posterior gonopods is flagellate and divided into two branches, one branch carrying the seminal channel (Hoffman 1974).
The status of Salpidobolus was most recently reviewed by Hoffman (1974). The majority of species now included in the genus had previously been placed in the separate genera Dinematocricus or Polyconoceras. Salpidobolus was initially restricted to the type species, S. meyeri from Sulawesi, which differs from other species in the presence on the first three pairs of legs of distinct processes on some of the leg segments. Dinematocricus and Polyconoceras were supposed to differ on the basis of the number of sensilla at the end of each antenna: four in Dinematocricus, more than four in Polyconoceras. Hoffman felt that none of these differences warranted generic separation in light of the consistency of gonopod structure between the three 'genera', and united them all under the oldest available name.
Hoffman, R. L. 1974. Studies on spiroboloid millipeds. X. Commentary on the status of Salpidobolus and some related rhinocricid genera. Revue Suisse de Zoologie 81(1): 189–203.
Hudson, B. J., & G. A. Parsons. 1997. Giant millipede ‘burns’ and the eye. Transactions of the Royal Society of Tropical Medicine and Hygiene 91: 183–185.
Marek, P. E., J. E. Bond & P. Sierwald. 2003. Rhinocricidae systematics II: a species catalog of the Rhinocricidae (Diplopoda: Spirobolida) with synonymies. Zootaxa 308: 1–108.