Chicobolus Chamberlin, 1947

Shelley, Rowland M. & Floyd, Samuel D., 2014, Expanded concept of the milliped family Spirobolidae Diplopoda: Spirobolida: Spirobolidea): Proposals of Aztecolini n. tribe and Floridobolinae / ini and Tylobolini n. stats.; (re) descriptions of Floridobolus and F. penneri, both Causey, 1957, and F. orini n. sp.; hypotheses on origins and affinities, Insecta Mundi 2014 (357), pp. 1-50 : 27-28

Genus Chicobolus Chamberlin, 1947

Chicobolus Chamberlin, 1947:46 . Causey, 1955a:75–76. Chamberlin and Hoffman, 1958:162. Hoffman and Keeton, 1960:11. Keeton, 1960a:39–40. Jeekel, 1971:195. Hoffman, 1980a:76; 1999:37. Shelley, 2001a:244 .

Incobolus Chamberlin, 1955:7 . Hoffman and Keeton, 1960:15. Jeekel, 1971:199.

Type-species. Of Chicobolus , C. pilsbryi Chamberlin, 1947 , by original designation; of Incobolus , I. thaumastus Chamberlin, 1955 , by original designation.

Diagnosis. Posterior gonopod telopodite leaning mediad. Prefemoral process relatively short, at most extending only to level of acropodital midlength. Anterior acropodital margin deeply incised distal to midlength, with adjacent spiniform projection.

Component. Keeton’s (1960a) concept, that Chicobolus is monotypic, has been accepted by all subsequent authors (Hoffman 1980, 1999; Shelley 2001a ). We continue this pattern, although the strikingly different color pattern of populations in the Keys and southernmost peninsula suggests that they should be re-examined for structural differences justifying specific recognition (the name, C. pilbryi Chamberlin, 1947 , is available), as should the South Carolina population.

Distribution ( Fig. 28 , letter C). Chicobolus and C. spinigerus are essentially restricted to the area in the four southeasternmost states that were completely inundated during the Cretaceous, and as noted in the tribal account, the taxa may already be gone from Alabama and western Florida. The northernmost locality is in Florence Co., South Carolina; the southernmost is on Big Pine Key, Monroe Co., Florida, where a thriving population apparently exists; and the westernmost is Pensacola, Escambia Co. Maximal dimensions are 1,110 km (694 mi), north-south, and 701 km (438 mi), east-west, but those for the continuous area with maximal abundance ( Fig. 28 , black line) are 760 km (475 mi), north-south, and 467 km (292 mi), east-west. We think the main population and that in coastal South Carolina, around 296 km (185 mi) to the north, will eventually be the only ones, with the latter subsequently disappearing leaving only the primary one, which will shrink to peninsular Florida and the Keys as Narceus ousts Chicobolus from Georgia and northern Florida. The area may continue shrinking, as Narceus spreads through the southernmost peninsula, and Chicobolus may eventually be restricted to the Keys, which are protected by marine barriers that the former cannot breach. However, rising sea levels coupled with the abundances of the introduced families Rhinocricidae and Trigoniulidae , which are overrunning the Keys and southernmost peninsula ( Shelley and Edwards 2002, Shelley et al. 2005), may eliminate Chicobolus from these refugia.

Origin. We do not know exactly when in the Cretaceous the generically distinct US aztecolinine actually arose. It could have been anytime during aztecolinine dispersion, but separate generic status was finalized when the Western Interior Seaway severed the last strand of genetic continuity. We therefore arbitrarily select <104 mya, the mid-Cretaceous when we place all dispersions in Appalachia, as the origination date of Chicobolus .

Remarks. Again, Keeton (1960a) was remarkably prescient in regarding Chicobolus as deriving from an Aztecolus -like ancestor that lacked distal modifications of the posterior gonopod telopodite, which is essentially also our conclusion.

Figures

Figure 28. Distribution of Aztecolini plotted against Cretaceous land patterns; submerged, marine Florida terrane and approximate maximal dimensions of the Western Interior Seaway in light blue. Ap, Appalachia. AZ, Aztecolus. C, Chicobolus. L, Laramidia. SA, Presumptive Source Area in the “northern Mexican Highlands.” The area encircled with brown squares is that of Tylobolini/Hiltonius/H. carpinus; the area where Aztecolus and Tylobolini/Hiltonius overlap is plausibly the source area.