Trigenotyla Causey

Shear, William A., 2003, The milliped family Trichopetalidae, Part 1: Introduction and Genera Trigenotyla Causey, Nannopetalum n. gen., and Causeyella n. gen. (Diplopoda: Chordeumatida, Cleidogonoidea), Zootaxa 321, pp. 1-36 : 18-19

Genus Trigenotyla Causey

Trigenotyla Causey 1951:118 ; 1959:76. Shear, 1972:280. Hoffman, 1999:238 (list).

Type species: Trigenotyla parca Causey 1951 .

Included species: The type, T. vaga Causey 1959 , T. blacki , n. sp., and T. seminole , n. sp.

Diagnosis: Closely related to Causeylla, but differing in the ninth legs of males, in which the coxae extend distal to the articulation with the telopodite. The anterior surfaces of the gonopod coxae lack trichomes. All species with 30 trunk segments; Causey (1951) originally stated that T. parca had 28 segments.

Distribution: Northwestern Arkansas, northeastern and southcentral Oklahoma.

Notes: Trigenotyla species are often, but not always, collected in caves; for many areas, caves are more heavily collected than forest litter habitats, and this may contribute to the preponderance of cave records for this genus. Only T. blacki seems restricted to caves, and only this species shows any troglomorphic adapatations (reduced eyes). It is also very likely that surface populations of Oklahoma Trigenotyla species are active and available for collection in the winter rather than the hot, dry summers that prevail in the region; little collecting is done in winter.

The distribution of Trigenotyla as now understood can be divided into two distinct regions. Trigenotyla parca is known from caves and epigean sites in northwestern Arkansas, while T. blacki has been found in caves across the border in northeastern Oklahoma. The other region is in southcentral Oklahoma, in Seminole , Johnston, Murray, LeFlore, and Latimer Counties.

Latimer County is the type locality of vaga and, with LeFlore County, is a good distance east of the other records. Causey labelled the more western collections as “profunda,” suggesting that she believed them to be a new species. Unfortunately, the type of T. vaga is the only known male specimen, and the gonopods, originally mounted on a slide (AMNH), have been lost (L. Sorkin, pers. comm. 2002). I found that Trigenotyla south of the Canadian River in Murray and Johnston Counties closely conformed to the illustrations of vaga provided by Causey (1959), while there were differences in the specimens from Seminole County north of the Canadian. Therefore, I am naming the Seminole county specimens as a new species, T. seminole , and referring specimens south of the river to T. vaga .

I predict that Trigenotyla species will be found generally in suitable habitats (caves, riverine forests) throughout eastern Oklahoma and western Arkansas when collectors are in the right place at the right time. It also seems likely that the genus will turn up in southwestern Missouri, southeastern Kansas, and northeastern Texas.

Trigenotyla gonopods are similar in general appearance to those of Causeyella species, but in some respects seem more apomorphic. The gonopod setae tend to be ensiform, distinctly so in T. parca , and are divided into two groups, with the typical 3 basal setae. The mesal coxite is broad in two species ( T. seminole and T. vaga ), thin and acute in T. parca , and absent in T. blacki . The ectal coxite in the former two species is very much like that of species of Causeyella and suggests that the latter two are apomorphic in the reduction of the structure. Trichomes are absent from the surfaces of the gonopod coxae, though under high magnification the coxae can be seen to be minutely roughened with tiny, conical projections. It is not clear at present if this is apomorphic (loss of trichomes) or plesiomorphic (partially developed trichomes).

The ninth legs of males are unique among trichopetalids in that the L­shaped coxa is extended distad to the articulation of the telopodite, a modification hinted at in some Causeyella species. Causey (1951) called the basal podomere a coxoprefemur, but if it is homologous to the same podomeres in other trichopetalids, it is the coxa alone, and the large distal joint includes the prefemur and other distal podomeres. In one species ( T. seminole ) there are tiny vestigial podomeres at the end of the prefemur. The form of the prefemur and the presence of these vestigial podomeres suggests that the telopodite article is only the prefemur, and unlike the situation in other genera, does not result from the fusion of other podomeres. The ninth coxa also has an unusually distinct, but likely vestigial, gland.