Retrorsia simplicissima Shear & Marek, 2021

Shear, William A. & Marek, Paul E., 2021, Three new genera and eighteen new species of miniature polydesmid millipedes from the northwestern United States (Diplopoda, Polydesmida, Polydesmidae), Zootaxa 4975 (1), pp. 81-126 : 101-103

Retrorsia simplicissima Shear & Marek , n. sp.

Figs 50–52 , 126

Type. Male holotype from Stillman Basin , 1.8 miles on Weyerhauser Road 4200 from Road 4000, 2116 ft asl, 46.4956°, -123.2134°, Lewis Co., Washington, collected 4 December 2004 by W. Leonard and C. Richart. The holotype is mounted on SEM stub WS 33–11, deposited in CAS .

Diagnosis. The gonopod ( Fig 126 ) is extremely simple, with the pulvillus about midway in its length, and only a hint of a pulvillar notch. The terminal zone tip is undivided and slightly retrorse. The anterior marginal setal row of the collum consists of 22 setae ( Fig. 50 ).

Etymology. The species name, an adjective, refers to the simple gonopods.

Description. Length about 5.0 mm, greatest width 0.46 mm. Anterior metazonites ( Figs 50, 51 ) with four rows of setae, a few posterior segments may appear to have five rows due to intercalated setae. Epiproct not swollen, short. Anterior legs crassate, tarsi with sphaerotrichomes. Gonopod ( Fig. 126 ) with small prefemorite. Acropodite relatively short, stout, pulvillus near midlength of acropodite, pulvillar notch small, shallow, indicated by slight swelling immediately distal. Terminal zone simple, only slightly retrorse. Female unknown.

Distribution. Only known from the type locality.

Notes. This species seems marginal to our concept of Retrorsia , though the general appearance of the gonopod in comparison to the other species suggests it belongs here. The gonopod is among the simplest to be found in the family Polydesmidae .

Figures

FIGURES 50–55. Species of Retrorsia and Retrorsioides, n. gen. 50–52. Retrorsia simplicissima, n. sp. 50. Head and anterior rings, dorsal view. 51. Midbody ring, dorsal view. 52. Pygidium, lateral view. SEM stub WS33-11. 53–55. Retrorsioides castellum, n. sp. 53. Head and anterior rings, dorsal view. 53. Midbody ring, dorsal view. 55. Pygidium, lateral view. SEM stub WS32-17.

FIGURES 121–126. Drawings of gonopods of polydesmid species. 121. Left gonopod of Retrorisia leonardi, mesal view. 122. Left gonopod of Retrorsia benedictae, mesal view. 123. Left gonopod of Retrorsia richarti,n. sp., mesal view. 124. Right gonopod of Retrorsia gracilis, n. sp., lateral view. 125, Gonopod tip of Retrorsia gracilis, mesal view. 126. Right gonopod of Retrorsia simplicissima, n. sp., lateral view.