Figures. 10D, 13A, 15J–L, 17I, 18B, 20
Type material. HOLOTYPE, male, in NZAC, labeled: \ Ridge above Onekaka. Iron ore pit \ 20.v. 67 F. Alack \ litter 67/205 \ DSIR \ No \. PARATYPES (5 specimens, dissected 3), 1 male labeled: \ litter Nelson, N. Z. Parapara Inlet G.B. 15.II.72 J.I. Townsend \ J.I. Townsend Collection \; 1 female labeled: \ PuPu Valley 21.v. 67 F. Alack \ litter 67/204 \ DSIR \ No \ NZ PB \; 1 female labeled: \ PuPu Valley Takaka, Nelson 11 Nov. 71 J.I. Townsend \ NZ PB \; 1 female labeled: \ Paramahoi Nel. Litter 26-10- 65 L. P. Marchaut \ NZ PB \; 1 female labeled: \ Paramahoi Takaka Dist. Nel. 25.10.65 \ J.I. Townsend \.
Etymology. The specific epithet is a Latin adjective (from Latin rotundus meaning “round, circular” and collum meaning “neck”) in the masculine form and refers to the shape of pronotum of the new species.
Type locality. New Zealand, South Island, Nelson, Kahurangi National Park, Onekaka area.
Recognition. Adults of this species (Fig. 10D) are practically indistinguishable from the adults of many Nesamblyops species based on external characters (e.g., Figs 10E–F, 11A–B) and are distinguished from them by the structures of the male genitalia.
Description. Large for genus (SBL range 1.84–2.07 mm, mean 1.92± 0.103 mm, n=4).
Habitus. Body form (Fig. 10D) moderately convex, elongate ovoid, general proportions slightly wide (WE/SBL 0.39±0.009), head narrow relative to pronotum (WH/WPm 0.70±0.014), proportions of pronotum in comparison to elytra average for genus (WPm/WE 0.72±0.006).
Color. Body color brunneorufous, appendages testaceous.
Prothorax. Pronotum (Fig. 13A) moderately long in comparison to elytra (LP/LE 0.41±0.006) and slightly transverse (WPm/LP 1.16±0.019), with lateral margins slightly and rectilinear constricted posteriorly (WPm/ WPp 1.22±0.023). Anterior angles indistinct, posterior angles obtuse (115–124°), widely rounded. Width between posterior angles greater than between anterior angles (WPa/WPp 0.85±0.041). Basal margin slightly convex.
Elytra. Ovoid, moderately depressed along suture, comparatively long (LE/SBL 0.59±0.002) and moderately wide (WE/LE 0.66±0.015). Humeri completely rounded. Lateral margins slightly divergent at basal third, subparallel at middle and evenly rounded to apex in apical third.
Male genitalia. Median lobe of aedeagus (Fig. 15L) moderately arcuate and slightly twisted. Shaft almost subparallel in basal half, moderately tapering in apical half. Apex straight, subparallel and long with asymmetrically rounded wide tip. Apical orifice long, occupies almost half of the shaft length. Ventral margin of median lobe almost straight. Walls of shaft with group of poriferous canals at basal orifice. Dorsal copulatory sclerites atypical for genus. V-contour and rC-sclerite lacking. Instead of them only one dorsal membraneous field exists at the middle of shaft (Fig. 15L). The field has narrow sclerotization along its dorsal edge presumably corresponding to the dorsal branch of V-contour. Additionally, internal sac has scaly membraneous field of moderate size at apical orifice. Left paramere (Fig. 15J) comparatively narrow, with attenuate apex, bearing two long setae. Right paramere (Fig. 15K) narrow, of moderate length, bearing two long setae, which are shorter than the length of paramere. Ring sclerite as in Fig. 17I.
Female internal genitalia. Spermatheca (Fig. 18B) with two sclerotized compartments, a larger ball-shaped distal part and a short, curved, tube-like part representing sclerotized continuation of spermathecal duct. Tube-like part bears spermathecal gland, which is longer than the length of spermatheca. Spermathecal duct short, approximately equals the length of spermathecal gland.
Geographical distribution. The range of the species lies in the northwest corner of the South Island at the northeastern part of the Kahurangi National Park, where the species was collected on the eastern slopes of Parapara Peak (Fig. 20, pink circles).
Habitat. Specimens were collected mostly from litter samples.
Relationships. The structures of the male genitalia and parameres of N. rotundicollis suggests its relatedness to N. solitarius and N. subrufus, described below. All three species share bisetose parameres, the lack of rC-sclerite, and a scaly membraneous field near apical orifice in the internal sac of median lobe, the latter is presumably a synapomorphic character of this small group of species.