Stenus (Nestus) sphaerops Casey, 1884

Ryvkin, Alexandr B., 2012, New species and records of Stenus (Nestus) of the canaliculatus group, with the erection of a new species group (Insecta: Coleoptera: Staphylinidae: Steninae), European Journal of Taxonomy 13, pp. 1-62 : 40-41

Stenus (Nestus) sphaerops Casey, 1884

( Figs. 6B , 7 I–J)

Stenus sphaerops Casey, 1884: 68 .

Stenus (s. str.) sphaerops – Campbell & Davies 1991: 112.

Material examined

USA: 1 ♂, ‘U.S.A.: New York. S. Westerlo: Bear Swamp. 12VIII:1974. Leg: W. Suter. Albany Co. ’, ‘FM( HD)#74-195. Berlese: Sphagnum . WS#74–61D.’ ( FMNH) .

Differential diagnosis

Based on many external characters, this species might be placed separately within the canaliculatus group. Nevertheless, from the shape and structure of the aedeagus, one can suppose it to be most closely related to the latipennis-illusor-delitor complex. S. sphaerops differs from all the known species of this complex by the broader head with eyes much more convex, by the greater and more bulging pronotum, by the shorter elytra, by the much coarser forebody puncturation, by the less developed ground sculpture, and by the shape of aedeagus.

Redescription

LENGTH. 4.0– 4.1 mm.

COLORATION. The single specimen on hand is somewhat immature; therefore, the genuine coloration is probably darker than described here. Body pitchy black, moderately shining, with fairly short silvery pubescence. Legs dark brown with middle parts of femora somewhat lighter, reddish; antennae reddishbrown with 1 st segment pitchy black and 2 nd segment dark brown; palpi brown, with segment 1 and base of segment 2 yellow.

HEAD. Evidently broader than elytra between humeri (69:62), nearly as broad as elytra in posterior quarter (69:70). Front with a pair of fairly broad and deep longitudinal impressions and a broad keelshaped median elevation that is not very prominent but well developed; median elevation 1.8 times as broad as each of lateral pieces. Puncturation coarse and dense, irregular, partly rugose along internal margins of eyes, with small smooth spot in middle of median longitudinal ridge; diameter of coarsest punctures evidently larger than basal cross of antennal segment 3. Frontal slope before antennal fossae fairly gentle. Antennae long, reaching basal 1/4 of pronotum. Length proportions of antennal segments 2–11 = 8:11.5:10:8:7:7:5:6:6:7.5; segments of club distinctly elongate (6:3.5, 6:4.5, 7.5:4).

PRONOTUM. Distinctively large, bulging, uneven, a bit longer than broad (55:52), broadest near middle of length, narrowed convexly anteriorly and concavely posteriorly. Median longitudinal groove deep over almost entire length of disk, vanishing just behind slightly elevated anterior margin. Laterobasal depressions shallow though laterobasal prominences developed. Puncturation coarse, in part nonrugosely obliquely confluent, distinctly greater in middle of length; punctures much larger than those of head.

ELYTRA. Somewhat broader than long (70:63), nearly as broad between humeri as long (62:63), about 1/7 longer than pronotum (63:55) although a bit shorter than pronotum (53:55) by suture. Humeral angles short but prominent, lateral sides slightly convexly and moderately divergent posteriorly (62:70). Humeral and sutural depressions rather feeble, vanished posteriorly. Puncturation deep, distinctively larger in diameter than that of pronotum, more regular, partly nonrugosely confluent but not forming long furrows.

LEGS. Rather long; segment 1 of metatarsi obviously longer than segment 5 (15:12) though shorter than segments 2–4 together.

ABDOMEN. Moderately convex, with well developed paratergites and two pairs of keels at bases of anterior visible tergites. Lateral sides uniformly convergent posteriorly. Tergite 7 with very fine light fringe at posterior margin. Puncturation of tergites fairly dense, on anterior visible tergites distinctly sparser medioposteriorly; average diameter of punctures on anterior visible tergites about equal to that of median elevation of head.

MICROSCULPTURE. Very fine but regular mesh-like ground sculpture evident between punctures on abdominal tergites 6–10; other surfaces smooth or with infrequent, extremely vague netting mainly by margins of punctures.

MALE. Meso- and metatibiae without specific characters; abdominal sternites 6–7 slightly depressed along midline and slightly emarginated medioposteriorly; abdominal sternite 8 with broad but not deep, rounded emargination of posterior margin and with flat depression in posterior half; lateral pieces uniformly rounded; abdominal sternite 9 as in Fig. 7J ; aedeagus as in Figs. 6B , 7I .

Remarks

Originally described for the male holotype only: ‘Massachusetts’. Campbell & Davies (1991), without citing material, recorded it for the Canadian provinces Ontario, Quebec, and Nova Scotia, as well as the Northwest Territories. The original description, though fairly long and detailed, did not contain some necessary data comparable to those of present-day publications. Inasmuch as neither descriptions nor figures have been provided for S. sphaerops since Casey (1884), I thought it useful to give such a description here.

Figures

Fig. 6. Aedeagus, ventral view. A. Stenus (Nestus) delitor sp. nov. (holotype). B. S. (N.) sphaerops Casey, 1884 (U.S.A.: New York: Albany Co.). – Scales = 0.1 mm.

Fig. 7. ♂ copulative structures. A–I, K: Aedeagus, ventral view. J: Abdominal sternite 9. A. Stenus (Nestus) delitor sp. nov. (holotype). B. S. (N.) illusor Ryvkin, 1987 (Russia: Amur Area: Angelokit River). C–H: S. (N.) latipennis J. Sahlberg, 1880. C. (Russia: SW Taimyr: Ladannakh Lake). D. (Russia: Taimyr: Kotuy River). E. (Russia: Putorana: Ayan Lake). F–G. (Russia: Evenkia: Kruten’kiy Stream). H. (Russia: Magadan Area: ‘Aborigen’). I–J. S. (N.) sphaerops Casey, 1884 (U.S.A.: New York: Albany Co.). K. S. (N.) melanopus Marsham, 1802 (Ukraine: Odessa Area: Krinichnoye). – Scales = 0.1 mm.