Onychiurus wilchi Wray, 1950

Bernard, Ernest C., 2015, Redescriptions of Hypogastruridae and Onychiuridae (Collembola) described by David L. Wray, Zootaxa 3918 (3), pp. 301-338 : 335-336

Onychiurus wilchi Wray, 1950

Figs. 21 G–J

Onychiurus wilchi Wray 1950a: 98 ; Christiansen & Bellinger 1980: 404; 1998: 444, unplaceable; Pomorski et al. 2009: 1049, unplaceable.

?= Onychiurus formosanus Denis, 1929 in Stach 1954: 62.

Specimens examined. Lectotype, sex undetermined, and three paralectotypes (by present designation, labeled as cotypes), USA, Illinois, Highland, 7 June 1946, garden soil, B. T. Wilch, coll.

Wray’s (1950a) description, condensed. Length up to 1.5 mm. Color white. Postantennal organ with 18–20 compound vesicles at right angle to long axis. Sense organ of Ant. III with 5 papillae, 5 guard setae, 2 sense rods, 2 sense clubs [illustrated as smooth and curved]; Ant. IV with 10–12 curving olfactory hairs. Pseudocellar formula 32/022/02233; each precoxa [= subcoxa 1] with one pseudocellus. Unguis untoothed, unguiculus tapering to a fine filament reaching tip of unguis. Two stout, nearly straight anal spines, two-thirds the length of the unguis. Long curving setae at posterior end of abdomen. Clothing of scattered long straight setae, sparse short setae, and a few minute strongly curved setae. Cuticular tubercles coarse.

Reexamination. Granulation indeterminable; nearly all setae invisible. Sense clubs of Ant. III stalked, bent, smooth to possibly slightly roughened ( Fig. 21 I). Maxilla ( Fig. 21 G) with prominent bifurcated lamella 1 extending past capitulum teeth, lower arm with long, thin denticles on one side; lamella 2 reaching teeth, denticles longer on one margin than on other; lamellae 4 and 5 rounded, covered with minute denticles; denticles of lamella 6 all appearing to be in apical region. Sensilla A and B of labial palpus with rounded tips, other sensilla pointed (AB type). Hind tibiotarsus with 7 setae in proximal whorl, 9 setae in distal whorl ( Fig. 21 J); unguiculus tapering to fine filament nearly reaching tip of unguis. Furcal area invisible. Anal spines stout, straight, almost two-thirds length of unguis. Seta p0 present on abdominal tergite VI ( Fig. 21 H).

Additional information. Pronotum with 1+1 dorsal pseudocelli, Abd. I with 3+3 dorsal pseudocelli (Soto- Adames 2013), thus making the pseudocellar formula 32/122/32233, not including subcoxal pseudocelli.

Remarks. Pomorski et al. (2009) felt that O. wilchi most probably belonged in Onychiurus s. str. but that the characters described and illustrated by Wray (1950a) were insufficiently accurate for definite placement. The four specimens examined appear to have all been in ecdysis when collected and proved to be nearly featureless both before and after remounting. The few characters that could be discerned, along with the parts of Wray’s description that are likely to be reasonably accurate, do allow for placement of the species in Onychiurus s. str. Most significantly, the molted labial palpi were still attached to the head of one of the specimens and clearly showed blunt A and B sensilla, and pointed C, D, and E sensilla. This arrangement is found only in Onychiurus s. str. and several species transferred to the related genera Deuteraphorura Absolon, 1901 and Orthonychiurus Stach, 1954 (Bellinger et al. 1996-2014, Fjellberg 1998, Pomorski 1998).

Onychiurus wilchi was considered a possible synonym of O. formosanus by Stach (1954), a species transferred to Formosanochiurus Weiner, 1986 ( Weiner 1986, 1996). Formosanochiurus was differentiated by chaetotaxy ( Weiner 1986) and by the presence of an apical vesicle on Ant. IV ( Weiner 1996). The condition of the O. wilchi specimens is too poor to determine whether they are similar to F. formosanus . Arbea (2012) did not consider Formosanochiurus spp. to belong in Onychiurus and excluded them from his analysis of Onychiurus .

Christiansen & Bellinger (1980) suggested that O. reluctus Christiansen, 1961 could be a synonym of O. wilchi , and Pomorski et al. (2009) thought it possible that O. steinmanni Pomorski, Furgoł & Christiansen, 2009 could also be O. wilchi . Soto-Adames (2013) examined a type specimen of O. wilchi in the Illinois Natural History Survey, Champaign, Illinois, USA, and detected pronotal and Abd. I pseudocelli. The presence of 1+1 pronotal pseudocelli eliminates O. steinmanni as a possible synonym. The fact that Wray missed these pseudocelli suggests that numbers for some of the other segments could be wrong, as well; but if Wray’s counts of 2+2 pseudocelli on Abd. II and III are correct, these numbers would serve to separate O. wilchi from other North American Onychiurus spp. In addition, O. wilchi was described and illustrated as having 18–20 vesicles in the PAO, whereas none of the Onychiurus spp. in Pomorski et al. (2009) has more than 17 vesicles in the PAO. Thus, it appears that O. wilchi may be a recognizable species and that it is premature to synonymize any of these species. In the key of Pomorski et al. (2009) O. wilchi should trace to O. steinmanni , but may be separable from that species by the number of compound vesicles in the PAO and pseudocelli on the thoracic terga.

If O. wilchi is assumed to have 1+1 pseudocelli on Th. I and 3+3 pseudocelli on Abd. I as observed by Soto- Adames (2013) but otherwise follows Wray’s observations, then O. wilchi will key to O. polychaetosus Lee & Park, 1986 in the Onychiurus key of Arbea (2012). The two species differ in sense club architecture, with O. wilchi having smooth or slightly roughened clubs and O. polychaetosus having granulated clubs.

Figures

FIGURE 21. Onychiuridae. A – C) Leeonychiurus mai. D – F) Heteraphorura magnina. G ‒ J) Onychiurus wilchi. A, D, G) Maxillae. B, E, H) Dorsal terminus of sixth abdominal segment. C, F) Venter of sixth abdominal segment. I) Sense organ of third abdominal segment, sense clubs not shown. J) Distal part of hind tibiotarsus.