Xenylla duchesnea Wray, 1958

Bernard, Ernest C., 2015, Redescriptions of Hypogastruridae and Onychiuridae (Collembola) described by David L. Wray, Zootaxa 3918 (3), pp. 301-338 : 328-330

Xenylla duchesnea Wray, 1958

Fig. 18

Xenylla duchesnea Wray 1958: 10 ; Christiansen & Bellinger 1980: 220; 1998: 234.

Specimens examined. Lectotype female (labeled “ type ” on slide) (by present designation), one paralectotype juvenile on slide, numerous paralectotypes in ethanol, USA, Utah, Duchesne, 27 March 1956, juniper litter, G. F. Knowlton & H. F. Thornley, colls.

Redescription. Body length 1.09 mm [up to 1.0 mm]. [Body with white background covered with lacework of purplish pigment and many round spots]. All typical setae short, sensillum-like setae more than twice the length of neighboring setae ( Fig. 18 A); chaetotaxy slightly asymmetrical on head, mesonotum, and metanotum. Head with three sd-row setae (lacking sd1, sd2); seta c2 absent; V-row setae absent or represented by a single v1 seta; lengths of setae l1 and l3 approximately equal. Head ventrally with a1–a3, m1–m3, p1 and p5 setae ( Fig. 18 B). Pronotum with 3+3 setae of approximate equal length. Mesonotum and metanotum with seta a5 (= la2 of Gama), without setae m2 and m5; seta p2 anterior to other p-row setae, sensillum-like seta p4 posterior to other p-row setae. Mesothoracic and metathoracic sternites without setae. Abdominal tergites I–III with all anterior and posterior setae, m-row setae absent. Tergite IV with three m-row setae (m1, m3, m5); seta p4 slightly advanced anteriorly from other p-setae. Abdominal sternite II with setae a5, m5 and p1–p6, seta p3 longer than the others ( Fig. 18 C); sternite III with setae a5, a6, m3 and p1–p6, seta p3 longer than the others; sternite IV with 3 a-setae ( Fig. 18 H), 3 m-setae; p1 absent, p2–p4 present.

Antennal segment IV with simple granulate apical bulb, four stalked, conical sensilla, minute peg-like organite, and slender, tapering microsensillum ( Fig. 18 E); most dorsal setae sensilliform, narrowly rounded at tip; one normal seta proximal to microsensillum; apically one small sensilliform seta and two short normal setae. Ventrally, Ant. IV without distinct sensory field but with 11 short, pointed setae surrounding a sensilliform seta; subapically and apically, one hooked and one curved sensilliform setae along with four short, straight sensilliform setae ( Fig. 18 F). Sense organ of third segment consisting of two short, rounded sensilla flanked by more linear sensilla on each side ( Fig. 18 E); microsensillum minute, peg-like, not in pit ( Fig. 18 E). First antennal segment with 7 setae, Ant. II with 12 setae.

Ocelli 5+5. Labrum anteriorly with four rounded papillae and smooth, convex anterior edge, setal formula 5-5- 4. Maxilla head not clearly seen. Outer lobe of maxilla with two sublobal hairs. Labial palpus ( Fig. 18 D) with slender, straight sensilla A–E; guard setae a1, b1, b2 and d2 rounded at apex; guard setae b3, b4, d3 and e3 curved, pointed, shorter than sensilla except e3 length equal to sensillum E; other guard setae absent.

Tibiotarsi I, II, III with 19, 19, 18 setae, respectively, each with two dorsal clavate tenent hairs reaching ungual tip; lateral and inner teeth absent; unguiculus absent ( Fig. 18 G). Ventral tube with 4+5 setae. Tenaculum with 2+2 teeth, without setae. Furcula weakly developed, all parts fused ( Fig. 18 H); mucro represented by minute sclerotization at tips of the dens; each dens with one fine seta, manubrium with 3+3 setae (a1–a3). Anal spines minute, slender, conical, tapering evenly, less than half the length of inner unguis.

Remarks. This examination of X. duchesnea types yielded differences with Wray’s description and illustrations, especially in the shape of the antennal sensilla, fusion of dens and mucro, and shape of the anal spines ( Wray 1958: p. 10). Wray drew four linear sensilla near the tip of a densely setaceous Ant. IV, interpreted the dens and mucro as separate and equal in length, and drew the mucro with a small inner lamella; the drawing of the anal spines shows two very slender, almost linear anal spines extending past the end of Abd. VI. Christiansen & Bellinger (1980, 1998) were not able to examine X. duchesnea type specimens, but rather based their interpretation and illustrations of the species on specimens from another locality, Blacksmith Fork Canyon (given in Christiansen & Bellinger (1980, 1998) as Blacksmith Canyon). This site is near Logan, Utah, about 225 km from Duchesne, Utah, the type locality. Examination of the lectotype clearly showed that the Ant. IV sensilla are stalked and conoid, dens and mucro are fused, and the mucro is reduced to a small terminal sclerotization. The anal spines were more substantial than illustrated by Wray, and dissimilar to those from Blacksmith Fork Canyon, which were illustrated as aristate. Finally, the Abd. III–IV ventral chaetotaxy of the Blacksmith Fork Canyon specimen sketched in Christiansen & Bellinger (1998, p. 234), although not easy to interpret, appears to differ from that of X. duchesnea . Therefore, the specimens observed by Christiansen & Bellinger (1980, 1998) may well represent an undescribed species.

In the key of Thibaud et al. (2004) X. duchesnea traces to couplets 23–24, which include X. canadensis Hammer, 1953 , X. duchesnea and X. babenkoi Stebaeva & Potapov, 1994 . This placement was dependent on an inaccurate illustration of the mucro by Wray (1958). As redescribed here, X. duchesnea keys to X. caudata Jordana, 1993 in Thibaud et al. (2004) if the dens is considered to be papilliform and if the mucro is considered to be absent. In X. duchesnea head seta l1 is longer than l3, Ant. IV has four sensilla and a minute mucronal element is present (in X. caudata seta l1 is shorter than l3, Ant. IV has five sensilla and the mucro is entirely absent).

Figures

FIGURE 18. Xenylla duchesnea, lectotype. A) Dorsal chaetotaxy. B) Ventral cephalic chaetotaxy. C) Ventral chaetotaxy of abdominal segments II ‒ V. D) Labial palpus. E) Third and fourth antennal segments, dorsal view. F) Third and fourth antennal segments, ventral view. G) Foretibiotarsus, dorsal view. H) Retinaculum and furcula.