Sperchon fuxiensis Zhang, 2017

Zhang, Xu, Hou, Xue, Li, Guang, Mu, Rong-Rong & Zhang, Hai-Jun, 2019, With DNA barcoding revealing sexual dimorphism in a water mite: the first description of male Sperchon fuxiensis (Acari: Hydrachnidia: Sperchontidae), Zootaxa 4560 (2), pp. 385-392 : 387-388

Sperchon fuxiensis Zhang, 2017

Figures 1–9

Material examined. 2 males, Anhui Province, Fuxi village, Monkey Valley scenic area, an unnamed stream (30°04′15″N; 118°09′26″E), 11 November 2017, coll. Xu Zhang.

Description. Male (n=2): Idiosoma flat and oval, 627 (682) in length, 523 (584) in width. Integument yellow in colour, marked with reticulate pattern ( Fig. 2 ). A1 short and thick, other dorsal setae relatively thin and long.Chitinous plates and glandular plates on dorsum extremely developed, almost occupied all the space. ( Fig. 1 ). The chitinous plates and glandular plates on the venter relatively small ( Fig. 3 ). Coxae in four groups. Anterior coxal plates close to each other but not fused medially. Posterior groups of coxae widely separated. ACG 158 (172) in length, apodeme well developed, and a little covered with CxIII. E2 laterally between ACG and PCG. PCG 234 (255) in length. E4 absent from Cx?. Distance between anterior end of ACG and posterior end of PCG 403 (440). Genital field between CxIV with a small platelet in front, 146 (151) in length, 142 (150) in width. Pre- and postgenital sclerites small. Three pairs of genital acetabula, the first pair of genital acetabula somewhat triangular, the second pair elliptical, the third pair rounded and larger than the anterior two pairs. V1 on small sclerites and without accompanying glandularia. Excretory pore between V2, and with a sclerotized ring.

Capitulum with a long rostrum, length 230 (234). Chelicera total length 212 (220), basal segment length 158 (163), claw length 54 (57), ratio of basal segment /claw length 2.9. Dorsal lengths of the palp segments: P-I, 22 (23); P- II, 123 (127); P-III, 172 (178); P-IV, 178 (183); P-V, 36 (37). P-I without seta. P-II with a long ventro-distal projection bearing a long seta and a short seta, the lateral and dorsal of P-II with about eleven short and smooth setae and none of them plumose. The ventral side of P-III nearly straight and without seta, four short smooth setae on the lateral and dorsal side. P-IV with two small peg-like ventral setae, of which one larger almost in the middle, another one near the ventral distal end.

Legs. Dorsal lengths of leg I: I-L-1, 54 (55); I-L-2, 59 (63); I-L-3, 63 (70); I-L-4, 125 (132); I-L-5, 120 (123); I-L-6, 123 (129). Dorsal lengths of leg IV: IV-L-1, 63 (87); IV-L-2, 111 (119); IV-L-3, 114 (132); IV-L-4, 220 (225); IV-L-5, 194 (203); IV-L-6, 168 (187). Third to fifth segments of leg I-IV with rather short plumose setae in longitudinal rows ( Fig. 9 ). Ambulacrum with two claws. Each claw with claw blade well protruding, bearing a long dorsal and a shorter ventral clawlet. ( Fig. 7 ).

Remarks. Sexual dimorphism of morphology is very common in the genus Sperchon , but the differences between male and female are usually small. Contrast the males in our study with the females of S. fuxiensis (see detail in Ding et al. 2017), the chitinous plates and glandular plates of the males were much developed than the females, especially the sclerotization almost occupied the whole dorsum. If many small characters such as the pattern of integument, excretory pore with a sclerotized ring and the shape of palps were ignored, the male would have probably been identified as a species other than S. fuxiensis .

This taxonomic confusion was clarified using DNA barcoding technology which confirmed that males were indeed S. fuxiensis and that the species showed strong sexual dimorphism, a rare occurrence in the genus Sperchon . Some minor differences between males and females were also found in the number of the setae on the palps and legs which we regarded as insignificant.

Figures

FIGURES 1–3. Sperchon fuxiensis, Male. 1. idiosoma, dorsal view; 2. decoration pattern of integument; 3. idiosoma, ventral view.

FIGURES 4–9. Sperchon fuxiensis, Male. 4. infracapitulum; 5. chelicera; 6. palpal; 7. claw; 8. IV-L-1–IV-L-6; 9. dorsal seta of IV-L-4.