Sperchon (Hispidosperchon) denticulatus

Martin, Peter, 2016, Larval morphology of benthic and interstitial water mites (Acari: Hydrachnidia) from a Luxembourgian stream, Zootaxa 4139 (4), pp. 451-480 : 454-455

Sperchon (Hispidosperchon) denticulatus -gr.

Diagnosis. Characters as in the family. CX-II bearing one seta, Dp relatively small and narrow, setae of dorsal idiosoma relatively long.

Material examined. Larvae reared from females from the river Our in Luxemburg, where the abundant presence of the species was known by own unpublished data. Characters of 5 larvae were measured.

Description. Habitus of the idiosoma moderately rectangular, distinctly longer than wide. Dorsal L idiosoma 211–234 (224), W 156–169 (162). In unengorged specimens integument smooth with the exception of a small posteriormedial part of the ventrum which bears rough wrinkles.

Dorsal idiosoma ( Fig. 1 A): Dp elongated, about two times longer than wide, caudally tapering, covering about a quarter of the dorsal idiosoma in unengorged larvae, acutely lineated. L Dp 140–151 (147), W 70–75 (73), L of common eye capsule 31–34 (32), Mp2-Amdp 44–49 (47), Mp1-Mp1 36–39 (38), Mp2-Mp 2 29–34 (30), Lp1-Lp 1 21–26 (22), Lp2-Lp2 52–62 (59), Mp1-Lp 1 8–10 (10), Mp2-Lp 2 26–29 (28), Mp1-Mp2 36–39 (37), Lp1-Lp 2 23– 26 (25). Setae Hu, Mp, Lp and the first setae Lh relatively long, making the habitus look “shaggy”. Mp1 34–36 (35), Mp 2 31–34 (33), Lp1 83–94 (88), Lp2 135–148 (139), Hu 101–114 (109), Mh1 114–125 (119), Mh2 117–125 (121), Mh3 109–120 (112), Mh4 62–68 (65), Lh1 101–109 (108), Lh2 96–107 (100), Lh3 70–78 (73).

Ventral idiosoma ( Fig. 1 B): CXIII distinctly larger than other coxal plates. In some specimens a small chitinous structure lies in between the alveoli of setae V1. CXII only slightly longer than wide. L CXI 75–81 (79), W 36–42 (40), L CXII 75–83 (80), W 55–60 (57), L CXIII 83–91 (86), W 73–83 (76), max. diameter of urstigma 18–21 (19), C1-C2 44–47 (46), C1-Pmcp 21–26 (24), C1-Mmcp 21–23 (21), C4-Pmcp 70–78 (74), C1-C4 44–52 (48), C1 44–49 (47), C2 62–78 (72), C3 75–96 (82), C4 57–73 (66). Expp squarish with concave sides, Exp longish. L Expp 13–16 (14), W 13–16 (14), E1-E1 5–8 (7), E2-E 2 10–13 (11), E 1 5–16 (9), E 2 8–18 (14), V1 52 – 62 (57), V2 60 –65 (62), V3 60 –81 (69), V4 55 –78 (69).

Gnathosoma (measurements from ventral view): base 99–104 (100), L chelicera 55–73 (61), chela 16–18 (17), two long setae inserted on PV distinctly longer than the others, L 127–156 (141) and 107–120 (113), respectively.

Leg I ( Fig. 1 C): total L 270–286 (278), L IL-1 (1se) 31–36 (33), IL-2 (7se) 44–47 (45), IL-3 (4se, 1so) 60–62 (62), IL-4 (9se, 1so) 65–68 (67), IL-5 (13se, 1so) 70–73 (71), H IL- 1 26–29 (28), IL- 2 29–31 (29), IL- 3 26–29 (27), IL- 4 21–26 (23), IL- 5 18–21 (19).

Leg II ( Fig. 1 D): total L 278–307 (288), L IIL-1 (1se) 34–39 (35), IIL-2 (7se) 47–60 (50), IIL-3 (4se, 1so) 57– 60 (59), IIL-4 (9se, 2so) 68–73 (70), IIL-5 (13se, 1so) 73–75 (74), H IIL- 1 26–31 (28), IIL- 2 26–29 (28), IIL- 3 23– 26 (25), IIL- 4 21–23 (22), IIL- 5 18–21 (19).

Leg III ( Fig. 1 E): total L 36 1–390 (378), L IIIL-1 (1se) 55–65 (61), IIIL-2 (6se) 55–60 (58), IIIL-3 (4se, 1so) 78–83 (81), IIIL-4 (9se, 1so) 94–96 (94), IIIL-5 (13se) 81–86 (83), H IIIL-1 2 6–26 (26), IIIL- 2 26–26 (26), IIIL- 3 21–23 (22), IIIL- 4 21–23 (22), IIIL-5 1 8–21 (20).

Remarks. To date, two descriptions of the larval Sperchon denticulatus have been published. Sparing (1959) and Ullrich (1976) gave some illustrations and measurements of S. denticulatus which resembled the here described larva remarkably but were also different in some details. For example, Sparing’s length/width dimensions of the dorsal plate (156/72 µm) are almost exactly the same as in the present study (mean 147/73 µm). But, probably due to limitations in optical equipment, Sparing described a lack of the excretory pore plate. In the Ph.D. thesis of Ullrich (1976) the affiliation to S. denticulatus was not clear but also resembled the larva here described. The key characters described above seem to be unique within the genus.

Since only females were found in the Lurenzgriecht, the definite status of the present species has to remain open and was therefore given as S. denticulatus -group. Three species are included in the complex where only the rarely occurring males are identifiable (see Di Sabatino et al. 2010): Sperchon (Hispidosperchon) denticulatus Koenike, 1895 , Sperchon (Hispidosperchon) hibernicus Halbert, 1944 and Sperchon (Hispidosperchon) vaginosus Thor, 1902 . All known males from Luxembourg belong to S. vaginosus (R. Gerecke, pers. comm.) which may enable to define the specimens treated here as S. cf. vaginosus .

Characters that enable the taxonomic separation of larvae of the S. denticulatus -group from the other Sperchon species treated here are, for example, the strong lineation of the leg segments, the relatively small Dp (length/width mostly> 1,5) or the extensive length of many dorsal setae (> 100 µm). Last character was also mentioned by Müller (2015) who illustrated the larva of S. denticulatus from Saale river without a well-defined Expp.

Figures

FIGURE 1. Sperchon denticulatus, larva. A. dorsal idiosoma, B. ventral idiosoma, C. IL, D. IIL, E. IIIL. Scale bars 100 µm.