Sperchon setiger Thor, 1898

Martin, Peter, 2006, On the morphology and classification of larval water mites (Hydrachnidia, Acari) from springs in Luxembourg, Zootaxa 1138, pp. 1-44 : 12-13

Sperchon setiger Thor, 1898

Records: Sperchon setiger was not found in Luxembourgian springs, neither as larvae nor as adults, but was frequently recorded in running waters of the country and is known to invade spring habitats occasionally. Therefore, but also in view of the need to separate it from S. insignis (see below), it is treated here in detail.

Descriptions of larvae: Besseling (1939), Ullrich (1976), Wainstein (1980), Biesiadka & Cichocka (1984).

Material examined: Specimens were collected as parasites of simuliid pupae in the small stream of Ammer (Baden­Württemberg, southwest Germany) (August 2004, leg. R. Gerecke, Tübingen).

Description (unless otherwise indicated, n = 5): Habitus of the idiosoma moderately ovate; in non­engorged specimens and to a lesser extent also in engorged specimens, caudal idiosoma showing a small field with a transverse­folded integument ( Fig. 17 ). Size of idiosoma strongly varying: length/width in a non­engorged specimen 198/156µm, in five engorged specimens 313–531 (374)/260–454 (309).

Dorsal idiosoma ( Fig. 17 ): Dp relatively small, and finely striated. Anterior margin nearly straight or slightly concave, posteriorly vaguely confined. Length/width of Dp 85– 88 (86)/60–64 (61), Mp2­Amdp 36–41 (39), Mp1­Mp1 46–52 (48), Mp2­Mp 2 26–30 (28), Lp1­Lp1 37–42 (40), Lp2­Lp2 53–55 (54), Mp1­Lp 1 7–11 (9), Mp2­Lp 2 13–18 (16), Mp1­Mp 2 29–32 (30), Lp1­Lp 2 24–30 (26), Mp1 34–38 (36), Mp2 38–43 (40), Lp1 42– 47 (44), Lp2 47–58 (50), Hu 38–50 (42), Mh1 46–50 (48), Mh2 44–48 (47), Mh3 38–43 (41), Mh 4 30–35 (32), Lh1 35–50 (40), Lh2 38–41 (40), Lh 3 26–30 (28).

Ventral idiosoma ( Fig. 18 ): A small chitinous structure lies anterior of the setae V1, in some specimens being only poorly visible. Length/width CX­I 71–74 (72)/34–37 (36), CX­II 65–71 (68)/44–46 (45), CX­III 67–78 (71)/61–65 (63), chitin of the coxal plates is lacking a pattern and is probably smooth, urstigmata slightly elongated, maximal inner diameter 13–16 (14), C1­C2 37–41 (39), C1­posterior margin of CX­I 18–22 (19), C1­ Mmcp 18–20 (19), C4­Pmcp 60–72 (64), C 1 31–48 (36), C2 50–73 (58), C4 38–46 (36), length/width Expp 10–12 (11)/12–14 (13), E1­ E1 6 –7 (7), E2­ E 2 8 –11 (9), E 1 8 –22 (15), E 2 13 –25 (19), V 1 28–35 (30), V 2 23–29 (26), V 3 25–28 (26), V 4 22–26 (24).

Gnathosoma: Ventral base (n=2) 88–90 (89), length chelicera (n=3) 71–75 (73), height (n=1) 22, length chela (n=2) 19–22 (20), length/height P2 (n=1) 34/26, length/height P 3 19/25, claw 14.

Legs (n=5): Leg segments I­III­L3+4 and III­L5 with a little distinct lineation.

Leg I: Total length 238–251 (244), length/heigth I­L 1 31–35 (33)/25–26 (25), I­L2 37–38 (37)/25–26 (25), I­L3 50–53 (51)/23–25 (24), I­L4 53–55 (54)/22–24 (23), I­L5 66– 70 (68)/18–19 (19).

Leg II: Total length 248–271 (259), length/height II­L1 34–37 (35)/24–25 (24), II­L2 34–40 (37)/22–25 (24), II­L3 53–55 (53)/22–24 (23), II­L4 58–62 (59)/20–23 (21), II­L5 71–77 (74)/20–22 (21).

Leg III: Total length 316–340 (326), length/height III­L1 50–55 (52)/22–24 (23), III­ L2 44–49 (47)/23–24 (24), III­L3 70–72 (70)/22–23 (22), III­L4 73–78 (75)/22–23 (22), III­L5 78–85 (82)/18–19 (18).

Diagnostic characters of larvae: The most striking characters of Sperchon setiger are the absence of seta C3 on coxal plate II and the small dorsal plate.

Remarks: The former descriptions of larval Sperchon setiger agree well with the larvae presented here. A re­description is nevertheless necessary because additional measurements not given in the literature are needed for an accurate comparison between S. setiger and the related species S. insignis (see below). Furthermore, the larvae presented here derive from a population in which most larvae are parasites of pupal simuliids ( Renz et al. 2004), instead of parasitizing imagines of these dipterans, as is their usual behaviour ( Ullrich 1978; Martin 2000). Smith (1998) reports on morphological differences between larvae from populations with non­parasitic and parasitic behaviour. In this special case, however, no morphological differences between the larvae with different parasitic behaviour could be found.

Figures

FIGURES 15 – 20. Fig. 15: Sperchonopsis verrucosa, ventral idiosoma (from Martin 2000), Fig. 16: Sperchon clupeifer dorsal idiosoma (redrawn and modified after Ullrich 1976), Fig. 17: Sperchon setiger, dorsal idiosoma, Fig. 18: Sperchon setiger, ventral idiosoma and gnathosoma (from Renz et al. 2004), Fig. 19: Sperchon thienemanni, dorsal idiosoma, Fig. 20: Sperchon thienemanni, ventral idiosoma (Figs. 19 – 20 from Martin 2003).