Ropohalacarus pallidus Bartsch, 2013

Bartsch, Ilse, 2018, Freshwater halacarid mites (Acari: Halacaridae) from Madagascar - new records, keys and notes on distribution and biology, Bonn zoological Bulletin 67 (2), pp. 79-99 : 90-94

Ropohalacarus pallidus Bartsch, 2013

Ropohalacarus pallidus Bartsch, 2013b: 80–84 , figs 1a– h, 2a–g.

Collecting data. Central Madagascar, Antananarivo, Anjazorobe, River Ranonisoanavola (larger stream E from main mountain chain), 1200 m asl, 13.2°C, 0.058 mS/ cm, interstitial, 23 Jul. 2001 ( MD 012 ) . South-eastern Madagascar, Fianarantsoa, Ionilahy, stream draining area Marosaro (S from River Ionilahy ), 220 m, 21°C, 0.072 mS/cm, 12 Aug. 2001, interstitial ( MD 023 ) . – South-eastern Madagascar, Fianarantsoa, Ionilahy , small stream crossing the railroad east from village, 200 m, 15 Aug. 2001 ( MD 027 ) . – South-eastern Madagascar, Fianarantsoa, Andrambovato , stream 3 km E from the village, upstream from the cascade, 900 m, 20 Aug. 2001 ( MD 038 ) . – Southern Madagascar, Tulear, Tsimelahy , River Antarantsa , ca 1 km upstream from village, 300 m, 20.4°C, 0.171 mS/cm, 04 Sep. 2001, interstitial ( MD 058 ) . – Tulear, Andohalela, Isaka , spring area S pass RIP 118 (km36), 700 m, 16.0–18.4°C, 0.055 –0.060 mS/cm, 10 Sep. 2001, interstitial ( MD 071 ) . – Northern Madagascar, Antsiranana, Andapa, right affluent River Am- bendrana downstream, large cascade, 600 m, 11 Nov. 2001 ( MD147 ) .

Short description ( Fig. 8A–G ). Female: Length 203–245 [30] µm, idiosoma pale, about 1.8 times longer than wide, its anterior and posterior part narrowed. Eye pigment lacking. AD and PD fused to an elongate dorsal shield ( Fig. 8A ). Ventral shield extending dorsad and including AE, PE, GA ( Fig. 8B ) and parts corresponding to OC. Integument of dorsal shield with delicate porosity and faint foveate ornamentation, ventral plates almost smooth. Dorsal setae very small, ds-1, ds-3 and ds- 4 in dorsal shield, ds- 2 in dorsal part of ventral shield. Adanal setae lacking. Gland pores lacking. Area of ventral shield 92 Ilse Bartsch

representing AE with two pairs of marginal and one pair of ventral setae, areas of PE each with one marginal and one ventral seta, and that of GP with two perigenital setae. Marginal setae of idiosoma longer than ventral setae. Three pairs of genital acetabula arranged in posterior part of genital sclerites. Gnathosoma slightly wider than long ( Fig. 8C ). Palps four-segmented, extending beyond short, conical rostrum. Short palps and rostrum visible in dorsal aspect. Legs distinctly shorter than idiosoma (length ratio leg I:idiosoma equalling 0.5:1). Distance between apertures of pairs of legs II and III almost equal to half the length of idiosoma (in the other genera length of idiosoma more than twice the distance between these apertures). Trochanter I in one of the females studied with delicate medial seta, in general no seta present. Ventral setae on genu I and three ventral setae on tibia I bipectinate ( Fig. 6D ).

Male: Not present.

Juveniles: Length of deutonymph 173–226 µm [6], of protonymph 122–173 µm [3], of larva 113–128 µm [2]. Nymphs with AD and PD separated by striated integument, remnants of ocular plates and marginal part of epimeral plates fused. Ventral plates AE, PE and GP fused to a single ventral shield, no fissure between area represent- ing AE and GP. Ventral plates delicate; ornamented with foveae. In both nymphal instars area representing AE with three pairs of setae ( Fig. 8E and F ). In deutonymph area representing PE with one pair of marginal and one of ventral setae ( Fig. 8F ) and area of GP with one pair of pgs. Protonymphal PE solely with pair of marginal setae. Larval tarsus III, just as tarsi III of following instars, with three dorsal setae, namely two fossary setae and one solenidion ( Fig. 8G ).

Biology. Of 32 females studied 13 (41%) were ovigerous. In general a single egg was present, its size (length x diameter) between 45 x 43 µm and 70 x 43 µm.

Remarks. As illustrated in Bartsch (2013b: fig. 2e), AD and PD of the deutonymphs, as also those of the protonymphs, are separated from each other by a narrow, transverse area of striated integument, but both deuto- and protonymphs have a ventral shield, including the anterior and posterior epimeral and the genital plate (AE, PE and GP). In contrast to Bartsch (2013b: fig. 2f, 2g), no transverse rupture was recognized in the new material studied (three deutonymphs, one protonymph). In the majority of halacarids the adults have solid exoskeletal plates. In several species these are fused to a dorsal or ventral shield. Sometimes, though rarely, both the dorsum and venter are covered by a solid shield whereas the juveniles have the plates separated by tensible striated integument. Consequently juveniles can grow due to ex- pansion of the striated integument between the dorsal and the ventral plates (as illustrated in Halacarellus subterraneus — Bartsch 1972 fig. 28A, B versus C, D and E, F versus G, H) whereas the adults can hardly increase in size. An exception is Ropohalacarus pallidus . In the juveniles of this species, the foveate textured integument of the ventral plates is expected to allow a slight dilatation (cf. Bartsch 2013b). Data on the thickness of the pro- and epicuticula are lacking.

No males have ever been found, neither of Ropohalacarus pallidus nor of the second species, namely R. uniscutatus , but the number of specimens studied to date is small (<50 individuals).

Compared with other Madagascar halacarids, R. pallidus is in its general shape most similar to Porohalacarus alpinus . Distinguishing characters are: the pale idiosoma (versus prominent spots of eye pigment), the dorsal and ventral shield (versus dorsum with AD, OC and PD, venter with AE, PE and GP), the ornamentation of dorsal shield or plates, delicately foveate versus reticulated with longitudinal polygons, the position of apertures of legs III, in posterior third of idiosoma (0.7) versus in its middle (0.5).

Geographical Distribution ( Fig. 9 ):

Afrotropical Region. – Madagascar ( Bartsch 2013b and present record).

Figures

Fig. 8A–G. Ropohalacarus pallidus Bartsch, 2013.A. idiosoma, dorsal, female; B. idiosoma, ventral, female; C. gnathosoma, ventral, female; D. leg I, medial, female; E. idiosoma and gnathosoma, ventral, protonymph; F. idiosoma, ventral, deutonymph, G. leg III, lateral, larva. (Scale = 50 µm) (pgs, perigenital seta(e); P-1, first palpal segment; III-1, III-2+3, III-4, III-5, III-6, trochanter, femur, genu, tibia and tarsus of leg III).

Fig. 6A–G. Porohalacarus alpinus (Thor, 1910). A. idiosoma, dorsal, female; B. idiosoma, ventral, female; C. gnathosoma, ventral, female; D. gnathosoma, dorsal (P-3 and P-4 omitted), female; E. leg I, medial, female; F. idiosoma, ventral, male; G. papilla with genital acetabula, male. (A–F, scale = 50 µm, G, scale = 10 µm) (ch-cl, cheliceral claw; ch-f, dorsal flap-like process of chelicera; co, cornea; eyp, eye pigment; pap+gac, papilla with genital acetabula; P-1 to P-4, first to fourth palpal segment; ret-a, reticulate area; vs, ventral seta).

Fig. 9. Records of Ropohalacarus pallidus Bartsch, 2013 (black spot) and R. uniscutatus Bartsch, 1982 (asterisk).