Limnohalacarus, Walter, 1917

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 : 82-84

Limnohalacarus novus Bartsch, 2013

L. novus Bartsch, 2013a: 206–210, figs 3a–h, 4a–g. L. billabongis, Bartsch 2008b: 127 , 128.

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, interstitial, 12 Aug. 2001 ( MD 023 ) . – South-eastern Madagascar, Fianarantsoa, Ionilahy, River Ionilahy , 200 m, 23°C, 0.059(11. Aug.)–0.088(13. Aug.) mS/cm, interstitial, 11/ 13 Aug. 2001 ( MD 026 ) . – South-eastern Madagascar, Fianarantsoa, Ionilahy, small stream crossing the railroad east from village, 200 m, 19.9°C, 0.083 mS/cm, 15 Aug. 2001 ( MD027 ) . – Southern Madagascar, Tulear, Tsimelahy, River Antarantsa , ca 1 km upstream from village, 300 m, 20.4°C, 0.171 mS/cm, interstitial, 04 Sep. 2001 ( MD 058 ) . – Central Madagascar, Antanarivo, Ankaratra, Reserve Manjakatompo, left affluent of River Mahiavona , EM Mantsina, 1750 m, 14.1°C, 0.003 mS/cm, interstitial, 08 Oct. 2001 ( MD107 ) . – North-western Madagascar, Majunga, Adjamangirana, stream in dry forest, upstream, rice field area (road to the village of Tsaratanana), 220 m, 30.8°C, 0.008 mS/cm, interstitial, 19 Oct. 2001 ( MD115 ) . – Northern Madagascar, Antsiranana, Antalaha, Marofinaritra, River Ant- sohibe, upstream confluence with River Ankavia (5 km NE Amparihimena), 70 m, 25.2°C, 0.008 mS/cm, riffle, 03 Nov. 2001 ( MD135 ) . – Northern Madagascar, Antsiranana, Antalaha, Marofinaritra, River Andranomenaheli, upstream confluence with River Ankavia (right affluent below MD 135 ) , 70 m, 22.3°C, 0.009 mS/cm, riffle, 04 Nov. 2001 ( MD136 a). – Northern Madagascar, Antsiranana, Maroambihy (Sambava), left affluent of River Lo- koho upstream from the village, 90 m, 26.0°C, 0.010 mS/ cm, interstitial, 12 Nov. 2001 ( MD149 ) . – Northern Madagascar, Antsiranana, Joffreville (M. d’Ambre), River Antomboka , downstream large cascade, 850 m, 20 Nov. 2001 ( MD163 ) . – Northern Madagascar, Antsiranana, Joffreville (Montagne d’Ambre), River Manques in Re- serve Fontenay, 580 m, interstitial, 21 Nov. 2001 ( MD 165 ) .

Short description ( Fig. 3A–G ). Female: Length 206– 289 µm [20]. OC including platelet with glp-3 ( Fig. 3A ), L:W of OC 1.4–1.6:1. Length ratio of PD:AD 2.6–2.7:1. Pair of ds-2 absent. Ventral plates AE, PE and GP fused ( Fig. 3B ). Area corresponding to GP with three pairs of pgs, five to six pairs of gac and on each genital sclerite two (three) sgs. Ovipositor short and narrow (LxW 74 x 10 µm), very faintly sclerotized, genital spines very delicate and short, 2 µm in length, and arising from minute papillae ( Fig. 3D ). Anal slit less than 10 µm long and guarded by pair of short anal sclerites. Gnathosoma about 1.1 times longer than wide. Pair of mxs-2 shorter but wider than mxs-1 ( Fig. 3E ). Legs shorter than idiosoma, length ratio leg I:idiosoma 0.7:1. Length of telofemur I 2.1–2.3 times the height ( Fig. 3F ). Tibiae I to IV with 8, 7, 7, 6 setae [14]. Ventromedial seta on tibia II and both ventromedial setae of tibia III bipectinate; setae on legs I and IV smooth. Claws I to IV with J-shaped arranged pectines ( Fig. 3G ), extending from apical lateral flank and along medial flank to basis of claw. On claws II to IV basal tines partly fused to a lamellar process.

Male: Not present.

Juveniles: Length of deuto-, protonymphs and larvae 231–275 µm [13], 180–226 µm [7] and 142–170 [5] µm, respectively. In contrast to adults, OC and posteri- or gland-bearing platelet separated by transverse striae. Ventral plates AE, PE and GP of nymphs separated from each other by striated integument, in larvae GP absent and AE with pair of epimeral pores.

Biology. Eleven of 15 females studied held an egg. The length x width of the eggs ranged from 35 x 35 to 100 x 50 µm. The eggs are not deposited in the substratum but attached to tibiae IV. One-third of the females had a single cocoon fixed with a slender stem, the latter 2–3 µm wide. The length of the cocoons was about 103–113 µm, the diameter 60–64 µm. Each one enclosed a single embryo.

Limnohalacarus species have the excretory material accumulated within an ovoid, compressed body (cf. Walter 1914; Petrova 1966; Ramazotti & Nocentini 1960; Pepato & Dos Santos 2015). In the material studied, 11 (73 %) of 15 females, 9 (22%) of 27 deutonymphs and one (22%) of six protonymphs held such a body, but none of four larvae. The body was dorsal to the gut, in some individuals it had a dark centre, surrounded by concentrically arranged more or less transparent layers ( Fig. 3C ). In one female the excretory body was almost uniformly dark, in another one hyaline, the body recognizable mainly because refraction of light. In one female (length 255 µm) this body was 108 µm long, 71 µm wide and 41 µm thick, the general size range in length was 95–158 µm, in width 50–92 µm. The length of the excretory body equalled 0.4–0.5 times the length of the fe- male idiosoma. In deutonymphs the stratified body was 60–85 µm long, 45–95 wide, in a protonymph 50 µm long, 36 µm wide, i.e., a length of 0.3–0.4 and 0.2 of that of the nymphal idiosoma, respectively. Such a body was present/absent independent of the age of the instar, e.g. it was absent both in assumedly recently hatched females and in ovigerous ones and also in those carrying a cocoon (or their remnants) fixed to the tibiae.

Remarks. Adults of Limnohalacarus cultellatus and L. novus, the two species known from Madagascar, can easily be separated by (1) the shape of the ocular plates, namely OC hardly longer than wide (L: W 1.1:1) and not including the platelet with a gland pore versus OC 1.3 times longer than wide and including the platelet with gland pore, (2) the ventral plates, separated versus fused to a shield, (3) the length of the gnathosoma, at least 1.5 times longer than wide versus 1.1 times or less, and (4) the claws on tarsus I, with few delicate versus numerous long tines. Juveniles of both species have the ventral plates and the OC and gland-pore bearing platelet separated but can be distinguished by the shapes of gnathosoma and claw I.

Compared with African species, L. novus turns out to be most similar to L. portmanni . Both are of about the same size, their length 206–289 and 217–289 µm, respectively, but the PD of L. novus is not as slender as in L. portmanni and the length ratio PD:AD is 2.6–2.7: 1 in L. novus but 3.1–3.3: 1 in L. portmanni ( Bartsch 2013a) .

Geographical distribution ( Fig. 2 ) (cf. Bartsch 2013a): Afrotropical Region. – Madagascar; Australian Region. – Australia (Queensland – Moreton

Bay, North Stradbroke Island, not Moreton Island ).

Figures

Fig. 3A–G. Limnohalacarus novus Bartsch, 2013, female. A. idiosoma, dorsal; B. idiosoma, ventral; C. excretory body, ventral; D. genital area with ovipositor; E. gnathosoma, ventral; F. leg I, medial; G. claw I, ventral. (A–F, scale = 50 µm; G, scale = 10 µm) (dgr, dark granules; hy, hyaline part; mxs-1 and mxs-2, basal and apical maxillary seta, respectively; ov, ovipositor; ph, pharyngeal plate; P-3, third palpal segment; sgs, subgenital seta).

Fig. 2. Records of Limnohalacarus cultellatus Viets, 1940 (black spot) and Limnohalacarus novus Bartsch, 2013 (asterisk).