Lobohalacarus weberi ( Romijn & Viets, 1924 )

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 : 85-88

Lobohalacarus weberi ( Romijn & Viets, 1924)

Walterella weberi Romijn & Viets, 1924: 217–220 , figs 3–6.

Lobohalacarus weberi, Schwoerbel 1955: 147 , fig. 1; Green and MacQuitty 1987: 162, fig. 68A–D; Bartsch 2006: 128–130, fig. 5-8a–f, 2007: 74–80, fig. 2, 2011: 493–494, fig. 3A–C.

Walterella weberi quadripora Walter, 1947: 236–237 , fig. 35.

Lobohalacarus weberi quadriporus, Viets 1959 : pl. 4, fig. 42, pl. 5, fig. 47.

Lobohalacarus weberi gotoensis Imamura, 1970: 455– 457 , figs 1 and 2.

Lobohalacarus weberi tristanensis Bartsch, 1995: 171– 175 , figs 1–13.

Species with vague descriptions but expected to belong to L. weberi :

Halacarus processifer Walter, 1919a: 21–23 , fig. 1–3 (only protonymph known);

Lobohalacarus hummelincki Viets, 1940: 191–194 , fig, 1,2I and II, 3III and IV, 4;

Lobohalacarus bucharensis Jankovskaja, 1967: 109– 114 , fig. 1(1–7), 2(1–7), 3(1–6) (only deuto- and protonymph known);

Lobohalacarus bunurong Harvey, 1988: 363–365 , figs 1–6.

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 , small stream crossing the railroad east of village, 200 m, 15 Aug. 2001 ( MD027 ) . – 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, 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 ) . – Northern Madagascar, Antsiranana, Andapa , right affluent of River Amben- drana downstream, large cascade, 600 m, 11 Nov. 2001 ( MD147 ) .

Short description ( Fig. 4A–E ). Female: Length (with frontal spine included) 249–304 [25] µm, 228–273 (if frontal spine excluded). All Madagascar specimens with frontal spine, spine generally slender ( Fig. 4C ) and about 21–31 µm long, one female with 19 µm-long spine. Dorsal plates uniformly foveate, foveae 3 µm wide. AD and anterodorsal part of AE fused ( Fig. 4A ). Opposing edges of AD and PD truncate. OC oblong, without cornea or eye pigment. Dorsal setae minute, seven pairs present, most posterior pair on PD. Ventral plates AE, PE and GA fused to a shield ( Fig. 4B ). A pair of epimeral pores about levelling with aperture of legs II. GO extending anteriad to the level of apertures of legs IV. Area corresponding to PE with one rather short dorsal and two long ventral setae, genital area with four to five pairs of setae. Each genital sclerite with two to three gac. Gnathosoma slen- der, 1.8 times longer than wide. Rostrum almost extending to end of P-2 ( Fig. 4D ). P-2 with single dorsal seta, P-3 with medial spur. Length ratio leg I:idiosoma 0.8:1, following legs somewhat shorter. Telofemur and genu I equal in length ( Fig. 4E ). Telofemora III and IV with 2/0 dorsal/ventral setae. Genu I with two ventral setae, generally one seta spur-, the other seta-like, rarely both setae spur-like. Tibia I ventrally with two pairs of setae, one pair spiniform, one bristle-like; ventral flank of tibiae II to IV with (zero to) one smooth and (one to) two pectinate setae. Tarsus I with ventromedial spur, apically with pair of eupathidia (short sensory setae) and pair of doubled pas ( Fig. 4E ); tarsus III with 4/1 dorsal/ventral setae, and tarsus IV with 3/1 setae. Lateral fossa membrane of tarsus I enlarged, its length 7 µm, height 6 µm, on following tarsi lateral and medial fossa membrane small both in length and height. Claws on tarsus I smaller than those of following tarsi.

To get an idea of variants in respect to external characters, as commonly found in Lobohalacarus weberi ( Bartsch 1995, 2007, 2011), details of 25 uncleared females were examined in a drop of glycerine, but some females were damaged or the characters in question obscured. The character studied were (1) frontal spine: present [25]; (2) number of gac per genital sclerite: 2 [12], 3 [38]; (3) number of pgs in each half of genital plate: 3 [1], 4 [22], 5 [26]; (4) combination of spines (sp) and bristles (br) on genu I: sp / br [49], sp / sp [1]; (5) number of dorsal / ventral setae on telofemur III: 2 / 0 [47], 2 / 1 [1]; (6) number of dorsal / ventral setae on telofemur IV: 2 / 0 [49], 2/1 [0]; (7) number of pectinate (p) + smooth (s) setae on tibia II: 2p+1s [46], 1p+1s [4]; (8) number of pectinate (p) + smooth (s) setae on tibia III: 2p+1s [31], 1p+1s [14]; (9) number of pectinate (p) + smooth (s) setae on tibia IV: 2p+1s [48], 1p+1s [0]; (10) number of dorsal / ventral setae on tarsus III: 4 / 1 [43], 4 / 0 [1], 3 / 0 [0]; (11) number of dorsal / ventral setae on tarsus IV: 4 / 1 [1], 3 / 1 [45], 3 / 0[2].

Male: Not present.

Juveniles: Length (frontal spine excluded) of deutonymphs 230–247 [3] µm, protonymphs 210 [2] µm and larvae 130–162 [4] µm. All instars with slender frontal spine, in one larva that spine very delicate. Ventral plates AE, PE and GA separated. Tarsus I with three dorsal setae, dorsolateral solenidion, enlarged lateral fossa membrane, ventromedial spur, and two ventral eupathidia.

Biology. Eighteen of 26 females enclosed an egg, one female two eggs. The smallest egg was globular and had a size of 40 x 40 µm, the largest one reached a size of 110 x 56 µm.

No male was found in the material from Madagascar. Though L. weberi is one of the very wide-spread and commonly recorded species reliable records of males are lacking.

Remarks. Two easily recognized characters used for identification of Lobohalacarus weberi are the frontal spine and the ventral shield. These characters are known to vary, though rarely. In the samples from Madagascar, all individuals have a pointed frontal spine and a ventral shield. In almost all Madagascan specimens the frontal spine is very slender, similar to that illustrated by Schwoerbel (1955: fig. 1(4)). In general, the spine is somewhat shorter but wider (cf. Romijn & Viets 1924: figs 3 and 4; Bartsch 2006: fig. 5–8a and b). Among ma- terial from Inaccessible Island, Tristan da Cunha Islands, three out of six females had no frontal spine. In two of these three specimens the anterior margin of the idiosoma was evenly arched, in one the spine was reduced to a hood-like process ( Bartsch 1995: figs 12 and 13). Out of 92 individuals from New Zealand, one female had no spine but an evenly rounded anterior margin, 91 females had a frontal spine ( Bartsch 2007: fig. 2A–C). In the same material one of the females had no ventral shield, instead AE, PE and GA were separated ( Bartsch 2007: fig. 2C). Lobohalacarus weberi is expected to be highly variable in its morphology rather than to be represent- ed by several cryptic species. Studies on the influence of habitat parameters on character expression do not exist.

Geographical distribution of Lobohalacarus weberi

and the Lobohalacarus weberi complex ( Fig. 5 ) (cf.

Bartsch 2008a, b, 2011, 2014a; Pešić et al. 2010; Fritz &

Feminella 2011; Stolbov et al. 2018):

Afrotropical Region. – Kenya – Madagascar – Tristan da Cunha Islands;

Palaearctic Region. Europe: – Austria – Belgium – Unit- ed Kingdom ( England, Northern Ireland, Scotland) – Bulgaria – Denmark – Faeroerne – Finland – France – Germany – Greece – Hungary – Iceland – Italy – Macedonia – Monte Negro – Poland – Portugal – Romania – Switzerland – Spain – Sweden – The Netherlands. Northern Africa: – Tunisia. Asia: – Iran – Japan ( L. weberi gotoensis — Imamura 1970) – Russia (Tyumen region) – Uzbekistan ( Lobohalacarus bucharensis — Jankovskaja 1967);

Nearctic Region. – Canada (British Columbia, New Brunswick, Newfoundland, Ontario, Quebec). – Unit- ed States (Alabama, Arizona, California, Colorado, Georgia, Illinois, New Hampshire, New Mexico, New York, North Carolina, Rhode Island , Tennessee, Virginia) ;

Neotropical Region. – Chile (Magallanes) – Peru (Lake Levandera, Lobohalacarus processifer ) – Venezuela (near Higuerote, Lobohalacarus hummelincki );

Australian Region. – Australia (New South Wales ( Lobohalacarus sp. ), Queensland, Victoria ( Lobohalacarus bunurong and Lobohalacarus sp. ), the author expects these specimens to belong to the L. weberi complex). – New Zealand (North and South Island);

Pacific Islands. – Hawaiian Islands.

Figures

Fig. 4A–E. Lobohalacarus weberi (Romijn and Viets, 1924), female. A. idiosoma, dorsal; B. idiosoma, ventral; C. frontal spine; D. gnathosoma, ventral;E. leg I, medial. (A, B, D, E, scale = 50 µm; C, scale = 10 µm) (ascl, anal sclerite; ep, epimeral pore; eu, eupathid setae; fsp, frontal spine; pas, parambulacral setae; I-1 to I-6, trochanter, basifemur, telofemur, genu, tibia, and tarsus of leg I).

Fig. 5. Records of Lobohalacarus weberi (Romijn & Viets, 1924) and species of the L. weberi complex.