Phthiracarus laevigatus

van der Hammen, L., 1963, The Oribatid Family Phthiracaridae II. Redescription of Phthiracarus laevigatus (C. L. KOCH), Acarologia 5, pp. 704-715 : 704-714

[Redescription of PHTHIRACARUS LAEVIGATUS (C. L. KOCH)]

The present paper deals with Koch's Hoplophora laevigata , characterized by this author as a large species, with a highly arched and shiny notogaster, of which the hairs were invisible to him (so that they are very small), and a short sensillus that is curved to the front; he described the colour as rust-yellow (in the latin diagnosis defined as ferrugineus = rust-coloured or reddish brown; the coloured figure which accompanies the text is indeed rather dark brown), the notogaster presenting a black border, and the aspis the usual pair of light spots; the ano-genital region and the legs are described and figured as lighter. There can be no doubt about the belonging of laevigata to the genus Phthiracarus because of the smooth cuticle and the absence of a distinct median prodorsal carina.

Among the nine species of the genus Phthiracarus collected by me in the surroundings of Regensburg, there is only one of which the notogastral hairs are inconspicuous, all other species having longer notogastral hairs that are much more distinct. This species is, moreover, the largest of all and has a highly arched notogaster, characters that exactly fit in with Koch's description of Hoplophora laevigata , just as the shape of the sensillus and the colour. Consequently, there is sufficient proof for the identity of Koch's original description and the material collected by me. This own material has served me for the present redescription.

Jacot (1936) was the first to re-identify the species on the same grounds. His description is sufficient for an identification, but several characters that are interesting for a future subdivision of the genus Phthiracarus are not mentioned. I point for instance to the number of lyrifissures, and to the number and position of vestiges of hairs. Because Jacot mounted his specimens in balsam, he often could not see the difference between a place of insertion of a hair, a vestige of a hair, and a lyrifissure.

Sellnick (1928, 1960) identified laevigatus with a species of Steganacarus ; it is, however, evident that a species described by Koch as shiny and smooth (the translation of " laevigatus " is moreover, " polished " or " smooth ") cannot belong to Steganacarus , a genus with distinctly sculptured cuticle and a distinct median prodorsal carina.

Phthiracarus laevigatus was characterized by Jacot as the only Regensburg species of which the genital valves present a distinct anterior apophysis. This apophysis has afterwards been observed in other species, and is for instance also present in P. nitens Nicolet. In the surroundings of Regensburg I discovered another species presenting this character, viz., the species above referred to as P. cf. contractilis . I do not know whether Jacot confused the two species. P. cf. contractilis is distinctly different from P. laevigatus by the less arched notogaster, the absence of the characteristic angle near c1, and the longer notogastral hairs. Apparently, it has also a habitat that differs from that of P. laevigatus , because I collected it in the large forests of spruce-fir (Schwaighauser Forst, Donaustaufer Forst), where P. laevigatus has not been found.

Jacot (1930) considered P. contractilis Perty (the type of the genus Phthiracarus ) a synonym of P. laevigatus . Perty's figures of the species, published by Claparède (1868), show, however, a yellowish brown mite, of which the notogaster is much less arched, without the characteristic angle near c1. Because Perty's species was also collected in Bavaria, there is some chance that it is identical with my material from fir-woods. There are, however, still more species of the group in Bavaria, as I collected a third one in München. I hope to return to the important contractilis problem in one of the following papers of the series; a neotype must be designated before the genus Phthiracarus can be subdivided.

The study of P. laevigatus is thwarted by the behaviour of the specimens in lactic acid. Notwithstanding the fact that the species looks rather solid, heating with lactic acid causes serious deformation of the cuticle, whilst gass- and oilbubbles are formed in the interior. The results with slow heating in diluted lactic acid proved to be only little better. Among twenty specimens treated in this way, a few appeared to be completely suited for the preparation of detailed figures. In the present paper those structures which show little differences from Hoplophthiracarus pavidus (cf. van der Hammen, 1963), such as the gnathosoma and the coxisternal region, are not described again. Especially such characters are emphasized here, that will possibly prove to be important for a future subdivision of the genus Phthiracarus .

Phthiracarus laevigatus (C. L. Koch, 1841).

Hoplophora laevigata C. L. Koch, 1841, fasc. 38 (16); 1842, p. 117, pl. 12, fig. 66.

Phthiracarus laevigatus , Jacot, 1936, p. 167, figs. 1-6.

Material. - The topotypic material from the surroundings of Regensburg (Bavaria, Germany) dealt with here, comprises the following specimens (localities arranged from West to East, and from North to South).

Keilstein near Keilberg , June 15, 1961; deciduous forest mixed with pines; litter: 6 specimens (sample 61 R 23). Idem , deciduous forest; litter and moss from stones and stubs: 20 specimens (sample 61 R 24).

Donaustauf , June 27, 1961; hedge of elder along brooklet; decaying wood, leaves, and branches: 21 specimens (sample 61 R 45).

Dechbetten , July 17, 1959; small moist wood, mainly consisting of elder; moss: 3 specimens (sample 59 R 1). Idem , June 18, 1961; small deciduous wood on a slope (Koch's " Feldhölzchen "): 2 specimens (sample 61 R 32).

Königswiesen, June 18, 1961; village-park; litter and moss: 9 specimens (sample 61 R 31).

Hohengebraching , July 20, 1959; forest named " Argle " (spelled by Koch as " Arklee "); mixed forest; moss and litter: 1 specimen (sample 59 R 10). Idem , part of the forest with beech; litter: 2 specimens (sample 59 R 11). Idem , June 17, 1961; small, moist, open part in the forest, with grass and herbs; moss, roots, and decaying grass: 29 specimens (sample 61 R 28).

Total: 93 specimens from 9 samples.

Because the type-material of Koch's Oribatid mites is no more in existence, a female from sample 61 R 45 is designated here as neotype; it is preserved in the collection of the Rijksmuseum van Natuurlijke Historie, Leiden.

Occurrence. - From the above-mentioned data it appears that the species has been found in moss and decaying material (wood, leaves, grass, roots), collected in forests, small woods, and hedges of mainly deciduous trees. The distribution around Regensburg is local; with some additions it still corresponds with the data given by Jacot (1936). The species is apparently absent in the large forests of spruce-fir North of Regensburg (Schwaighauser Forst, Donaustaufer Forst; although in the last-mentioned region it is found in the parts with deciduous trees). The occurrence reasonably corresponds with Koch's description of it: " An Feldrainen in Erdmoos, unter Hecken und Gebüsch, hier ziemlich selten ".

Measurements. - 19 specimens from sample 61 R 45 (Donaustauf) have been measured (2 had been damaged during the observations), of which 6 are males, and 13 females. The measurements in the two sexes are the following:

Male: length of prodorsum 0.345-0.415 mm (average 0.395); length of notogaster0.625-0.760 (average 0.720), height 0.465-0.620 (average 0.550).

Female: length of prodorsum 0.390-0.540 mm (average 0.475); length of notogaster0.705-1.05 (average 0.890), height 0.540-0.870 (average 0.705).

Habitus and colour. - The species is a relatively large Phthiracarus wit ha characteristic shape which sometimes can even be recognized without any magnification at all. The notogaster is highly arched and presents a distinct angle near c1. The surface is very shiny. The notogastral hairs are small and extremely thin. As a rule the specimens are rust-coloured to chestnut-brown. The notogastral limb is much darker, whilst the ano-genital region is lighter except for a dark transverse band; the aspis presents the usual pair of light spots.

Cerotegument. - A cerotegument-layer is nearly absent; some vague granulations can be seen in the lateral part of the notogaster. I observed small white granular masses in the projecting part of the anterior notogastral limb.

Cuticle. - When observed in a dry condition on a carbon block, the cuticle is extremely shiny, and nearly completely smooth. A faint superficial structure is, however, present, although nearly indistinguishable; it seems to be vaguely shagreened, but in fact it is punctate.

The cuticle is very thin and can be easily damaged when preparing a specimen for study. After heating with lactic acid, the mites offen show a distinct swelling, consisting in a partial Separation of epiostracum and ectostracum, a phenomenon of osmotic origin. In these cases the brown ectostracum shows partial fractures, whilst the pale epiostracum is still entire. The epiostracum is distinctly punctate; each small circular area contains a point. The ectostracum shows a structure of fine points.

Prodorsum (fig. 4A). - The prodorsum or aspis presents a distinct lateral ridge, and a pair of anterior light spots which are in fact sunken areas separated by an indistinct median carina The sensillus is represented in fig. 4 C; it consists of a slightly eccentric core and a surrounding border which is pointed towards the apex. The bothridium is crenate with about eight segments; in lateral view the posterior upper part appears to be covered by a fold. The thin interlamellar, lamellar, rostral, and exobothridial hairs are lying rather close to the surface of the aspis. The first-mentioned three pairs of hairs have distinct canals at the place of insertion; especially those of the rostral hairs are strikingly long.

Notogaster (fig. 1). - The notogaster is highly arched. The outline presents a characteristic angle near c1, whilst the part between c1 and the anterior border is steeply sloping (these characters are already mentioned by Jacot, 1936, p. 167). The notogastral hairs are very small and thin; their disposition is represented in fig. 1; f1 and f2 are vestiges, just as in Hoplophthiracarus , f1 being situated still more posteriorly of hv There are four pairs of lyrifissures (instead of two pairs in Hoplophthiracarus pavidus and Phthiracarus anonymum ), indicated here as ia, im, ip, ips; I am not certain as to the notation of the last-mentioned two fissures. The usual mark µ of a muscle is easily visible.

Ano-genital region (figs. 2, 3 A-B). - Although the ano-genital region must be considered a fusion of anal, adanal, genital, and aggenital shields, the covers are simply indicated here as anal and genital valves.

The hairs of the ano-genital region have the number usual for Phthiracaridae : 9 genital hairs (of which those numbered here by 5-9 are small and marginal, especially 5-7), 1 aggenital hair (with an anterior lateral position, its base covered by the overhanging anterior border of the valve), 2 marginal anal hairs, and 3 adanal hairs (of which ad1 and ad2 are vestiges, whilst ad3 is curved backwards). The vestigal condition of two adanal hairs will perhaps prove to be a useful character for the subdivision of the genus Phthiracarus .

The anterior border of the genital valves presents a median apophysis which is especially distinct in lateral view (fig. 3B). The posterior border of the genital valves, and the anterior border of the anal valves present a row of some 6 teeth which constitute a lock.

The anterior median lock of the anal valves is the reverse of the condition in Hoplophthiracarus . In P. laevigatus the left lobe is the external one which fits in a corresponding lock in the right valve; the right lobe is underlying. I name this condition right-fitting, in contradistinction to the condition in Hoplophthiracarus , which consequently must be named left-fitting. Possibly these conditions will prove to be characters of generic value.

I have found no specimens with extended ovipositor. It. is not impossible that only those specimens which drop in alcohol during their search for suitable spots for egg-laying, have the ovipositor extended. The number of genital papillae is apparently 2; vestiges of a third pair could not be established with certainty.

Palp (fig. 4B). - The palp consists of three joints. The formula is 2-2-7. The solenidion omega is free. The tarsus has three distinct eupathidia: acm, ul", and ul'; the last-mentioned eupathidium has a relatively large basal ventral tooth, probably representing the remainder of the subultimal hair su which has joined ul'.

In fig. 4 B a small part of the infracapitulum is also represented, showing the long pectinate supracoxal hair e.

Legs. - Just as in Hoplophthiracarus pavidus (cf. van der Hammen, 1963) the number of hairs on the legs is considerably reduced, so that consequently the correct notation is difficult to establish. In some cases, the hairs are, moreover, not placed in distinct pseudo-symmetric pairs, by which condition the Identification is thwarted. The long solenidions, especially 9, are unfavourable for a correct orientation, and must be cut off if necessary; s and consequently the plane of pseudosymmetry should preferably be orientated exactly horizontally in the slide.

Legs I and IV are completely represented in respectively figs. 5 A-C and 6 A-C '> I have, moreover, added figures of tarsus II (fig. 5 D) and tarsus III (fig. 6 D). In my opinion the notation given in these figures is reasonably certain. The difficulties concern the tarsi, especially of the posterior legs.

Tarsus I has 6 eupathidia: (if), (p), s, and a'. The antelateral pair of hairs (a), which is here regarded as consisting of an eupathidium (a') and an ordinary hair (a"), is not placed pseudosymmetrically: a" has a lateral (antiaxial) position, a' (the eupathidium) is nearly in the plane of pseudosymmetry. A similar orientation of the antelateral hair a" is found in tarsus II; here it is directed even upwards. Tarsus II lacks the iteral hairs (which are also absent 011 tarsi III and IV) and the primiventral hair pv' (unless the hair indicated here as a' will prove to be pv'). The numbers of hairs on tarsi III and IV are still more reduced. The identification of the hairs is here especially difficult because (tc), (p), and (u) are not placed in distinct pairs. There is only one antelateral hair on III and IV, viz., a'. Just as in Hoplophthiracarus pavidus tarsus III has a pair of fastigial hairs (ft) but no primiventral hairs (pv), whilst tarsus IV has one fastigial and one primiventral. The formulae from I to IV are the following.

Hairs: I (1-4-2-5-16-1); II (1-3-2-3-12-1); III (2-2-1-2-10-1); IV (2-1-1-2-10-1).

Solenidions: I (2-1-3); II (1-1-2); III (1-1-0); IV (0-1-0).

The solenidions of the tarsi are free. On all tibiae phi is coupled with d. On genu I sigma2 is coupled with l', whilst sigma1 is free; d is absent.