Hoplophthiracarus pavidus

van der Hammen, L., 1963, The Oribatid Family Phthiracaridae I. Introduction and Redescription of Hoplophthiracarus pavidus (Berlese), Acarologia 5, pp. 306-317 : 307-317

Hoplophthiracarus pavidus (Berlese, 1913).

Material. - 394 adult specimens from a sample of Sphagnum, collected on August 9, 1962 in the Vegetation around a fen near Wijster (province of Drente, Netherlands) .

The sample contained no other species of Phthiracaroid mites. Larvae and nymphs were not found, but they will certainly prove to occur inside the stems of the mosses. Most of the adult females contain praelarvae. Males are not present among the material, so that parthenogenesis is probable.

Measurements. - Length of prodorsum 0.180-0.225 mm (average 0.200); length of notogaster 0.295-0.395 (average 0.360), height 0.220-0.395 (average 0.250), broadth 0.250-0.295 mm (average 0.270).

Habitus and colour. - The species is at once recognizable by the strikingly curved notogastral hairs and the nearly erect interlamellar hairs.

The colour of the notogaster is rather dark chestnut brown; the anterior and ventral limbus is still darker. The anterior border of the genital plates and the border between genital and anal plates are also darker. The prodorsum or aspis is lighter brown, with a posterior median and two anterior lateral dark spots. The legs are light brown. All hairs are whitish.

Cerotegument. - The cerotegument layer is best visible in old specimens, when these are studied in transparent light. It appears then to consist of irregular masses of granules which are connected with each other in a whimsical way. The layer is especially distinct in the lateral regions of the notogaster.

Cuticle. - The cuticle is shining. The surface is mainly shagreened as in Phthiracarus , but the anterior limbus and the anterior ventral part of the notogaster close to the ventral limbus (not the ventral limbus itself) have a punctate structure as in Steganacarus . These punctate areas are easily discernable when the animal is studied on a carbon block, in reflected light.

Prodorsum. - A lateral view of the prodorsum or aspis is given in fig. 1, a dorsal view in fig. 2 A. In both views the lateral ridge is distinct; there is no dorsal ridge.

The three air-sacs attached to the bothridium are easily visible (fig. 3 B). The sensillus is directed sideward; it has a thickened distal part with blunt tip. The bothridium presents the usual scale.

Apart from the sensillus there are 4 pairs of prodorsal hairs: interlamellar, lamellar, rostral, and exobothridial hairs. The interlamellar hairs are erect, slightly curved backward in the distal part. The small lamellar hairs are close to the bothridium. The rostral hairs are directed to the front; from their base a long canal runs through the cuticle.

Notogaster. - A lateral view is given in fig. i, a dorsal in fig. 2 A, and a ventral in fig. 2 B. The limbus is darker than the remaining part of the notogaster. As mentioned above the surf ace of the notogaster is mainly shagreened, but the anterior limbus and the anterior ventral part of the notogaster close to the ventral limbus are punctate. There are 15 pairs of notogastral hairs and 2 pairs of vestiges. In accordance with Grandjean (1950, p. 73, fig. 1) the hairs are indicated with c1 c2, c3, cp, d1, d2, e1, e2, h1, h2, h3, ps1, ps2, ps3, ps4. The vestiges (indicated with f1 and f2) are easily recognizable; one of them (f1) together with the hair h1 is represented in fig. 3 A. I remark that h1 is situated slightly in front of f1 whilst it is behind it in P. anonymum (cf. Grandjean, l. c). The notogastral hairs are rather strong and slightly rough; they are distinctly standing off and curved, mostly to the front.

There are 2 pairs of lyrifissures, viz., ia and im, which are rounded; ia is larger than im. At both sides the usual mark t of a muscle is visible; this muscle runs in. antero-ventral direction to the central part of the hysterosoma.

Ano-genital region (fig. 2 B). - There are 2 pairs of anal hairs, inserted at the inner border. On each cover the 3 adanal hairs are in a distinct row; ad1 is close to the border. The anal covers have a remarkable lock (fig. 3 C, D); in the anterior part it consists of two lobes of which the right one is above the left when the anal opening is closed; the posterior lock consists of some three small lobes at each side, corresponding with small opposite cavities.

There are 9 pairs of genital hairs, of which the anterior 5 are smaller. The last-mentioned hairs are inserted on the inner border of the cover; they have a long canal that runs through the cuticle. The aggenital hair is small; it is difhcult to distinguish because it is inserted in an anterior lateral slit of the cover; it is represented in fig. 1.

The ovipositor (fig. 4) is short and relatively broad. There are a ventral lobe with two pairs of hairs (psi1, and psi2) and two latero-dorsal lobes with each two hairs (tau1, and tau2). The surface of the ovipositor is finely striate, with the exception of the lobes and the distal border. There are only two pairs of genital papulae.

Coxisternal region (fig. 6A). - The epimeral plates are distinctly scleritized, whilst the sternal and sejugal region is weak. The number of hairs on the epimeres is to be expressed by the formula 1 - 0 - 1 - 1. The hairs are strikingly long.

Gnathosoma. - The infracapitulum belongs to the stenarthry type with atelebasic expansion (fig. 5 A); the usual infracapitular hairs h, m, and a are present. There are 3 pairs of adoral hairs (or1-3) on the lateral lips, of which or1 is distinctly pectinate. The dorsal surface of the infracapitulum (fig. 5 B) is partly well scleritized; the labrum and the commissures of the mouth are easily visible. The supracoxal hair e is long and pectinate. In a lateral view (fig. 5 C) the ventral surface of the labrum appears to be undulate.

The chelicerae (fig. 5 D, E) are relatively very large; they have a lateral (antiaxial) and a dorsal hair. Tarsus and apotela each have three dents.

In transparent light, part of the alimentary canal is easily visible. Pharynx, oesophagus, and part of the stomach are represented in fig. 6B. The oesophagus is longitudinally striate. The stomach has an anterior lobe which overlaps the posterior part of the oesophagus. In most of my specimens the stomach contains globular masses of food, in which Sphagnum fragments are possibly present (fig. 6 D).

Palp (fig. 6C). - The palp consists of 4 joints; a trochanter is present. The formula is 0-2-2-7. There is 1 solenidion; acm, ul', and ul" are eupathidia. The subultimal hair sul is completely absent, and there is also no small denticle at the base of ul'. Instead of a pair of ventral hairs, there is only a single hair v. The tarsus of the palp reminds that of Perlohmannia .

Legs. - The number of hairs on the legs is reduced, especially on III and IV. The lyrifissure on leg IV is very small. Genu I has a distinct pore; it is best visible in a dorsal view. Leg I is represented in fig. 7 A, leg IV in fig. 7 B.

The formulae from I to IV are the following:

Hairs: I (1 - 4 - 2 - 4 - 15 - 1); II (1 - 3 - 2 - 3 - 14 - 1); III (2 - 2 - 1 - 3 - 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 claw has a distinct ventral tooth, and an indistinct basal knob.

The notation of the hairs on leg I and IV is given in the figure. There are difficulties as to the tarsus of leg III and IV. It appears that ft' is still present on tarsus III, but that there are only 4 ventral hairs, viz., (u), s, and an antiaxial hair that is either a or pv'. On leg IV the fastigial hair ft' is absent, but there are 5 ventral hairs, viz., (u), s, and a ventral pair (indicated on fig. 7 B, by v' and v") that possibly consists of pv" and a. These problems, caused by the reduction of the number of antelateral (a) and primiventral (pv) hairs, can, however, only be solved in a satisfactory way after comparison of several species of Phthiracaridae and their ontogenesis.

The iteral hairs (it) are absent on III and IV. On tarsus I, the following hairs are eupathidia: (it), (p), and s. The famulus is rather large; it has a characteristic shape that is represented in fig. 7 A.

On genu I, the solenidion sigma1 is coupled with l'; d is no more present, and sigma1 is free. The solenidion phi of tibia I is coupled with d. The solenidions of the tarsus are free.

Praelarva. - The females of Hoplophthiracarus pavidus generally contain praelarvae just as in the two other species of Phthiracaroid mites of which this calyptostase is known ( Phthiracarus anonymum , Oribotritia berlesei ; cf. Grandjean, 1940, 1962). Apparently the praelarva develops rapidly, because I have found no eggs. The number of praelarvae inside the female hysterosoma varies in my specimens from 0 to 4.

The praelarva is very clear and only faintly coloured. The superficial structure of the tegument is partly indistinct; it consists of small folds and faint ridges. Claparede's organ (Cl) is easily visible. In a ventral view (fig. 8 A) vestiges of chelicerae(Ch), palps (Pp), and first pair of legs (PI) appear to be present, separated by faint ridges or folds and by an indistinct superficial sternal ridge; in a lateral view (fig. 8 B) these vestiges look like lobes.