Trachygamasus Berlese, 1903

Witaliński, Wojciech, 2017, A new species of Trachygamasus from Poland, a new definition of the genus, and a key to the world species (Parasitiformes: Parasitidae), Zootaxa 4303 (3), pp. 407-416 : 413-414

Genus Trachygamasus Berlese, 1903

Trachygamasus Berlese, 1903, 1906

Type species. Gamasus pusillus Berlese, 1892 Saprogamasus Willmann, 1949 . Karg, 1971: 420. Type species. Saprogamasus ambulacralis Willmann, 1949 Willmanniella GötZ, 1969. Hyatt, 1980: 320.

Type species. Willmanniella fallax GötZ, 1969

Diagnosis. Deutonymph with separate podonotal and opisthonotal shields, female either with separate shields or with holodorsal shield showing incomplete, short transverse suture in central region of dorsum. Dorsal shield of male complete, with transverse suture, in some cases short. Setae z5 of dorsal hexagon differing in length and form from setae j5 and j6. Gnathotectum in both sexes of trispinate, lateral prongs acuminate, pointed or obtuse apically, central prong either widened distally and bifid/trifid apically, or acuminate. Male chelicerae symmetrical. Corniculi in both sexes conical and rather short. Hypostomatics in male on slightly ventrally elevated cuticle. Seta al of palp femur spatulate or bifid (in T. macfarlanei Costa ), setae al1 and al2 of palp genu spatulate. Tritosternum of female and deutonymph normal, biramous; absent in male. Metasternal shields (paragynia) in female either fused to sternal shield or separated, in part or completely, by a transverse suture; if suture (or groove) is slightly oblique, it is weakly visible and discernible only in axial area of venter. Female genital shield (epigynium) subtriangular. Opisthogastric shield of adults with no more than seven pairs of setae, of which ZV1 is fine. Legs of female and deutonymph without spurs; leg II of male without spurs or with minute spurs. In deutonymphs and adults ambulacra of legs II–IV with acuminate lateral lobes of pulvilli.

Remarks. The genus Trachygamasus was introduced by Berlese in 1903 as a subgenus, but diagnosed by Berlese (1906) as showing several distinct characters. These include a thick and pseudoperforated cuticle (i.e. showing many pits), ambulacra with acuminate pulvilli, and an unarmed second pair of legs in males. Costa (1962) proposed that a two-segmented ambulacrum of leg I is a characteristic feature, but this feature is typical for Parasitidae , in which the ambulacrum of leg I possesses a praetarsus. Micherdziński (1969) noted for Saprogamasus (= Trachygamasus ) ambulacralis Willmann that ambulacral pulvilli (his lobi membranosi) are fourpartite, one pair (anterior) is terminally rounded whereas the second (lateral) pair is narrow and acuminate. A further diagnosis by Hyatt (1980) focused on (1) the shape of lateral pulvilli of ambulacra II–IV which are acuminate, (2) the relation of the sternal shield to paragynia in the female, (3) the absence of spurs on leg II in the male, and (4) the absence of a tritosternum in the male.

In Parasitidae females, the anterior margins of the paragynia form oblique sutures with the posterior sternal margin. In Trachygamasus , characteristic traits include the transverse orientation of these sutures (e.g. T. ambulacralis , T. gracilis ) or fusion of sternum and paragynia resulting in no sutures at all (e.g. T. macfarlanei , T. medianus , T. pusillus ). However, Karg (1998) showed slightly obliquely oriented sutures in T. biplumatus . In T. gerdi sp. nov., the paragynia are fused with the sternum, and sutures are absent; instead, near the axis of the venter two short, oblique grooves marking the border between the fused paragynia and sternum are discernible.

In Trachygamasus males, the most conspicuous feature is the absence of spurs on leg II ( Berlese, 1906; Hyatt, 1980). However, in three species, T. borealis Ma & Wang , T. medianus Tichomirov and T. gerdi sp. nov., minute spurs on femur, genu and tibia of leg II are present.

Another characteristic feature present in all Trachygamasus species is the absence of a tritosternum in males, whereas in females the tritosternum is well pronounced and biramous ( Hyatt, 1980).

The male genital opening in at least three species ( T. ambulacralis (Willmann) , T. medianus Tichomirov and T. gerdi sp. nov.) consists of a conspicuous genital lamina with a characteristic hyaline uniramous protrusion, long but poorly visible ( Tichomirov, 1977: p. 96, fig. 41/4; Hyatt, 1980: p. 364, fig. 63/G; this study: fig. 17).