Axenyllodes ghilarovi ( Martynova, 1964 )

Babenko, Anatoly, Shveenkova, Yulia & Arbea, Javier I., 2025, Two new and two little-known species of the genus Axenyllodes Stach, 1949 from Russia and Kazakhstan, Zootaxa 5583 (1), pp. 154-170 : 155-158

Axenyllodes ghilarovi ( Martynova, 1964)

Basionym: Xenyllodes ghilarovi Martynova, 1964: 61

Figs 1–12

Holotype, female labeled as “ Kursk Region, Central Tsernozemny State Nature Reserve , meadow steppe, 17.X.1957. Yu.B. Byzova leg.”

Additional material. 8 females, Russia (European part), Middle Volga River Basin, Penza Region,“Privolzhskaya Lesostep” State Nature Reserve , meadow steppe with Brachypodium pinnatum , sandy loam chernozems, soil (0–10 cm), 52.4858 o N 46.2113 o E, 22 September 2017 ; 8 females, same biotope, but 01 October 2019; 1 female, same biotope, but 27 September 2018; 4 females, same biotope, but 18 September 2020; 1 female, same area, 52.4860 o N 46.2116 o E, steppe meadow with sparse undergrowth of trees (pine, oak), shrubs (broom) on forest border, 15 September 2022. All Yu. Shveenkova leg.; 5 females, north-western Kazakhstan, Zhanibek Research Station [49.42 o N 46.85 o E], semi-desert, 02 October 2002. V. Beiko leg.

Diagnosis. A species of the genus characterized by the presence of 6 differentiated dorsal sensilla and a rather large microsensillum on Ant. IV; 2+2 large ocelli without traces of dark pigment under them; coarse cuticular granulation with rather small oval fields with finer granules on the head and terga; triangular shape of PAO, sometimes slightly hidden under cuticular fold; the absence of lateral microsensilla and the presence of setae m1 on Th. II–III; the basic generic type of VT, tenaculum and furca; 10–10–9 setae on the tibiotarsi, some of which being clearly longer and 7–7–(6)7 setae on the femora; manubrial field with 7+7 setae and rather large AS set on subequal papillae.

Redescription. Length (without antennae) 0.62–0.74 mm.Habitus typical of the genus:body prolong, appendices short. Colour white without any traces of dark pigment. Tegument granulation coarse, secondary granules rounded at tip. Head, thorax and abdomen with small fields of finer granulations located symmetrically with respect to medial line ( Fig. 1 ).

Antennae about as long as head. Ant. IV with a large simple vesicle apically, six rather thin, but clearly differentiated sensilla with pointed apices (three dorso-external [S7–S9] and three dorso-internal [S1, S2, S4]), ms large and broadened at apex, notably shorter in length than sensilla, subapical organite present ( Fig. 2 ); ventral side of Ant. IV with few ordinary setae ( Fig. 3 ). Antennal organ of Ant. III typical, inner sensilla small, sgv & sgd about twice as long, ms and 16–17 ordinary setae present on Ant. III. Ant. I–II with 7 and 10 setae, respectively.

Head with 2+2 rather large ocelli, their diameter equal to 0.44–0.53 of PAO length, distance between them usually smaller than their diameter (0.7–0.9: 1). PAO triangular in shape, located in a cavity and sometimes slightly hidden under a small cuticular fold ( Fig. 4 ). Buccal cone short, typical of the genus. Labrum with three prelabral and 8 labral setae, medial pair of setae in anterior row stronger, with tips curved laterally. Maxillary palp simple. Labium with five apical spinules and three common setae subequal to them in length. Basomedial and basolateral fields of labium with 4+4 setae, respectively. Maxilla typical of the family with strong, triangular head, mandibles invisible. Ventral side of head with 3+3 postlabial setae along ventral line ( Fig. 5 ).

Ordinary setae on dorsal side of body smooth and acuminate, slightly longer on last abdominal terga, sensilla undifferentiated ( Fig. 1 ). Main characteristics of dorsal chaetotaxy: setae m1 present on Th. II–III and absent from Abd. IV; Th. II–III with three setae present in a-row (a1, a3 and a5), a2 and a4 absent from both terga, m-row with two setae (m1 and m4) and a lateral sensillum in m6 position, and five setae in p-row, lateral microsensilla invisible; a-row on Abd. I–III complete, with five setae (a1, a2, a3, a4 and a5).

Thoracic sterna without setae. Ventral tube with 3+3 distal setae, one seta also present on each side of VT on sternum of Abd. I, Abd. II–III with 4–5 ventral setae on each side ( Fig. 6 ). Tenaculum with 2+2 teeth.

Furca small ( Figs 6–7 , 12 ), manubrium with 4+4 setae on main part, 1+1 basal setae and 2+2 basolateral setae (7+7 altogether); dorsal side of dens with two setae and rather fine granulation. Mucro about as long as dens, strongly hooked, lateral lamella not especially high and poorly visible. Anal spines strong and curved, set on subequal papillae. Anal opening located almost terminally ( Fig. 8 ).

Legs I–III with 1, 2, 2 setae on upper subcoxae, 0, 2, 2 setae on lower subcoxae, 3, 5, 5 setae on coxae, 5, 5, 4 on trochanters, 7, 7, (6)7 setae on femora, and 10–10–9 setae on each tibiotarsi, the latter setae clearly differing in length. Unguis toothless, unguiculus tiny, needle-shaped ( Fig. 9 ).

Remarks. The only known type specimen, which the original description was based on, has only one anal spine at the end of the abdomen ( Fig. 11 ) and one additional seta (a4) on Th. III ( Fig. 10 ). The presence of the latter seta was also sometimes observed in our material, but rather rarely and usually asymmetrically. Otherwise, the holotype fully corresponds to the above description.

In 1964, when the original description of A. ghilarovi appeared, only two species were known, which currently considered representing the genus Axenyllodes : A. bayeri and A. caecus . Of these, only the former one has, like A. ghilarovi , 2+2 ocelli, and naturally Martynova compared her new species to this very species. These two species are easily distinguished by the shape of the PAO—four-lobed in A. bayeri and triangular in A. ghilarovi . There are also a number of other morphological differences presented in Table 1 .

However, at least six species of the genus are presently known that, like both A. bayeri and A. ghilarovi , are characterized by the presence of 2+2 ocelli: A. minitaurus ( Ellis, 1976) , A. microphthalmus Fjellberg, 1995 , A. marci Thibaud & Peja, 1996 , A. ukrainus , A. sinensis Tamura in Tamura & Yue, 1999, and A. britannicus Thibaud, 2006 ( Table 1 ). Of these, four species, A. minitaurus , A. microphthalmus , A. ukrainus , and A. britannicus , are characterized by the presence of anal spines and the most complete number of tibiotarsal setae in the genus, while A. marci lacks anal spines, whereas A. sinensis has only 7 setae on each tibiotarsus.

Axenyllodes microphthalmus , described from the Canary Islands, differs primarily by the very small size and the position of the ocelli: ocelli separated by 3–4 times their own diameter ( Fjellberg 1995, p. 153), whereas this distance is subequal in A. ghilarovi . Axenyllodes minitaurus (Crete) can easily be distinguished from A. ghilarovi by the location of the PAO: in the former species it is sunken below the integument in a cavity communicating with the surface via a triangular fissure ( Ellis 1976, p. 255), while in the latter it is only sometimes partially hidden on one side under a small cuticular fold. Besides this, A. minitaurus appears to have less setae on the manubrial field: 5+5, vs 7+ 7 in A. ghilarovi . Axenyllodes britannicus is also fairly easily distinguished from A. ghilarovi , since it is characterized, according to the original description, by the presence of lateral microsensilla and the absence of setae m1 on the thoracic segments.

It appears especially difficult to distinguish A. ghilarovi from A. ukrainus , primarily due to the relatively incomplete description of the latter species.The known morphological differences between these species are confined to the shape of the PAO (three-lobed in A. ukrainus , vs broadly triangular in A. ghilarovi ) and the number of setae on the manubrial field: A. ukrainus is said to have 3+3 basolateral setae as in Fig. 13 , while A. ghilarovi always has only two setae in this position ( Fig. 6–7 , 12 ). There are also some minor differences in the fine structure of the antennal organ. In A. ghilarovi , sgv & sgd are clearly longer than inner sensilla of Ant. III, whereas A. ukrainus , according to the fig. 1 in Thibaud & Taraschuk (1997), has subequal sensilla and ms in Ant. III. The two species are probably also distinct ecologically: although they were described from adjacent areas, the type specimens of A. ukrainus were collected on a sandy beach of the Black Sea, while A. ghilarovi clearly prefers rather rich steppe areas.

Below one more species with 2+2 ocelli, A. chinki sp. nov., is described. Axenyllodes ghilarovi can hardly be compared to it, since it has no anal spines and only 7–7–7 tibiotarsal setae (see also Table 1 ).

Figures

FIGURES 1–9. Axenyllodes ghilarovi: 1, cuticular granulation and dorsal chaetotaxy; 2, antenna, dorsal view; 3, ibid., ventral view; 4, PAO and ocelli; 5, head, ventrolateral side; 6, ventral chaetotaxy of abdomen; 7, furca; 8, anal lobes; 9, tibiotarsus I. Scales: 1, 5–6, 0.1 mm, 2–3, 7–8, 0.05 mm, 4, 9–0.01 mm.

FIGURES 10–15. Axenyllodes ghilarovi (10–12), A. bayeri (13), A. nematodes (14) and A. echinatus (15): 10, dorsal chaetotaxy of head and thorax, holotype; 11, abdominal tip, holotype; 12–15, chaetotaxy of manubrial field: m—setae on main part, b— basal setae and bl—basolateral setae. Scales: 10–11, 0.1 mm, 12–15, 0.01 mm.