Ixodes myrmecobii Roberts, 1962

Kwak, Mackenzie L., Ash, Amanda & Elliot, Aileen, 2017, Redescription of the numbat tick Ixodes (Sternalixodes) myrmecobii Roberts, 1962 (Acari: Ixodidae) with descriptions of the male and nymph, and new host records, Zootaxa 4272 (1) : -

Ixodes myrmecobii Roberts, 1962

Ixodes myrmecobii Roberts, 1962: 42 .

Material Examined. Holotype –Female (partially engorged), 19-v-1956, Dryandra, Western Australia, collected by J. H. Calaby. Ex: Myrmecobius fasciatus fasciatus . Deposited in ANIC, CSIRO, Canberra , Australia. Other material examined as in Table 1.

Female redescription. Idiosoma ( Figs 1, 2 , 12, 13 ) Length 3.52–3.70 mm (3.62); width 2.19–2.47 mm (2.30) (unfed). Ovoid; widest at posterior end of scutum. Dorsal and ventral surface with moderate number of fine setae. Marginal grooves well defined. Sternal plate absent. Scutum longer than wide ( Fig 5 ), length 2.13–2.29 mm (2.20), width 1.9–2.25 mm (2.09), widest posterior to mid-length; subtle emarginations present at posterior margin. Cervical grooves present; short. posterolateral carinae present; extending to posterior edge of scutum. Sparse subspiniform setae present. Punctation present; concentrated at anterior end of scutum and on lateral edges.

Scapulae blunt. Genital aperture ( Figs 2 , 13 ) parallel with anterior margin of coxae 4. Genital groove ( Fig. 2 , 13 ) encircling genital aperture anteriorly; curved and separated posteriorly. Anal groove ( Fig. 2 , 13 ) horse-shoe shaped; encircling anus anteriorly; forming a point posteriorly. Spiracular plate ( Fig. 7 ) subcircular with chain of aeropyles along edge of plate; roughly parallel to sides. Length 0.37–0.47 mm (0.41), width 0.27–0.37 mm (0.32). Other aeropyles distributed randomly towards centre of plate. No aeropyles directly around perimeter of loosely crescent shaped spiracle.

Gnathosoma: Dorsal basis capituli ( Figs 3, 4 ) length 1.0 – 1.16 mm (1.08); width 0.65–0.70 mm (0.67). Dorsal basis capituli subpentagonal; posterior margin sinuous; medium sized subcircular porose areas present; separated by more than half their width. Subtle lateral carinae present. Median depression present. Blunt cornua present. Basis capituli subhexagonal ventrally. Blunt auriculae present; directed posteriorly; faint lateral carinae extending from inner margin of auriculae anteriorly. Palps long and slender. Palpal article 1 rounded; three setae present on posterolateral edge; fissure with articles 2 and 3 forming a single curve without irregularity. Articles 2 and 3 fused; suture absent; setae of varying sizes present along length. Palpal article 4 circular and reduced; on ventral side of palpal articles 2 and 3; setae present. Hypostome ( Fig. 4 ) length 0.66–0.90 mm (0.74); width 0.24–0.28 mm (0.27).

Hypostome lanceolate; widest at midpoint; tapered to blunt point. Dentition 3/3; 2/2 posteriorly. Lateral and medial rows with large denticles; inner dental row with small denticles; all dental rows extending to base of hypostome.

Legs ( Figs 6, 8–11 ): Coxa 1 with long blunt external spur. Coxae 2, 3, and 4 with smaller blunt external spurs. All trochanters with small blunt spurs. Syncoxae absent. Tarsi sharply tapering. Tarsus I length 0.12–0.95 mm (0.35). Tarsus IV length 0.12–0.80 mm (0.32).

Male description. Idiosoma: ( Figs 14, 15 , 24, 25 ) Length 2.41–3.72 mm (3.15), width 1.47–2.17 mm (1.92). Ovoid, longer than wide, widest between spiracular plates, marginal body fold narrow but well defined, dorsal setae sparse (<40 µm). Scutum ( Fig. 14 , 24 ) ovoid, convex, punctations fine numerous, setae few and short (<30 µm). Scutum length 2.12–3.53 mm (2.94), width 1.07–1.94 mm (1.61), cervical grooves short and shallow, scapulae bluntly pointed, lateral grooves present, carinae absent.

Ventral plates: ( Figs 15 , 25 ) Pregenital plate subhexagonal, wider than long, length 0.25–0.47 mm (0.37), width 0.20–0.36 mm (0.27), setae (<30µm). Median plate length 1.08–1.82 mm (1.48), width 0.73– 0.07 mm (0.92), extends from coxae III, widening posteriorly with six distinct margins and highly variable dimensions, setae (<40 µm). Anal plate length 0.53–0.81 mm (0.71), width 0.34–0.58 mm (0.47), anterior edge straight and meets median plate anteriorly, lateral margins curving inward meeting in a point posteriorly. Adanal plate with external margin almost straight, running down to body margin, following line of body to anal plate, setae (<55 µm). Ventral punctations mostly fine, scattered but increasing in size around coxae IV and genital aperture, setae scattered and variable in length. Genital aperture parallel with anterior margin of coxae III. Spiracular plate ( Fig. 18 ) ovoid, length 0.28–0.45 mm (0.40), width 0.14–0.28 mm (0.23), a complete chain of aeropyles around plate edge with further incomplete rows distributed toward centre, macula almost central.

Gnathosoma: ( Figs 16 & 17 ) dorsal basis capituli length 0.27–0.47 mm (0.37), width 0.33–0.46 mm (0.38). In dorsal view basis capituli subhexagonal, scattered punctations, cornua absent, posterior margin straight. Ventral basis capituli subpentagonal, palpal article 1 trapezoidal, palpal articles 2 and 3 fused, ovoid dorsally, setae present along inner margin, short setae present on dorsal surface and external edge. Palpal article 4 circular and reduced present on ventral surface of apical end of article 2 and 3, setae present on surface. Hypostome short and broad, length 0.14–0.32 mm (22), width 0.11–0.17 mm (0.14). Hypostome denticles short, rounded, increasing in size mid hypostome, crenulations present on lateral edges, dentition 2/2 of 6 rows.

Legs: ( Figs 19–23 ) Long with pale articulations. All coxae with a blunt external spur and a row of long setae above posterior margin (<175 µm). Trochanters with a small subtle spur. Length of tarsus I is 0.10–0.90 mm (0.45) with moderately long setae (<60 µm). Length of tarsus IV 0.10–0.90 mm (0.44).

Nymph description. Idiosoma: ( Figs 26, 27 , 36, 37 ) Length 1.05–1.40 mm (1.19),width 0.63–1.00 mm (0.80). Fed specimens length 1.50–3.80 mm, width 1.00– 2.60 mm. Unfed specimens ovoid, widest at posterior margin of scutum, with well-defined marginal grooves. Dorsal setae and punctations moderate in number, setae length 50–62.5 µm. Ventral punctations moderate to large, setae shorter than dorsal, length 17.5–47.5 µm, smaller setae situated anteriorly, longer setae laterally and posteriorly. Scutum approximately as long as wide, widest posterior to mid length, posterior angle broadly rounded, lateral carinae well developed and attaining scutum margin. Scutum ( Fig. 31 ) length 0.43–0.72 mm (0.61), width 0.47–0.65 mm (0.57), punctations few and shallow, evenly scattered, setae length 20–25 µm, cervical grooves short and shallow, scapulae blunt. Sternal plate oval with inconspicuous edges, two pair of setae present, length 0.25–0.34 mm (0.30),width 0.07–0.14 mm (0.10) approximately 3 times as long as wide. Spiracles subcircular; length 0.08–0.14 mm (0.12), width 0.06– 0.10 mm (0.08). A chain of aeropyles runs along edge of plate roughly parallel to sides, other aeropyles distributed randomly towards plate centre. Anal groove horseshoe shaped, rounded anteriorly, curving in laterally but remaining open posteriorly.

Gnathosoma: ( Figs 29 & 30 ) dorsal basis capituli length 0.30–0.40 mm (0.27), width 0.17–0.22 mm (0.20). Basis capituli dorsally subtriangular and glabrous, basis ventrally rounded posteriorly with small blunt auriculae. Palps long and slender, palpal article 1 rounded, articles 2 and 3 fused. Hypostome length 0.25–0.30 mm (27), width 0.07 mm (0.07), lanceolate bluntly pointed, widest at mid-point, with sharply pointed denticles, dentition 2/2 of approximately 12 rows.

Legs: ( Figs 28 , 32–35 ) Moderate in length, strong, with pale articulations. Coxae I and II with bluntly pointed external spur, coxae III and IV unarmed, all coxae with syncoxae and a row of setae near posterior margin, trochanters simple. Length of tarsus I 0.04–0.32 mm (0.24) with few long (<50 µm) and some minute setae (<13 µm). Length of tarsus IV 0.04–0.31 mm (0.23).

Differential diagnosis. Female: The female of I. myrmecobii can readily be identified as a member of the subgenus Sternalixodes by the presence of long palps in which articles 2 and 3 are fused as well as an anal groove which meets posteriorly. The absence of a sternal plate serves to distinguish the female of I. myrmecobii from all other sternalixodid ticks except I. holocyclus and I. cornuatus . Ixodes myrmecobii can be distinguished from I. holocyclus and I. cornuatus by a combination of the prominent cornua and rounded, ventrally directed auriculae. In I. holocyclus the cornua are extremely small or absent and the auriculae are ventrally directed while in I. cornuatus the auriculae are angular and incompletely ventrally directed.

Male: Males of the subgenus Sternalixodes are morphologically similar and often difficult to distinguish. Male I. myrmecobii can be distinguished from I. holocyclus and I. cornuatus by presence of an indistinct rounded spur on trochanter III which is sharply pointed and distinct in both I. holocyclus and I. cornuatus . Male I. holocyclus can be distinguished from I. cornuatus by the absence of a spur of trochanter II which is present in I. cornuatus . These diagnostic differences are highlighted in Figures 38–40 .

Nymph: The nymph of I. myrmecobii can be distinguished from all other species of Ixodes by the combination of a sternal plate and syncoxae. While all other described nymphs of the subgenus Sternalixodes have sternal plates, no members of the subgenus other than I. myrmecobii have also been recorded with syncoxae.

Figures

FIGURES 1 – 4. Ixodes myrmecobii Female. 1 Dorsal view, 2 Ventral view, 3 Dorsal capitulum, 4 Ventral capitulum.

FIGURES 12 – 13. Ixodes myrmecobii Female scanning electron micrographs. 12 Dorsal view, 13 Ventral view.

FIGURES 5 – 11. Ixodes myrmecobii Female. 5 Scutum, 6 Coxae and trochanters, 7 Spiracular plate, 8 Tarsus I, 9 Tarsus II, 10 Tarsus III, 11 Tarsus IV.

FIGURES 14 – 17. Ixodes myrmecobii Male. 14 Dorsal view, 15 Ventral view, 16 Dorsal capitulum, 17 Ventral capitulum. (PP = pregenital plate; MP = median plate; ADP = adanal plate; ANP = anal plate)

FIGURES 24 – 25. Ixodes myrmecobii male scanning electron micrographs. 24 Dorsal view, 25 Ventral view.

FIGURES 18 – 23. Ixodes myrmecobii Male. 18 Spiracular plate, 19 Coxae and trochanters, 20 Tarsus I, 21 Tarsus II, 22 Tarsus III, 23 Tarsus IV. (PP = pregenital plate; MP = median plate; ADP = adanal plate; ANP = anal plate)

FIGURES 26 – 30. Ixodes myrmecobii Nymph. 26 Dorsal view, 27 Ventral view, 28 Coxae and trochanters, 29 Dorsal capitulum, 30 Ventral capitulum.

FIGURES 36 – 37. Ixodes myrmecobii nymph scanning electron micrographs. 36 Dorsal view, 37 Ventral view.

FIGURES 31 – 35. Ixodes myrmecobii Nymph. 31 Scutum, 32 Tarsus I, 33 Tarsus II, 34 Tarsus III, 35 Tarsus IV.

FIGURES 38 – 40. Scanning electron micrographs of the trochanters of Sternalixodes males. 38 Ixodes holocyclus, 39 Ixodes myrmecobii, 40 Ixodes cornuatus.