Rhipicephalus pusillus Gil Collado, 1936

Estrada-Peña, Agustin, Venzal, José M. & Nava, Santiago, 2018, Redescription, molecular features, and neotype deposition of Rhipicephalus pusillus Gil Collado and Ixodes ventalloi Gil Collado (Acari, Ixodidae), Zootaxa 4442 (2), pp. 262-276: 263-267

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https://doi.org/10.11646/zootaxa.4442.2.4

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lsid:zoobank.org:pub:19E626C8-13F1-459D-987F-3A24089282F5

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http://treatment.plazi.org/id/03F28794-1510-BF08-B7E2-F98BFAABF827

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Rhipicephalus pusillus Gil Collado, 1936
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Rhipicephalus pusillus Gil Collado, 1936  . Redescription

Male. ( Figure 1 View Figure , A–G). Ten specimens measured. Length from scapular apices to posterior idiosomal margin 1.48–1.74 (1.52) long, breadth 0.88–1.03 (0.92); ratio length/width 1.61–1.69 (1.65) ( Fig. 1A View Figure ). Eyes at a level slightly behind coxa II. Dorsal punctations small to medium, few and scattered over central portions of conscutum; more abundant in posterior part of conscutum, over posteromedian and posterolateral grooves. Cervical fields shallow but present. Marginal lines long, shallow and marked by some punctations, beginning behind eye level, and delimiting first festoon. Actual posterior limit of marginal lines usually diffuse and difficult to determine; occasionally enclosing one festoon on one side and two festoons on the other in the same specimen. Scapular areas and areas lateral to marginal lines relatively free of punctations. Posteromedian groove wide and longer than posterolateral grooves, which appear as irregular depressions with an oval or subcircular shape. Adanal plates two times longer than broad ( Fig. 1B View Figure ), curved inwards medially, without pointed projections in medial margin, with posterior margin widely convex. Accessory adanal plates slightly visible, with posterior margin not separated from cuticle. Spiracular plates elongate ( Fig. 1C View Figure ), caudal prolongation narrow and straight, slightly visible from dorsal view, like small virgule, clearly smaller than size of each festoon. Perforations on spiracular plate very small, slightly denser in margins of plate, with narrow peripheral portion of plate which is devoid of perforations. A few slightly larger goblets present in central portions of spiracular plate, surrounding spiracle and extending over caudal prolongation.

Gnathosoma dorsally ( Fig 1D View Figure ) slightly broader than long, but as long as broad in a few specimens. Dorsally, length from palpal apices to posterior margin of basis capituli 0.36–0.43 (0.41), breadth 0.42–0.45 (0.44). Ratio of gnathosomal length/width 0.92–0.95 (0.93). Basis capituli 0.19–0.22 (0.21) long. Basis capituli dorsally hexagonal. Basis capituli dorsally with postero-lateral margins concave, but in some specimens very slightly curved or even essentially straight. Cornua very small, 0.013 long. Ventrally, basis capituli with posterior margin broadly convex, with two large lateral processes that in some specimens may overlap the coxa I. Palpi 0.21–0.23 (0.21) long, 0.33–0.34 (0.34) broad, rounded apically. Ratio of palpal combined length/width 0.61–0.64 (0.63). Ventrally, palpal segment I with a triangular process posteriorly directed ( Fig. 1E View Figure ), covering most of ventral surface of first palpal segment. In most specimens, this palpal triangular process is slightly directed posterolaterally. Palpal segment III ventrally with short, very pointed, and essentially straight chitinous spur, slightly curved in some specimens, directed backward. Hypostome ( Fig. 1F View Figure ) 0.29–0.31 (0.29) long, 0.09–0.1 (0.1) broad. Ratio of hypostomal length/ width 2.8–2.9 (2.9). Dental formula 3/3 with 8–10 rows of hypostomal teeth and a small apical corona.

Legs moderately short. Coxae I to IV of similar size ( Fig. 1G View Figure ). Coxa I with two large spurs, subparallel, internal spur almost two times wider and slightly shorter than external. Coxae II to IV with only external spurs, of slightly decreasing size from coxae II to IV. Trochanter I with very small spur, posteriorly directed.

Female. ( Figure 1 View Figure , H–N). Nine unengorged specimens measured. Length from scapular apices to posterior idiosomal margin 1.52–1.89 (1.67), breadth 0.92–1.05 (1.01). Ratio of total length/width 1.61–1.69 (1.65) ( Fig. 1H View Figure ). Length of the scutum 0.90–0.95 (0.91), breadth 0.90–0.94 (0.92). Ratio of the scutal length/width 0.98–0.99 (0.98). Posterior margin of scutum widely rounded. In some specimens, posterior margin slightly sinuous. Eyes mildly convex, placed on widest part of scutum, enclosed by few very small punctations, mostly posteriorly. Cervical fields scalpel-shaped, narrowly elongate but disappearing posterior to eye level. Scapular areas smooth, without punctations; numerous small punctations centrally and posteriorly on scutum. Genital aperture small and U shaped, at level of coxa II. Spiracular plate widely rounded ( Fig. 1J View Figure ), with curved, dorsal process, only slightly visible dorsally. Perforations in spiracular plate very small, with few, larger goblets randomly placed around spiracular plate.

Gnathosoma clearly broader than long. Dorsally, length from palpal apices to posterior margin of basis capituli 0.53–0.57 (0.56), breadth 0.60–0.65 (0.61) broad. Ratio of gnathosomal length/width 0.91–0.92 (0.91). Basis capituli dorsally 0.23–0.29 (0.27) long ( Fig. 1K View Figure ). Basis capituli clearly hexagonal, with posterior and lateral margins straight. Basis capituli with lateral projections at about mid-length, acute. Porose areas very small, about 2.5–3 times their own diameter apart. Cornua short, length 0.02. Palpi short, 0.31–0.32 (0.31) long, 0.42–0.44 (0.42) broad, rounded apically. Ratio of combined palpal length/width 0.73–0.74 (0.73). Ventrally palpal segment I ( Fig. 1L View Figure ) with very broad triangular process posteriorly directed, covering most of ventral surface of palpal first segment, and carrying 6–8 barbed setae. Hypostome ( Fig. 1M View Figure ) 0.23 long, 0.12 broad, with dental formula of 3/3 with 8–10 rows of hypostomal teeth and small apical corona.

Legs moderately short. Coxae I to IV of similar size ( Fig. 1N View Figure ). Coxa I with two large spurs, subparallel, internal spur two times wider and slightly shorter than external spur. Coxae II to IV only with external spurs, of slightly decreasing size from coxae II to IV.

Nymph. ( Figure 2 View Figure , A–G). Twenty unengorged specimens measured, molted in the laboratory from fed larvae collected on O. cuniculus  . Length from scapular apices to posterior idiosomal margin 0.84–0.93 (0.91), breadth 0.62–0.75 (0.71) ( Fig. 2A View Figure ). Ratio of total length/width 1.24–1.31 (1.28). Scutum 0.39–0.45 (0.40) long, 0.44–0.49 (0.46) broad. Ratio of scutal length/width 0.83–0.89 (0.86). Posterior margin of the scutum widely rounded. Eyes mildly convex, placed on widest part of conscutum, exactly on lateral angles of widely convex posterior conscutal margin. Cervical fields relatively long and narrow, depressed, reaching posteriorly to eye level. Ventral surface as illustrated ( Fig. 2B View Figure ). Spiracular plate widely rounded ( Fig. 2C View Figure ) with small and slightly pointed dorsal process, not visible dorsally. Spiracular plate with only one row of goblets located in periphery, with a few, larger goblets over spiracular plate.

Gnathosoma clearly broader than long, dorsally, length from palpal apices to posterior margin of basis capituli 0.23–0.26 (0.25), breadth 0.29–0.34 (0.33) ( Fig. 2D View Figure ). Ratio of gnathosomal length/width 0.72–0.75 (0.73). Basis capituli 0.10–0.11 (0.10) long. Basis capituli clearly hexagonal, posterior and lateral margins straight or slightly concave. Basis capituli with lateral projections at about mid-length, acute. Cornua absent. Palpi short, 0.14–0.16 (0.14) long, 0.22–0.25 (0.23) broad, tapered apically. Ratio of combined palpal length/width 0.59–0.60 (0.60). Ventrally ( Fig. 2E View Figure ) auriculae long, triangular and straight. Palpal segment I with broad and short triangular process posteriorly directed. Palpal segment III with chitinous ridge. Hypostome ( Fig. 2F View Figure ) 0.10 long, 0.06 broad (ratio 1.66); dental formula of 2/2 with 7–8 hypostomal teeth and an apical corona.

Legs moderately short. Coxae I to IV of similar size ( Fig. 2G View Figure ). Coxa I with two large spurs, separated, not parallel, internal spur almost same length and breadth as external spur, or slightly larger. Coxae II to IV only with external spurs, of decreasing size from coxae II to IV.

Larva. ( Figure 2 View Figure , H–M). All larvae were obtained from eggs laid by two engorged females collected on O. cuniculus  . Measurements are based on 15 specimens. Because of the small variability in setal measurements, well below the fourth decimal figure, we refer only to the average of these measurements. Denominations of setae follows Clifford and Anastos (1960) and Clifford et al. (1973). Length from scapular apices to posterior idiosomal margin 0.30–0.35 (0.32), breadth 0.24–0.27 (0.26) ( Fig. 2H View Figure ). Ratio length/width 1.22–1.25 (1.23). Scutum clearly wider than long, 0.10–0.12 (0.11) long, 0.21–0.24 (0.22) broad. Ratio scutal length/width: 0.49–0.50 (0.50) Posterior margin widely rounded in its median portion, with posterolateral margins essentially straight. Eyes small, placed on widest part of conscutum, exactly on lateral angles of posterior conscutal margin. Scutal setae: 3 pairs (Sc1–Sc3), measuring 0.016, 0.015, and 0.018, respectively. Alloscutal setae: 12 pairs. Four pairs of central dorsal setae (Cd1: 0.037, Cd2: 0.034, Cd3: 0.039, Cd4: 0.037), 7 pairs of marginal dorsal setae (Md1: 0.092, Md2: 0.096, Md3: 0.099, Md4: 0.066, Md5: 0.069, Md6: 0.059; Md7: 0.044) and 1 pair of supplementary setae (S: 0.051). Ventral surface as illustrated ( Fig. 2I View Figure ) with 13 pairs of setae plus 1 pair on the anal valves, i.e. 3 sternal setae (St1: 0.02, St2: 0.02, St3: 0.022), with St1 located below level of coxae I, St2 well below of coxae II and St3 between coxae III, 2 pre-anal pairs (Pa1: 0.034, Pa2: 0.034), 4 premarginal pairs (Pm1: 0.0 34, Pm2: 0.035, Pm3: 0.029, Pm4: 0.031), and 4 marginal ventral pairs (Mv1: 0.03, Mv2: 0.03, Mv3: 0.031, Mv4: 0.029).

Gnathosoma broader than long, dorsally, length from palpal apices to posterior margin of basis capituli 0.10–0.11 (0.10), breadth 0.11–0.12 (0.12) ( Fig. 2J View Figure ). Ratio gnathosomal length/width 0.90. Basis capituli 0.04 long. Basis capituli clearly rectangular, with posterior margin straight or slightly concave, then widely convex to blunt lateral projections at about mid-length. Palpi short, 0.08 long, 0.03 broad, tapered apically. Ventrally ( Fig. 2K View Figure ) palpal segment I with short chitinous ridge. Palpal segment III with faint chitinous ridge. Ventral basis capituli with two pairs of post-hypostomal setae (Ph1-Ph2), distance between Ph1 0.04 and Ph2 0.03; posterior margin of ventral basis capituli widely round. Auriculae absent. Hypostome ( Fig. 2L View Figure ) 0.04 long, 0.02 broad, with dental formula of 2/ 2 in every row but apical corona, with rounded apex, and all denticles sharply pointed, 8/10 denticles in row I, 7 in row II. Palpal setae: 7 on genu, i.e. 1 paraxial (Gp1), 2 antiaxial (Ga1–Ga2), 3 dorsal (Gd1–Gd3) and 1 ventral (Gv1); 6 on femur, i.e. 1 paraxial (Fp1), 2 antiaxial (Fa1–Fa2), 1 dorsal (Fd1) and 2 ventral (Fv1–Fv2); 10 on tibiotarsus (Ttt1–Ttt10); trochanter 0.

Legs moderately short. Coxae I to IV of similar size ( Fig. 2M View Figure ). Every coxa with one internal spur, coxa I spur largest. Coxa I with 3 setae, 1 anterior (CIa), 1 posterior (CIp) and 1 paraxial (CIpa); coxae II and III each with 1 anterior setae and 1 posterior seta; trochanters without spurs. Tarsus I length 0.20, width 0.09. Setae on tarsus I: group I 2, dorsal; 4 setae in group II – 2 dorsal (dII1, dII2), 1 lateral antiaxial (laII1) and 1 lateral paraxial (lpII1); 4 dorsal in group III (dIII1–4); groups IV and V dorsal setae absent; 2 dorsal in the group VI (dVI1–2). Ventral and lateral setae: 4 setae in group I – 2 ventral (VvI1–2); 2 lateral antiaxial (laI1) and lateral paraxial (lpI1); 4 setae in group II – 2 ventral (VvII1–2); 1 lateral antiaxial (laII2) and 1 lateral paraxial (lpII2); 4 setae in group III – 2 ventral (VvIII1–2); 2 lateral antiaxial (laIII1) and lateral paraxial (lpIII1). Haller’s organ with 3 phs setae plus 4 apparent setae in capsule.

Molecular features. The phylogenetic tree obtained from the 16S sequence places this tick in a large cluster that contains the R. sanguineus  group. It is however separated from Rhipicephalus bursa Canestrini & Fanzago, 1878  , in which R. pusillus  was placed after its original description as R. bursa pusillus  . Rhipicephalus pusillus  clusters apart from several species of the R. sanguineus  group, near Rhipicephalus rossicus Yakimov  and Kohl- Yakimova, 1911.

Hosts and distribution. Rhipicephalus pusillus  is presumed to be a three-host tick ( Walker et al., 2000). The European rabbit ( Oryctolagus cuniculus  ) is its primary host but the tick has also been reported feeding on other hosts summarized by Walker et al. (2000). The original description by Gil Collado (1936) is based on two females collected on Vulpes vulpes  , which seems either a consequence of predatory habits or the use by the fox of an abandoned rabbit den. The preferences of attachment sites on the rabbit and the seasonal dynamics on O. cuniculus  have been reported by Márquez and Guiguen (1992). This tick has never been collected by dragging, and the extensive data provided by Osácar (1992) on ectoparasites of rabbits, reported R. pusillus  as an exclusively endophilous species. Rhipicephalus pusillus  has been reported to feed extensively on livestock and C. elaphus in Spain ( Ruiz-Fons et al., 2006) and Walker et al. (2000) mentioned a female collected “on vegetation”. Guglielmone et al. (2014) consider birds to be valid but unusual hosts for this tick. The distribution of the tick is related to the original distribution of the European rabbit, including the Iberian Peninsula, southern France and Italy, Morocco and Tunisia (summarized by Walker et al., 2000).

Diagnosis and species relationships. Molecular features of 16S rDNA confirm that Rhipicephalus pusillus  is close to species that cluster into the R. sanguineus  group. It is however not closer to R. bursa  , the species for which it was originally described as subspecies, than to other species of the genus. While the specific epithet makes reference to its small size, identification of adults of this species based on size is not advisable, because specimens of other species of the genus may be abnormally small due to poor nymphal feeding period. The male has the dorsal surface with small and scattered dorsal punctations, with relatively short marginal grooves, not reaching the eyes, and reaching the first festoon (in a few specimens, marginal grooves do reach the second festoon). Ventrally, the male of R. pusillus  has wide adanal plates, two times longer than wide, internally concave and widely rounded posteriorly, without an internal spur, and accessory adanal plates difficult to observe and not projecting over the cuticle. The spiracular plates have a long narrow, straight process, which is slightly visible in a dorsal view in most (but not all) specimens. Coxae II to IV have only external spurs, which is diagnostic. The female has very small porose areas, separated by 2.5–3 diameters, very short cornua, and a large triangular spur on the ventro-internal side of the palpal article I, carrying 6–8 barbed setae, which is diagnostic. The nymph is unique in the ventral aspect of the basis capituli. The large auriculae of the nymphs of R. pusillus  are also present in nymphs of R. rossicus  and R. turanicus Pomerantzev, 1940  . However, R. pusillus  has two large spurs on coxa I, separated, not parallel, internal spur being slightly larger or of similar size than internal spur. The nymph of R. rossicus  has external coxal spurs only on coxae I–III. The nymph of R. turanicus  has the internal spur on coxa I clearly smaller than the external. The larva of R. pusillus  is more difficult to separate from close species, but has chitinous ridges on the ventral side of palpal segment I (absent in close species), lacks auriculae, and has a chitinous ridge on coxa III (absent in R. sanguineus  s.l.).

Specimens examined. The type specimens of R. pusillus  are lost (Sonia Olmeda, Faculty of Veterinary Medicine, Madrid, Spain, pers. comm.) therefore precluding further comparison with other specimens of other species. We therefore proceeded to the naming and deposition of a neotype. The neotype specimen is a male, collected in a burrow of Oryctolagus cuniculus in Pina de Ebro  , 41°29’50’’N, 0°29’12’’W (Spain), about 300 km away from the original type locality, by J.J. Osácar in May, 1990 (the original female holotype was collected on a fox, but European rabbit is widely accepted as its typical host). The specimen is deposited in the U.S. National Tick Collection, with accession number USNMENT00862202. The remaining specimens of this collection, 10 females, 8 males, 20 nymphs and 50 larvae were used to complete the redescription. Additionally, 3 females and 12 males (collected from O. cuniculus, in Almudévar  , Spain, 42°03°41’’N, 0°34’55’’W, J.J. Osácar coll.) and 19 semiengorged females and 24 males (collected from O. cuniculus, in El Rocío  , Spain, 37°07’30’’N, 6°28’05’’W, R. Segura coll.) were used to complete the redescription. Flat nymphs were obtained from engorged larvae collected with the same data as the neotype. Newly hatched larvae were obtained from several (uncounted) females collected on O. cuniculus  with the same details as the neotype. Specimens other than the neotype are deposited in the collection of the Faculty of Veterinary Medicine of Zaragoza (Spain) under the accession number FMV1411.