First Description of the Immature Stages and Redescription of the Adults of Cosmiomma hippopotamensis (Acari: Ixodidae) With Notes on Its Bionomics

Abstract

Cosmiomma hippopotamensis (Denny, 1843) is one of the most unusual, beautiful, and rare tick species known to the world. All stages of this species possess a unique morphology, on the one hand making them easy to identify, while on the other they exhibit similarities to certain species of Amblyomma Koch, 1844, Dermacentor Koch, 1844, and Hyalomma Koch, 1844. Adults of C. hippopotamensis have been collected on only two occasions from their hosts, namely Hippopotamus amphibius L. and Diceros bicornis (L.), and have been recorded from only a few widely separated localities in East and southern Africa. Here, the larva and nymph are described and illustrated for the first time, while the male and female are illustrated and redescribed. Data on hosts, geographic distribution, and life cycle of C. hippopotamensis are also provided.

Cosmiomma hippopotamensis (Denny, 1843) is one of the most striking, but rarely collected, species of African ixodid ticks. In 1970, however, a locality in north–west Namibia, at which it was fairly abundant, was discovered, and numerous adult specimens were collected from the vegetation (Bezuidenhout and Schneider 1972). After this discovery, the first experiments on the feeding preferences of the adults were made, and most importantly, the nymphs and larvae were reared.

Over time, the taxonomic position of this tick has changed on numerous occasions. The male and female were originally described as separate species of the genus Ixodes Latreille, 1796; initially the female as Ixodes bimaculatus Denny, 1843 and thereafter the male as Ixodes hippopotamensis Denny, 1843. A year later Koch (1844) realized that I. bimaculatus and I. hippopotamensis are sexes of the same species. He, as a first reviser, assigned priority to the name I. hippopotamensis and placed it in the genus Amblyomma Koch, 1844, that is, Amblyomma hippopotami. Neumann (1899) initially corrected the name to Amblyomma hippopotamense but later placed it in the genus Hyalomma Koch, 1844, changing the combination of names to Hyalomma hippopotamense (Neumann 1906). After studying the type specimens and a reevaluation of their morphological characters, Schulze (1919) created an independent genus for this species, namely Cosmiomma Schulze, 1919, with I. hippopotamensis as the type species of the genus. According to Hoogstraal (1956), Zumpt (1951) sunk Cosmiomma under Dermacentor Koch, 1844. As a result Hoogstraal (1956) placed C. hippopotamensis in the genus Dermacentor and considered Cosmiomma a subgenus of Dermacentor. However, after an examination of the publication by Zumpt (1951), we were unable to confirm this nomenclatural change. Most workers now agree that Cosmiomma is a monotypic genus comprising the species C. hippopotamensis. Santos Dias (1958) after studying the original descriptions of I. bimaculatus and I. hippopotamensis decided that page priority should be given to the name Cosmiomma bimaculatum, and he therefore considered this name as valid for the species. However, as mentioned above, Koch (1844), as first reviser, had already given the name I. hippopotamensis priority, and consequently, according to the International Code of Zoological Nomenclature (1999 and previous editions), this binomen should be accepted as valid. Based on a study of the external morphology of the adults, Filippova (1997) considered Cosmiomma to be most closely related to the Rhipicephalus Koch, 1844 lineage. However, a later analysis, also based on morphological characters, indicated that Cosmiomma was more closely related to the Dermacentor lineage (Klompen et al. 1997). No molecular data have ever been obtained for this species.

After discovering reared specimens of nymphs and larvae in the J. B. Walker and United States National Tick Collections (USNTC), we decided to describe these stages and more exactly redescribe the adult stages to facilitate a better understanding of the phylogenetic position of C. hippopotamensis.

Materials and Methods

The material examined is summarized in Table 1. Both field-collected and laboratory-reared ticks were studied. The specimens that were examined are deposited in the USNTC (Georgia Southern University, Statesboro), the Gertrud Theiler Tick Museum at the ARC-Onderstepoort Veterinary Institute (ARC-OVI) (Onderstepoort, South Africa), Natural History Museum of Berlin (NHMB) (Berlin, Germany), and the personal East African tick collection of the late J. B. Walker (South Africa).

Table 1.

C. hippopotamensis, material studied

No. of ticksa				Host	Locality	Date	Collector	Acc. no.b
♂	♀	N	L
Kenya, Eastern Province
1	2			Vegetation	Makindu, Chale area	2 Jan. 1968	G.C. Backhurst	RML 50613
1				Vegetation	Makindu, Chale area	10 Nov. 1967	G.C. Backhurst	RML 51750
	1			Vegetation	Makindu, Chale area	10 Nov. 1967	G.C. Backhurst	RML 51749
Kenya, Coast Province
1				Vegetation	Mazinga Hill, nr. Voi	6 Nov. 1956	D.L.W. Sheldrick	JBWC
	1			Vegetation	Upper Tsavo	30 Oct. 1946		JBWC
Namibia, Kunene Region (Kaokoland)
8	8			Vegetation	Otjipembe	Mar. 1971	J.D. Bezuidenhout	RML 62898
3	3				Opowu, Otjijanjasemo	6 Jan. 1960	State veterinarian	OP 2703 i
8	11					Mar. 1971	J.D. Bezuidenhout	HHC
4	4	10	20	Reared in laboratory				RML 65717
1	1			Reared in laboratory				RML 122176
27	89	5		Reared in laboratory				HHC
10	15	50	300	Reared in laboratory				JBWCOP
No data
1	1							ZMB
67	136	65	320	Total

^aL, larvae; N, nymphs.

^bRML, US National Tick Collection; JBWC, Jane B. Walker East African Collection; OP, Onderstepoort Veterinary Institute Collection; HHC, Heloise Heyne Collection; JBWCOP, Jane B. Walker Collection at the Onderstepoort Veterinary Institute; ZMB, Museum of Natural History (Berlin).

The immature stages and the more delicate structures of the adults were mounted on glass slides and examined under a light microscope and also by means of a scanning electron microscope, and the macrostructures of males and females under a stereoscopic microscope. Measurements for the male and female are given in millimeters and those for the various features of the immature stages in micrometers. The measurements are arranged as follows: minimum–maximum (mean, n = number of specimens measured). All illustrations have been drawn by D. A. Apanaskevich.

Cosmiomma hippopotamensis (Denny, 1843) (Figs. 1–8)

Fig. 1.

C. hippopotamensis, dorsally (Namibia). (A) Male. (B) Female. Scale bar = 3 mm.

Fig. 8.

C. hippopotamensis, larva (Namibia). (A) Scutum. Scale bar = 100 μm. (B) Gnathosoma dorsally. Scale bar = 50 μm. (C) Gnathosoma ventrally. Scale bar = 50 μm. (D) Coxae. Scale bar = 50 μm.

♂ (redescription) (Figs. 1A, 2A, and 3). Conscutum (Fig. 1A): broadly oval, widest at mid-length; distance from scapular apices to posterior margin of conscutum 5.22–6.93 (6.04; n = 13), maximum width 4.27–5.60 (4.91; n = 13), ratio length to width 1.16–1.27 (1.23; n = 13). Coloration: ornate with light ivory or pale yellow enamelled patches grouped in six pairs marginally on a dark brown background, a single central patch anteriorly and a pair of medial patches; some patches may be connected with neighboring patches as illustrated; small enamelled patches on third and fourth festoons. Cervical grooves distinct, moderately deep; a pair of central depressions, and a second posterior pair that correspond to paramedian grooves; seven distinct festoons. Large punctations sparse, fine punctations dense, evenly distributed over scutum. Eyes (Fig. 1A): round, convex, at anterior one-seventh of scutal length. Setae sparse and short. Venter (Fig. 2A): as illustrated; setae numerous, short, somewhat longer along posterior margin of venter. Apron of genital aperture (Fig. 2A): at level of coxae II. Adanal plates (Figs. 2A and 3A): long and broad, subtriangular, posterior margin crenulate, length 1.51–1.92 (1.69; n = 13), width 0.91–1.27 (1.09; n = 13), ratio length to width 1.41–1.72 (1.56; n = 13); setae relatively dense, especially on posterior margin of plates. Genital groove (Fig. 2A): well-developed. Anal groove (Figs. 2A and 3A): indistinct short arch posterior to anus. Spiracular plates (Figs. 2A and 3B): positioned on ventral surface in unengorged specimens, subtriangular with mildly concave anterior margin, greatest diameter in anteroposterior plane, length 0.89–1.30 (1.11; n = 13), width 0.77–1.10 (0.95; n = 13), ratio length to width 1.00–1.40 (1.17; n = 13); dorsal prolongation short, perforated portion of dorsal prolongation broad, tapering to apex, central nonperforated portion with narrow projections giving it a jagged appearance; dorsal nonperforated portion of spiracular plate with whitish enamelling. Gnathosoma (Figs. 1A, 2A, and 3C and D): length from palpal apices to posterior margin of basis capituli dorsally 1.63–1.85 (1.76; n = 13), width of basis capituli 0.96–1.18 (1.09; n = 13), ratio length to width 1.53–1.72 (1.61; n = 13). Basis capituli (Figs. 1A, 2A, and 3C and D): dorsally subrectangular; posterior margin concave; cornua inconspicuous; lateral margins with whitish enamelling; ventrally subrectangular; posterior margin convex. Palpi (Figs. 1A, 2A, and 3C and D): elongate, relatively narrow; length (I–III segments) 1.08–1.27 (1.21; n = 13), width 0.38 – 0.48 (0.44; n = 13), ratio length to width 2.65–3.00 (2.78; n = 13), length of segments in descending order: 2, 3, 1, 4; segment I well-developed; segment II narrow at base and thereafter parallel-sided; segment III subrectangular; segments II and III with whitish enamelling on dorsal surfaces. Hypostome (Figs. 2A and 3D): club-shaped; dental formula 3/3; length 0.96–1.20 (1.07; n = 13), maximum width 0.38 – 0.46 (0.42; n = 13), ratio length to width 2.32–2.67 (2.54; n = 13). Legs (Figs. 1A and 2A): of medium length, robust; with extensive whitish enamelling mostly on dorsal and lateral aspects. Coxae (Figs. 2A and 3E): coxae I with long triangular widely separated, subequal internal and external spurs with narrowly rounded apices; coxae II and III each with larger triangular external spur and smaller internal spur; coxae IV with relatively long, triangular, subequal internal and external spurs. Genu and Tibia (Figs. 1A and 2A) with two rows of short projections ventrally. Tarsus I length 1.27–1.54 (1.43; n = 13); tarsus IV length 0.89 – 1.25 (1.11; n = 13); tarsi II–IV (Figs. 1A and 2A): with well-developed hook-like terminal projection. Pulvilli (Figs. 1A and 2A): very short.

Fig. 2.

C. hippopotamensis, ventrally (Namibia). (A) Male. (B) Female. Scale bar = 3 mm.

Fig. 3.

C. hippopotamensis, male (Namibia). (A) Adanal plates. Scale bar = 1 mm. (B) Spiracular plate. Scale bar = 0.5 mm. Arrows show orientation of spiracular plate (a, anterior; d, dorsal). (C) Gnathosoma dorsally. Scale bar = 0.5 mm. (D) Gnathosoma ventrally. Scale bar = 0.5 mm. (E) Coxae. Scale bar = 1 mm.

♀ (redescription) (Figs. 1B, 2B, and 4). Idiosoma (Figs. 1B and 2B): broadly oval, widest at mid-length; length from scapular apices to posterior body margin 6.74 – 8.55 (7.73; n = 14, unengorged females), width 5.32–6.84 (5.93; n = 14, unengorged females), ratio length to width 1.15–1.43 (1.31; n = 14). Scutum (Fig. 1B): long, margins diverge in anterior one-fourth of total length, thereafter gradually converging to narrowly rounded posterior margin, length 3.12–3.84 (3.56; n = 14), width 3.31–4.03 (3.83; n = 14), ratio length to width 0.89 – 0.97 (0.93; n = 14). Coloration: ornate, major portion of scutal surface covered with whitish or yellowish enamelling; two narrow, brown, strips extend from cervical pits to posterior scutal margin with anterolaterally directed branches arising from the middle of each strip, brown patches surround eyes, extending anteriorly along scutal margin with a branch directed posteromedially; anterolateral branch of cervical strip and posteromedian branch of eye patch may be connected. Cervical grooves distinct, relatively deep. Large brown punctations sparse, fine punctations dense, evenly distributed over scutum. Eyes round, convex, positioned at widest point of lateral scutal margins. Setae sparse and short. Alloscutum (Fig. 1B): as illustrated, with two ivory-colored to yellowish subcircular, raised, cuticular patches with smooth dorsal surfaces (these raised patches are absent on all specimens examined from Kenya), longitudinal diameter 0.90–1.13 (1.02; n = 11); 11 festoons. Setae of alloscutum short, numerous, mainly distributed in center and posterior surface; the majority of latter setae directed laterally and anteriorly. Venter (Fig. 2B) as illustrated; setae numerous, mainly distributed on posterior surface. Genital aperture (Figs. 2B and 4A): at level of coxae II, U-shaped; preatrial fold flat or concave. Genital groove (Fig. 2B) well-developed. Anal groove (Fig. 2B) indistinct short arch posterior to anus. Spiracular plates (Figs. 2B and 4B): suboval; positioned on ventral surface in unengorged specimens, greatest diameter in anterolateral–posteromedian plane in unengorged specimens, length 1.37–1.82 (1.65; n = 14), width 1.13–1.44 (1.26; n = 14), ratio length to width 1.19–1.46 (1.31; n = 14); dorsal prolongation short, perforated portion of dorsal prolongation broad, central nonperforated portion with long and narrow projections giving it a jagged appearance; dorsal unperforated portion of spiracular plate with whitish enamelling. Gnathosoma (Figs. 1B, 2B, and 4C and D): length from palpal apices to posterior margin of basis capituli dorsally 1.73–2.16 (1.99; n=14), width of basis capituli 1.13–1.44 (1.29; n=14), ratio length to width 1.46–1.61 (1.55; n = 14). Basis capituli (Figs. 1B, 2B, and 4C and D): dorsally subrectangular; lateral margins with whitish enamelling; posterior margin slightly concave with slight central indentation; cornua inconspicuous. Porose areas inwardly inclined, deeply sunken with clearly circumscribed borders, separated by a narrow elevation less than half their width. Basis capituli ventrally subrectangular; with convex posterior margin. Palpi (Figs. 1B, 2B, and 4C and D): elongate, relatively narrow; length (I–III segments) 1.27–1.70 (1.47; n = 14), width 0.43–0.53 (0.48; n = 14), ratio length to width 2.80–3.55 (3.08; n=14), length of segments in descending order: 2, 3, 1, 4; segment I well developed ventrally; segment II narrow at base and thereafter parallel-sided; segment III broad, subrectangular; segments II and III with whitish enamelling on dorsal surfaces. Hypostome (Figs. 2B and 4D): club-shaped; dental formula 3/3; length 1.13–1.42 (1.30; n = 14), maximum width 0.38 – 0.48 (0.45; n = 14), ratio length to width 2.62–3.11 (2.88; n = 14). Legs (Figs. 1B and 2B): of medium length, robust; with extensive whitish enamelling mostly on dorsal and lateral aspects. Coxae (Figs. 2B and 4E): coxae I with long, narrow, triangular, widely separated, subequal internal and external spurs with narrowly rounded apices; coxae II and III each with triangular larger external spur and smaller internal spur; coxae IV with relatively long, narrow, triangular internal and external spurs. Genu and Tibia (Figs. 1B and 2B) with two rows of short projections ventrally. Tarsus I length 1.56–1.90 (1.78; n = 13); tarsus IV length 1.27–1.68 (1.52; n=13); tarsi II–IV (Figs. 1B and 2B): with well-developed hook-like terminal projection. Pulvilli (Figs. 1B and 2B): very short.

Fig. 4.

C. hippopotamensis, female (Namibia). (A) Genital aperture. Scale bar = 0.5 mm. (B) Spiracular plate. Scale bar = 0.5 mm. Arrows show orientation of spiracular plate (a, anterior; d, dorsal). (C) Gnathosoma dorsally. Scale bar = 0.5 mm. (D) Gnathosoma ventrally. Scale bar = 0.5 mm. (E) Coxae. Scale bar = 1 mm.

Nymph (description) (Figs. 5 and 6). Idiosoma (Fig. 5A and B): suboval, widest at level of coxae III, distinctly narrowing posterior to spiracular plates, length of unengorged specimens from apices of scapulae to posterior body margin 1,760–2,000 (1,904, n = 5), width 1,400–1,640 (1,496, n = 5), ratio length to width 1.17–1.35 (1.27; n = 5). Scutum (Figs. 5A and 6A): length 771–835 (798; n = 5), width 874–938 (914; n = 5), ratio length to width 0.84 – 0.89 (0.87; n = 5); pentagonal, posterior margin broadly rounded, posterolateral depressions deep; cervical grooves distinct, deep. Setae ≈9 pairs, length 38–52 (45; n = 6). Eyes suboval, bulging, located on lateral margins of scutum at approximately its mid-length. Alloscutum (Fig. 5A): as illustrated. Dorsal setae numerous; setae in anterolateral field very long, length 164–198 (180; n = 5); setae in intermediate rows (between lateral and central rows) length 76–100 (92; n = 4); setae in central rows length 48 – 60 (53; n = 4). Venter (Fig. 5B): as illustrated; faint posterior anal groove. Ventral setae numerous; anal valves with three pairs of setae. Spiracular plates (Fig. 6B): oval, maximal length in dorso–ventral plane; few large perforations. Gnathosoma (Figs. 5A and B and 6C and D): length from hypostomal apex to posterior ventral margin of basis capituli 739 – 803 (774; n = 5), width at apices of dorsolateral projections 533–588 (561; n = 5); ratio length to width 1.32–1.45 (1.38; n = 5). Basis capituli (Figs. 5A and B and 6C and D): dorsally short and broad; dorsally and ventrally subtriangular, with short and blunt lateral projections. Posthypostomal setae one pair. Palpi (Figs. 5A and B and 6C and D): elongate, length 324–348 (339; n = 5), maximum width 86–98 (94, n = 5), ratio length to width 3.31–3.91 (3.63; n = 5); segment I well-developed, cylindrical, distinct suture between segments II and III, segment II the longest, narrow proximally and sharply expanding distally; segment I with one ventral seta, segment II with five dorsal and three ventral setae, segment III with five dorsal and two ventral setae, segment IV with ≈11 setae. Hypostome (Figs. 5B and 6D): length from apex to the level of posthypostomal setae 392–448 (425; n = 5), width at narrowest portion 118–136 (126; n = 5), ratio length to width 3.29–3.53 (3.37; n = 5); protruding anteriorly considerably beyond palpal apices, club-shaped, broadly rounded at apex, dental formula distal 2 rows 3/3, proximal rows 2/2, 8–9 denticles in files. Legs (Fig. 5A and B): moderate in length. Coxae (Figs. 5B and 6E): coxae I–IV with poorly developed, broadly arcuate external spurs, internal spurs virtually invisible; coxae I–IV each with three setae. Trochanters: lack spurs. Tarsus I: length 348–392 (379; n = 5). Tarsus IV: length 348–384 (369; n=5). Tarsi I–IV (Fig. 5A and B) with hook-like terminal projection.

Fig. 5.

C. hippopotamensis, nymph (Namibia). (A) Dorsal view. (B) Ventral view. Scale bar = 1 mm.

Fig. 6.

C. hippopotamensis, nymph (Namibia). (A) Scutum. Scale bar = 200 μm. (B) Spiracular plate. Scale bar = 40 μm. Arrows show orientation of spiracular plate (a, anterior; d, dorsal). (C) Gnathosoma dorsally. Scale bar = 100 μm. (D) Gnathosoma ventrally. Scale bar = 100 μm. (E) Coxae. Scale bar = 200 μm.

Larva (description) (Figs. 7 and 8). Idiosoma (Fig. 7A and B): suboval, widest at level of coxae III; length of unengorged specimens from apices of scapulae to posterior body margin 580 – 636 (614; n = 29), width 501–548 (529; n = 26), ratio length to width 1.10–1.23 (1.16; n = 24). Scutum (Figs. 7A and 8A): length 328–360 (346; n = 25), width 424 – 480 (456; n = 31), ratio length to width 0.73–0.78 (0.75; n = 25); pentagonal, posterior margin broadly rounded, posterolateral marginal depressions indistinct; cervical grooves as faint, shallow depressions. Setae three pairs, Sc₂ 32–40 (36; n = 15), Sc₃ 26–32 (29; n = 27). Alloscutum (Fig. 7A): as illustrated. Dorsal setae 10 pairs; two pairs of central dorsals, Cd₁ 24–30 (26; n = 24), Cd₂ 26–30 (28; n = 22); eight pairs of marginal dorsals, Md₁ 34 – 42 (39; n=30), Md₇ 24–31 (27; n=29). Large wax glands (=sensilla sagittiformia) present. Venter (Fig. 7B): as illustrated; faint posterior anal groove. Ventral setae 14 pairs plus one pair on anal valves; three pairs of sternals, St₁ 38 – 48 (42; n=31); two pairs of preanals, Pa₁ 34 – 42 (38; n = 24), Pa₂ 36 – 44 (40; n = 26); four pairs of premarginals; five pairs of marginal ventrals, Mv₁ 26–32 (28; n = 31). Gnathosoma (Figs. 7A and B and 8B and C): length from hypostomal apex to posterior ventral margin of basis capituli 224–268 (251; n = 27), width at apices of dorsal projections 156–184 (169; n = 31); ratio length to width 1.37–1.60 (1.49; n=27). Basis capituli (Figs. 7A and B and 8B and C): dorsally hexagonal, with very short and obtuse lateral projections; ventrally rectangular. Posthypostomal setae one pair, Ph₁ 22–30 (26; n = 20); distance between Ph₁ 52–66 (58; n = 30). Palpi (Figs. 7A and B and 8B and C): elongate, length 124–142 (137; n = 30), width 46–50 (48, n = 30), ratio length to width 2.64–2.96 (2.84; n = 30); segment I well-developed, cylindrical, distinct suture between segments II and III; segment I without setae, segment II with four dorsal and two ventral setae, segment III with five dorsal and one ventral setae, segment IV with ≈11 setae. Hypostome (Figs. 7B and 8C): length from apex to the level of posthypostomal setae 118–142 (136; n = 27), minimum width 48–56 (52; n = 28), ratio length to width 2.27–2.87 (2.62; n = 27); protrudes considerably beyond palpal apices anteriorly, club-shaped, broadly rounded at apex, dental formula 2/2 throughout length, six to seven larger denticles in files. Legs: moderate in length. Coxae (Figs. 7B and 8D): coxae I–III lacking spurs, coxae I sometimes with an indication of a slight thickening of the surface instead of spur; coxae I with three setae, coxae II and III with two setae each. Trochanters: lack spurs. Tarsus I: length 176–194 (186; n = 31), width 64–74 (69; n = 28), ratio length to width 2.50–2.87 (2.70; n = 28).

Fig. 7.

C. hippopotamensis, larva (Namibia). (A) Dorsal view. (B) Ventral view. Scale bar = 0.5 mm.

Type Specimens

Original description based on female (as I. bimaculatus) from Southern Africa and male (as I. hippopotamensis) from South Africa (Denny, 1843). Santos Dias (1958) found three males, one of which is the type of I. hippopotamensis, and six females, one of which is the type for I. bimaculatus, in the Natural History Museum (NHM) (London). Theiler (1962) stated that the type specimens of C. hippopotamensis are in the NHM (London) and NHMB (Berlin, Germany). Bezuidenhout and Schneider (1972) indicated that the types of C. hippopotamensis (one male and four females; No 43.19; Hippopotamus) are in the NHM (London). According to the type catalogues of the NHM (London) and NHMB, there are no type specimens of C. hippopotamensis in their collections (Moritz and Fischer, 1981, Keirans and Hillyard, 2001). We have been unable to confirm whether the type specimens still exist or not.

Synonyms

Ixodes bimaculatus Denny, 1843; Ixodes hippopotamensis Denny, 1843; Amblyomma hippopotami (Denny, 1843) Koch, 1844; Amblyomma hippopotamense (Denny, 1843) Neumann, 1899; Hyalomma hippopotamense (Denny, 1843) Neumann, 1906; Dermacentor (Cosmiomma) hippopotamensis (Denny, 1843) Hoogstraal, 1956; Cosmiomma bimaculatum (Denny, 1843) Santos Dias, 1958.

Etymology

We believe that the generic name Cosmiomma is derived from the Greek “cosmima,” meaning jewellery and “omma,” meaning eye, while the species epithet “hippopotamensis” comes from Hippopotamus, the host from which the type specimens possibly were collected.

Distribution

There are only a few definite localities at which C. hippopotamensis has been found, and these are all confined to sub-Saharan Africa (Fig. 9). It has been recorded in Angola (Cuando Cubango District: Tondo), Botswana (North–West District: Lake Ngami), Kenya (Makueni District: Makindu: Chale area; Teita District: Kangetchwa, Manyani, Mazinga Hill near Voi, and the Tsavo area), and Namibia (Kunene Region: Ekoto, Ohopoho, Ondjarrakagha, Otjiboronbonga, Otjijanjasemo, and Otjipembe) (Hoogstraal 1956, Serrano 1964, Bezuidenhout and Schneider 1972, Walker 1974; our data). The type specimens of I. hippopotamensis originate from South Africa, but since the late 1840s no C. hippopotamensis has been found in this country (Walker 1991). Both Neumann (1899) and Dönitz (1910) mention that specimens have been collected somewhere between Zanzibar and the Great Lakes, while Santos Dias (1960) assumed that C. hippopotamensis might occur in Mozambique. Arthur (1960) stated that unconfirmed specimens of C. hippopotamensis were reported from Tanzania (=Tanganyika). In the Nuttall tick catalog (Keirans 1985), three females (No. 1030) identified as “Amblyomma hippopotamensis or n. sp.” collected from grass and leaves in Deep Bay, Malawi, are mentioned. Unfortunately, this collection lot is listed as missing, and we cannot confirm the identity of these females.

Fig. 9.

C. hippopotamensis, map of geographical distribution.

C. hippopotamensis was originally discovered among the skins of some mammals collected for the Earl of Derby by Joseph Burke, a British naturalist. According to K.H. Hyatt, British Museum of Natural History (J. B. Walker, 1968, personal communication), the locality of the types collected by Burke was “in the interior of South Africa at the parallel of Lalagor.” This locality cannot now be traced. We can, however, speculate as to its approximate whereabouts. Burke arrived in Table Bay, South Africa, on 17 March 1840 and proceeded north into the interior of the subcontinent. During June 1840, he shot both a black rhinoceros and hippopotamus at a locality somewhere between ±25°44′ S, 27° 51′ E, and ±25° 59′ S, 27° 33′ E. We surmise that it is from these skins that the type was collected. The latitude of this spot is almost parallel to that of Maputo Bay, Mozambique (26° 00′ S, 32° 45′ E) (formerly known as Delagoa Bay, Baía da Lagoa [in Portuguese]). “Lalagor” thus possibly represents a miss-spelling of Delagoa. Based on this assumption, we believe that the type locality lies somewhere between 25° 59′ S, 27° 33′ E and 25° 44′ S, 27° 51′ E, and have accordingly indicated this on the distribution map (Fig. 9).

Hosts

There are only two host records for the adults—hippopotamus, Hippopotamus amphibius L., and black rhinoceros, Diceros bicornis (L.) (Denny 1843, Serrano 1964). It has also been suggested that rhinoceroses rather than hippopotamuses might be the preferred hosts for the adults of C. hippopotamensis (Bezuidenhout and Schneider 1972). The hosts of the immature stages remain unknown.

Life Cycle

C. hippopotamensis is a two-host tick. In 1960, six adult ticks were sent to Onderstepoort by Dr. J.D. Coetzee, the State Veterinarian at Ohopoho in the Kunene Region, Namibia. This stimulated further interest in this colorful tick, and in 1970, one of us (J. D. Bezuidenhout), encouraged by Dr. Gertrud Theiler, instituted a thorough search for it in Kaokoland, in the north-western corner of Namibia. The results of this quest, during which some 80 adult ticks were collected, persuaded Bezuidenhout and Schneider (1972) to visit the region. Here, they collected a further 114 adult ticks from the vegetation bordering footpaths used by rhinoceroses to get to springs. They attempted to feed some of these ticks on terrapins, tortoises, a monitor lizard, rabbits, and a goat without success, but were eventually successful in feeding them on a black rhinoceros.

Bezuidenhout and Schneider (1972) gave only a brief account of their tick-feeding experiments on the rhinoceros, and these studies will now be described in greater detail. They initially placed three male and four female ticks on the back of a hand-reared 14-mo-old black rhinoceros kept in a small enclosure at the Etosha National Park, Namibia. Within 10 min, five of these ticks had attached in the animal’s perianal region and the other two quickly attached to its body, from which they were later removed. In contrast, only one of the three ticks that were confined in a bag behind one of the animal’s ears ultimately attached. Four adult ticks that were put on the ground near the rhinoceros soon found the animal, climbed onto it and attached under its tail. Other ticks that had been liberated in the enclosure and that had climbed up a tree, also quickly transferred to the rhinoceros when it came into contact with twigs on which they were waiting.

The ticks on the rhinoceros were carefully examined three times daily. During the initial 48 h those attached under the animal’s tail changed their positions twice. Two, a male and a female, finally attached 2–3 cm within the anus. Three females completed their engorgement on the rhino and dropped off 8 d after their attachment. Only one of these females subsequently laid a large batch of fertile eggs. This batch was divided before the eggs hatched, part of it being retained at the Regional Veterinary Laboratory, Windhoek, Namibia, while the second part was sent to the late Dr. W.O. Neitz at Onderstepoort for further laboratory studies on the life cycle.

With the exception of one mouse, from which seven engorged nymphs were obtained, attempts by Neitz to feed the larvae on domestic fowls and white mice were unsuccessful. When placed on the ears of rabbits, however, both the larvae and the nymphs, to which they subsequently moulted, engorged successfully. After detaching from the rabbits, the engorged nymphs successfully moulted to adults. The life cycle of C. hippopotamensis, based on the studies of Bezuidenhout and Neitz, is summarized in Table 2.

Table 2.

Life cycle of C. hippopotamensis

Development stage	Development period (d)	Host species
Female engorgement	8	Black rhinoceros
Pre-oviposition	19
Oviposition (duration)	10
Larvae hatch	66–71
Larval and nymphal engorgement	25	Rabbits, mouse
Nymphs moult to adults	28–63

The two-host life cycle of C. hippopotamensis is similar to that of Hyalomma rufipes Koch, 1844 and Hyalomma truncatum Koch, 1844 in southern Africa. Large ungulates, including rhinoceroses, are the preferred hosts of the adults of the latter two species, and hares (Lepus spp.) of the immature stages (Norval 1982, Horak and Fourie 1991). The immature stages of H. rufipes also feed on birds and those of H. truncatum on murid rodents (Norval 1982, Matthee et al. 2007). In the laboratory studies conducted by Neitz and Bezuidenhout, the immature stages of C. hippopotamensis fed successfully on rabbits and on a single mouse, but not on domestic fowls. Extrapolating these results to the field, hares and murid rodents could prove to be good hosts for the immature stages at localities within which adult ticks are present.

The rapidity with which adult C. hippopotamensis placed on the young rhinoceros scuttled to its perianal region and attached, and with which the ticks placed on the ground, or that had climbed onto a tree, transferred to the rhinoceros, implies that rhinoceroses are a preferred host of the adults. In support of this theory, the ticks engorged and females detached from the rhinoceros and one of them laid fertile eggs. Furthermore, adult ticks collected in the field were encountered on vegetation along footpaths used by rhinoceroses to get to springs, whereas hippopotamuses do not occur in this area (Bezuidenhout and Schneider 1972). The closest hippopotamuses to these springs were present in the Kunene River ≈90 km upstream from one of the collecting sites.

Disease Relationships

The medical and veterinary importance of C. hippopotamensis remains undetermined.

Related Species

The adults of C. hippopotamensis superficially resemble some of those in the genera Amblyomma and Dermacentor because of the extent of ornamentation on the conscutum of males and scutum of females. Males can readily be distinguished from all African Amblyomma and Dermacentor species by the presence of adanal plates and the pattern of ornamentation on the conscutum. Females are distinguished from those of African Amblyomma and Dermacentor species by the pattern of coloration on the scutum and the presence (in Southern African populations) of large, circular, ivory-colored raised patches on the alloscutum. In addition, both sexes of C. hippopotamensis can be distinguished from all African Amblyomma species (except Amblyomma sylvaticum [De Geer, 1778]) by the presence of two posterior spurs on coxae II–IV and a generally shorter gnathosoma.

The morphology of nymphs is unique. A combination of the following characters will guarantee identification of C. hippopotamensis on the nymphal stage: scutum with deep posterolateral depressions, prominent eyes, numerous exceptionally long setae on the anterolateral fields of the alloscutum, hypostome considerably longer than palpi, rudimentary spurs on all coxae. Larvae are similar in appearance to those of Amblyomma and Hyalomma, but are readily distinguished from them by the following characters: hypostome considerably longer than palpi and the absence of spurs on coxae.