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Long known as the Argentine horse tick because the source of the original specimen was stated to be Valparaiso, this tick has never been reported from South America. Why Valparaiso has been referred to Argentina and not to Chile is uncertain. As early as 1907, Donitz questioned the South American origin of this species, remarks that were overlooked by most subsequent writers. According to Dönitz (1910B), Winthem was a Hamburg dealer (presumably in zoological specimens HH).

Symbiotes were not discovered in M. Winthemi by Cowdry (1925C, 1926A, 1927).

Schulze (1938A) mentioned this species in his study of adult development within nymphs and in his 1943B study. Jakob (1924) included M. winthemi in his study of tick genera as have all authors who have discussed this subject. Because of its remarkable appearance, this species has been widely illustrated and discussed, usually largely incorrectly.

The first reference to this tick in South African literature (Theiler, correspondence) is that of Orpen (1904): "It is com monly believed here that there are no ticks in the Barkly East district, or only such as are brought in by transport cattle during the Summer and that ticks will not survive the severity of our winter hosts. I may state that last Winter I found many ticks upon our veld fed horses and that this winter they are worse, in a troop of about seventy mares and foals, many animals are fairly covered with ticks. We have had severe frosts since the beginning of April and the mountains are white with snow. This would lead one to conclude that given the protection and the warmth of an animal's body these ticks will live through any New England (Barkly East district) winter. (It is noticeable that the variety found on our horses remain upon them when molto ing).

The original description of the genus, translated from German, is as follows: Margaropus gen. nov. Body slender, longer than wide, sides slightly sinuously rounded, the posterior mar. gin on each side bearing three small, pointed hairtufts. The second and third pairs of legs are normal (the first pair is lacking), the fourth has very large, flat, sharply separated, almost circular segments. Type species: M. winthemi sp. nov.

The count of three pairs of pointed hair tufts noted by Karsch for M. winthemi was probably due to the dry, greasy, rubbed condition of the specimen. Fresh specimens bear six pairs of posterior hair tufts; these are not pointed.

Subsequently, the generic description of Margaropus presented by most writers has included the statement that the adanal shields are joi led anteriorly, a fact true for M. winthemi, though dif. ficult to discern in many specimens, but not true for M. reidi sp. nov.

The genus may be redefined as follows: Males with expanded leg segments that are more or less deeply separated from each other (partially noncontiguous); adanal shields arising at level of coxa IV and extending posterior of anus; tarsi elongate, narrow, tapering, with a large, apical, hooklike projection; palpi intermediate between those of Boophilus and Rhipicephalus, not ridged as in former genus; integument with conspicuous hairs posteriorly; with eyes (may be indistinct in M. Winthemi); un ornamented. Females with leg segments not greatly widened but other leg characters similar to those of male. Palpi intermediate between those of Rhipicephalus and Boophilus. Eyes distinct.

DISEASE RELATIONS

Although circumstantially associated with babesiosis, Babesia bigemina, no actual relation of this tick to any pathogenic organism has been demonstrated.

DENTIFICATION

MALE: Length overall up to 3.7 mm., width 2.5 mm.; color reddish brown; outline oval with integument bulging beyond scu tum laterally and posteriorly; with caudal protrusion when en gorged.

Capitulum: Basis capituli approximately twice as wide as long, lateral margins curved, basal margin concave; bearing a

horizontal row of eighteen to twenty hairs at level of midlength; ventrally with straight posterior and lateral margins, the latter converging basally. Palpi: Overall length and width of each palpus approximately equal dorsally; segment I just barely visible dorsally, longer ventrally; segment 2 quadrate with a slight an gular projection at the inner basal juncture, length one_third greater than that of segment 3; segment 3 compressed, semicircular, with broadly pointed outline distally; ventrally segment 3 with a broadly triangular retrograde spur. Hypostome twice as long as wide, apex rounded with a slight medial notch and with distinct corona; dentition 4/4, with five or six den ticles in inner files increasing to nine or ten denticles in outer files.

Scutum: Outline slightly convex laterally, more acutely converging anteriorly, bluntly rounded posteriorly; two-thirds as wide as long. Posteromedian groove shallow, narrow, elongate; paramedian grooves similar but shorter; cervical grooves convergent anteriorly, thence divergent for three_fourths of their length, extending one-third of scutal length. Hairs on scutum pale, shorter than lateral hairs; numbering about twelve in each scapular area and about twenty anteriorly between the cervical grooves; a row in place of the outline of the female scutum; others scattered in irregular lines on posterior half of scutum; a few rows of longer hairs on integument beside scutum, those posterior of the spiracular plates forming six pairs of longer hair tufts each clump of which consists of five to ten hairs. Eyes extremely indistinct; small, flat, situated on lateral mar. gin at the level of coxa II.

Spiracular plate subcircular, with two rows of large goblets encircling the aperture. Genital aperture situated at level of anterior half of coxae II; outline broadly rounded anteriorly, gradually converging laterally, bluntly angled posteriorly. Genital grooves mildly undulating from aperture to anus, thence widely divergent to spiracular plates. Preanal shield with broadly to narrowly rounded anterior margin, situated between genital grooves from level of posterior half of coxae IV to anus, projecting beside anus as two tapering, narrowly pointed, robust spurs (adanal shields); accessory shields absent. Hairs on integument between genital grooves and coxae arranged in three irregular rows extending from level of coxa I to spiracular plate;

about five irregular rows within genital grooves; two irregular rows of widely spaced hairs between level of anus and posterior margin. Ventral hook situated medially at posterior margin, on caudal protrusion of engorged specimens, articulated to body basally, free from base to apex; twice as long as wide; anterior margin straight; lateral margins parallel, posterior margin bluntly rounded.

Legs: Coxae equidistant from each other, almost contiguous; outline of each with rounded junctures, I and IV subtriangular, II and III subquadrate; IV with a slight, indistinct blunt spur posteriorly near the outer margin; I with a similar spur and a slightly raised ridge at the apical juncture; coxa I without a pointed dorsal projection visible from above. Free segments of legs I and II subequal, those of III slightly larger, those of IV enormously widened; segments partially joined giving legs a "beaded" appearance especially on legs III and IV; constriction between first and second segment of each leg especially narrow; several conspicuous irregular rows of long pale hairs on dorsal surface of each segment, forming tufts at apex of segments on III and IV; an apical row of hairs encircling most segments, a few lateral and ventral hairs also present. Tarsi clawlike, with a narrowly pointed apex and small subapical spur ventrally; claws articulated dorsally and subapically, strongly recurved around pads.

FEMALE: Notably differing from male in that free segments of legs, while robust, are not greatly enlarged; also lacking a ventral book and conspicuous lateral hairs and hair tufts. Other characters recall those of the male.

Length of engorged specimens reaching 6.6 mm.; width 3.9 mm.; color, when wengorged, yellowish.

Capitulum: Basis capituli three times as wide as long, lateral margins strongly convex, posterior margin very slightly concave; porose areas large, ovate, situated directly posterior of each palpus; ventral outline similar to that of male but with lateral margins more acutely angled. Palpi slightly longer than wide; larger than those of male; segment 3 approximately three-fourths as long as segment 2; apex subcircular; ventral ly segment 3 with a very slight ridge in place of the retrograde

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spur of the male. Hypostome larger than that of male and with seven or eight denticles in inner files and ten or eleven denticles in outer files; otherwise similar to that of male.

Scutum: Length_width ratio approximately equal, lateral margins gradually tapering from scapulae to eyes and from eyes to bluntly rounded posterior margin. Eyes oval, slightly arched, more distinct and larger than in male, situated on lateral margin at widest point of scutum. Cervical grooves curved around eyes and extending to posterolateral margin distally; delineating a broad median, slightly shagreened field bearing widely scattered, short hairs.

Spiracular plate subcircular, with three rows of large gob lets encircling the aperture. Genital aperture shield shaped, in same position as in male. Genital grooves similar to those of male to level of anus, where they continue as slightly convex grooves extending almost to the posterior margin of the body. Hairs in lines similar to those of male except that these lines extend almost to posterior margin of body; hairs laterally only slightly longer and denser than ventrally.

Legs robust but not markedly modified. Coxae similar to those of males except that they are wider in relation to length and the spurs and ridges are even more reduced. Free segments with marked constriction between first and second segment similar to that of males. Tarsi longer and narrower in comparison to those of males but otherwise similar; claws and pads similar to those of males.

NYMPH and LARVA: Undescribed.

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