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Study of comparative morphology in the genus Rhi ce alus and of chaetotaxy in the family Ixodidae led Pomeran zev to reconstruct radially generic concepts of this family. This approach merits further investigation; however, the pitfalls of hasty conclusions based on worn or poorly..pm-eserved field collected specimens, in which the chaetotaaclc picture is imperfect, may result in aiditional confusion of species concepts (Hoog_ straal 19550).
Rhipicephalids tend to considerable variation in appearance and morphological details owing to crowding on the host, welfare of immature stages, and availability of suitable hosts, factors that play a part in the determination of size, robustness, and even certain physical characteristics. Distinguishing characters in many specimens tend to become so generalized that diagnosis is difficult. This is especially true for females. The question of biological races remains to be explored; many data suggest this phenomenon to be operable in certain groups of rhipicephalids. The genus is divided into clearly defined species and species variable enough to cause confusion. It contains extremely cormnon as well as rare species.
Host predilections within this genus are fairly wide among several groups of available animals, although the lack of interest in other animals easily available in the same area is conspicuous by rarity of records of their infestation. A few species, such as R. Eavus, have an exceedingly wide host range, being common. ly taken on man and all domestic and many feral animals, such as carnivores, antelopes, hares, birds, elephant shrews, elephants, buffalos, and others. Other species, such as R. distinctus from hyraxes, are known only from a single lcind of host. It is sig_ nificant that immatures and adults of most rhipicephalid species do not attack birds and reptiles.
The life cycle is either the two host or the three host type and hosts of immature stages may be either the same as those parasitized by adults or smaller and different animals. In some species, records of larvae from both cattle and rodents are so common as to confuse the picture of the preferred hosts of this
stage. H. a ndiculatus is an interesting example in point.
frequently found on other animals. Reasons for these differences are beyond our present ability to explain.
Immature stages of many rhipicephalid species remain un_ described and distinguishing criteria for a number of those that are known are insufficient for identification of field collected material.
Ecological stratification is quite restricted, various species being confined to forests, highlands, semidesert areas, or certain rainfall conditions. The degree and distribution of relative humidity appear to be the most critical of limiting factors. Vegetation types associated with this factor and in. fluenced by the length of the rainy season or proximity to moisture laden air beside the seas can often be associated with rhipicephalid distribution.
Economically, many species are of considerable importance as reservoirs an vectors of a variety of animal and some human pathogens. The kennel tick, R. s. san 'neus, has been shown to have a particularly wide spectruh of achhhl or potential relationships as a vector of diseases.
KEY TO SUDAN SPECIES OF RHIPICEPHALUS
Eyes convex or hemispherical, distinctly
furrowed laterally or protruding from a
depression ("orbited" ) . Coxa I with
distinct dorsal projection................................ ..2
Eyes flat or slightly rounded, not
Eyes hemispherical, in a depression
(orbited) . Adanal shields large,
enormously widened posterolaterally.
Scutum dark with dense medium and
large size punctations; color con.
treating with reddish body integument
and saffron legs. Frequently large
(about 5.0 mm. long). (Common through
mh Man)OQOIOQOQOOCQOIOOOICOIOOOIOQOilOIOORI ED Figure? 235 EEK
Eyes convex, with an encircling fur.
row. Adanal shields mildly rounded
laterally, not exceptionally large.
Color overall brownish. Scutum with
moderately numerous fine and medium
size punctations. Fairly smll (about
3.5 mm. long). (Southeastern PRAVUS Figures 255 aE"2'33
Coxa I with distinctly pointed dorsal projection*. (Localized areas in ~an)IOIIOICOIOUDUIQQQIIOIIIIQIQQIQIQIOQOOIOICOOQQL
Coxa I without a distinctly pointed
projection though a smaller, rounded
hump may be visible in its place.
(More or less widely distributed)..........................l1
R. simus group , a small parasite of canerats only,
_ sim soni _ typically Ears tfls projection but this projection is so small
and frequently so reduced that it is not considered distinct enough to include in this section.
Lateral grooves faint, absent, or
Lateral grooves distinct as such#............................8
Scutal punctations in more or less
definite rows of'R. simus type,
interstitials varIabI5'5Et always
insignificant in comparison with
Scutal punctations scattered, not
Posteromedian and paramedian grooves
absent. Adanal shields with inner
margin in a straight line centrally
and with a peculiar protrusion at
juncture of inner and posterior margins........................................R. LONGICOXATUS
Posteromedian groove long, narrow,
paramedian grooves shorter, wider,
less well defined. Adanal shields
with inner margin concave centrally
and its juncture with posterior I
Basis capituli sharply angled lat.
orally and with long cornua. Scutal
punctations large, unequal, unevenly
distributed, small laterally, larger anteriorly..........................................R. ARNOLDI
Basis capituli slightly convex lat.
ll latermyIQQOOOOIOOOOIOOOOOOOOOOOOOOOOO%éb~SI Figures 1 555 232
fR. distinctus atypically may have apparently shallow lateral grooves due to the size and depth of the row of large punctations in its bed.
Lateral grooves without prominent
punctations. Adanal shields with
both posterior marginal junctures
extended, the outer juncture spur_
like, the inner rounded or spurlike;
accessory shields distinct and pointed..........................................R. TRICUSPIS
Scutal punctations moderate size,
reticulate. (Common only in Yei
Figures ZZU ho ZZ2
Scutal punctations large , dense ,