Glossary of morphological features
Accessory shields/ plates
Accessory shields (also known as accessory plates) are located on the ventral surface of male ticks and are found as a pair of plates. They are found laterally to the adanal shields and are often much smaller in size than the adanal shields, however their shape and size (small or large) can vary between species and individuals within the same species. The genera that this feature can be found in are mainly Rhipicephalus, Hyalomma and Rhipicephalus (Boophilus).
Adanal shields/ plates
Adanal shields (also known as adanal plates) are a pair of plates that are located on the ventral surface of the male tick, directly lateral to the anus. The shape of the end of these shields is influenced by the posterior margin, which can cause the shields to have a squared or rounded end. The general shape of the adanal shields can vary, however in most species they are either a narrow trapezoid in shape or they can be broad and curved. Adanal shields or normally found in Ixodes, Rhipicephalus, Hyalomma and Rhipicephalus (Boophilus) males.
The anal groove is a small depression in the integument located on the ventral surface. It generally forms a loop around the posterior anus and can either be absent, indistinct or in the case of Ixodes, form an anterior loop around part of the anus. This feature can be found in both male and female ticks. As well as its position, its alignment can also be used in identification; possible shapes include long and parallel, diverging or short and converging. In some species the anal groove can form a circle around the anus.
Anal plates/ sub-anal plates
The anal plate is a sclerotized region surrounding the anus in male ticks. It is made up of two or three pairs of plates and can protrude noticeably after a male tick has fed. Anal plates are mostly found in Hyalomma, Rhipicephalus and Rhipicephalus (Boophilus) males; however Ixodes males have flat anal plates that do not protrude after feeding. As well as anal plates, there may be sub-anal plates present. These can vary in alignment and distinctness, depending on the species; however they are typical of Hyalomma males. Sub-anal plates are relatively small plates located posteriorly to the anal plates of male ticks and can either be in line with the anal plates or be located more laterally. Their distinctiveness can also vary from indistinct to distinct and can vary in colour from light to dark.
Auriculae are lateral protrusions found on the ventral surface of the basis capituli. They are generally only found in Ixodes and come in two forms; indistinct or distinct.
When using the basis capituli to identify a species there are two feature to look for, the first in the lateral angle of the basis capituli; this feature is particularly important in Rhipicephalus due to the six sided shape of the basis. If the angle is greater than 90º it is considered to be blunt (all Rhipicephalus males), whereas if the angle is less than 90º it is considered to be sharp, however there is difficulty in using this feature due to the articulation of the basis with the idiosoma.
The second feature is the lateral margin of the basis capituli, this feature not only varies between genera it can also vary between the sexes. The lateral margin can appear to be either straight, medium angular or distinctly angular.
The caudal depression is a feature seen in Hyalomma males, if the posterior of the dorsal surface is broadly convex, the caudal depression is absent. However if it is broadly concave then the caudal depression is present which is seen in all but one species of Hyalomma.
The caudal process is a protrusion of the central festoon varying in size located posteriorly on some male ticks. The most common genus this feature is seen in is Rhipicephalus and can be seen to be either absent, narrow or broad.
Cervical field depression/ shape/ texture
Cervical fields are paired depressions are found on the anterior scutum, posterior to and lateral to the join between the gnathosoma and idiosoma called the cervix. When looking at the cervical field depression, particularly close to the cervix, there may be cervical pits present. The depth of depression at this point is referred to as either not apparent or apparent.
As well as the depth of depression the shape of the depression can be useful in identification. The shape of the cervical field is caused by the outer scapular grooves and the inner cervical grooves. The shapes are described as absent, small, large/curved, large straight. This characteristic is particularly important when distinguishing between female Rhipicephalus species.
The final feature of the cervical field to look for is its texture. Located on the scutum are punctuations (discussed below), however there can be an additional texture present in some species. The texture is formed in the integument, within the base of the depression and is classed as either no wrinkles or wrinkled.
Cervical grooves are also associated with the cervical field and they form the medial boarder of the cervical field and can be found in both sexes. The depth to which the cervical grooves depress can depend on the species.
The cornua are a pair of projections found on the dorsal side of the basis capituli and can be classed as indistinct or distinct, depending on the species.
In most species of tick the coxae show a uniform colour, however in some species of Ixodes there can be a characteristic known as syncoxae, where the posterior part has a lighter colour or texture. A range of different shaped spurs can be found on the coxae. The first spur to look for is the anterior spur located on coxa 1, this spur is viewable from the dorsal surface when it is present, however the smooth edge of the first coxae may also be viewable from the dorsal surface in some species. On the ventral surface a number of different spurs may be present on the coxae. These spurs are classed as either internal or external spurs, internal spurs on coxae 1 can be classed as either long or short (e.g. I. ricinus vs. I. hexagonus). In some species there may be paired spurs (both external and internal) on coxae one, in these species the spurs can appear either as indistinct bumps or distinct spurs. As well as the distinctiveness, the length of these spurs is also important and as with the single internal spurs, they can be either short or long. The final characteristic of coxal spurs on the first coxa to look for is the pairing of the spurs which can be either absent/small/unequal or large/equal.
External and internal spurs located on the rest of the coxae (two to four), when present can also vary in size; ranging from short to medium. As well as their length, they can also vary in distinctiveness, again ranging from indistinct bumps to distinct. The final feature of importance when identifying species is coxa four. The coxa itself can range in size from normal (as seen in most species) to very large, which is often seen in Dermacentor species. The final feature of coxa four is the presence and size of an internal/external spur. As with coxa one, the spur (when present) can range in size from short to long and is often seen in Haemaphysalis species.
Eyes can be variable between genera; they range from absent/distinct, flat or slightly convex, distinctly convex to very convex. They can also vary in the positioning on the scutum, depending on the shape of the scutum.
Festoons (central festoon, parma and paracentral festoons)
Festoons are largely variable; they can vary in presence, number and arrangement. When festoons are present, they can be present in both male and female. In most species where festoons are present, they are regular in size and start posterior to the spiracle plate and can range in number from nine to eleven. However in some species the central festoon may be enlarged and appear as a distinct structure from the rest of the festoons (a feature often seen in species of Rhipicephalus), this structure is called the parma. Additionally to this there may be a series of bulges associated with the festoons lateral to the central festoon called paracentral festoons. These bulges may be seen to be separate anteriorly or joined anteriorly, forming an arch (a feature seen only in Hyalomma anatolicum excavatum).
The position and shape of the genital aperture is particularly important when distinguishing between closely related species e.g. Ixodes ricinus and Ixodes persulcatus. The aperture itself can have numerous shapes; narrow ‘U’, broad ‘U’, narrow ‘V’, truncated ‘V’ or broad ‘V’. As well as the shape of the aperture itself, the shape of the genital aperture anterior groove can also vary from shallow to deep. The position of the genital aperture can vary, mainly between coxae 3 and coxae 4.
The lateral grooves are long indentations of varying size visible on the dorsolateral surface. They are often found in species that have festoons and are considered to be either indistinct (line of punctuations) or distinct (deep groove). Lateral grooves can also vary in length, varying between long and short and finally their texture can also vary; smooth, wrinkled or distinctly punctate.
This characteristic is particularly important when distinguishing between species of Hyalomma, some species will have pale coloured bands however most species do not. As well as coloured bands, some species (not necessarily Hyalomma may have dark coloured legs or reddish coloured legs).
Ornamentation is a pattern on the scutum, which can be simple colours (as seen in Dermacentor reticulatus) or as areas of bright colour, often red/orange/pink (often seen in species of Amblyomma) known as enamel.
Palps are made up of four segments known as articles, which can vary in shape and features. Starting with article one, which is located at the base of the palp, the internal margin can vary between species. In particular the internal margin may have certain characteristics that will allow for identification; no protuberance/long and slightly concave profile, no protuberance/short and distinctly concave profile or protuberance with either one or two comb-like setae on each protuberance.
Article two may have a dorsal spur, ventral spur or a lateral extension. All these features are considered either present or absent, except in the case of the lateral extension which is a characteristic of the genus Haemaphysalis and can be seen to be either small or large. However in the case of Haemaphysalis inermis the lateral extension is absent. Article two can also vary in size and shape which gives each genus it’s characteristic mouthparts. The size and shape of article two is compared to the other articles resulting in; all small, Article two broad or article two long.
Article three may have a ventral spur that projects towards articles one and two, however this is either present or absent. Finally article four is the smallest of all the articles and is located on article three, it does not have any physical features which can be used in identification, but is used merely for sensory purposes.
The porose areas are small circular/oval pitted areas that can be seen on the dorsal surface of the gnathosoma, just posterior to the palps of female ticks. Distance can vary between them, particularly in Rhipicephalus from narrow to broad and in other species the shape can vary from narrow oval to broad oval/circular.
Located on the dorsal surface of some males (particularly in Rhipicephalus) there may be a number of grooves that vary in number, length and depression depth. These grooves are normally found in three’s; the posteromedian groove with two paramedian grooves located either side. The paramedian grooves can either be absent, small or large grooves, compared to the posteromedian groove which can be absent, indistinct or distinct.
Posterior ridges are commonly found in Hyalomma males and are associated with the posterior grooves. They are absent or can be found as two or four, depending on the presence and depth of the posterior grooves.
Punctuations are pits located on the scutum of both males and females. They are highly variable in distribution, which can be sparse, dense or localized, distinctiveness which can be either distinct or indistinct and finally size which can be either small or large.
Scapular grooves are a pair of indentations that are located laterally on the scutum of female ticks and anteriorly on the conscutum of male ticks. The depth of the scapular grooves (when present) can vary between shallow and steep.
Features of the scutum (females) and conscutum (males) can vary between species in colour; pale yellow to dark brown, but the scutum can also vary in shape; smooth, slightly wavy or distinctly wavy. Finally in some species there may be setae present on the scutum/conscutum; however in preserved specimens these may be lost.
Located at the distal end of the limb, contains the Haller’s organ used as a sensory organ. Shape of the tarsus can aid in identification of species, especially with regard to the genus Ixodes.
Presence of a spur on the trochanter is particularly important when distinguishing between species of Haemaphysalis. In males the length of this spur can vary between short and long.
Ventral plates are located on the ventral surface, posteriorly in male ticks. When they are present they can appear as either indistinct or present and form the groupings of plates (adanal, sub-anal e.t.c.) around the anus, particularly in Hyalomma and Rhipicephalus males. The ventral plates may also have spurs which when present are either distinct or indistinct and may be visible from the dorsal surface when the male is unfed. Often these spurs become visible after the male has taken a blood meal.