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Taxonomy

Overview

Ticks as well as the closely related mites belong to the same phylum (Arthropoda) as insects. The major difference between ticks and gamasid mites is the occurrence of a hypostome as the ventral mouthpart and the presence of a distinct sensory apparatus, the Haller's organ. With more than one million species the Arthropoda combine the largest phylum within the animal kingdom.

The subphylum Chelicerata includes the class Arachnida, which again contains several subclasses. The subclass Acari (syn. Acaria, Acarina, Acarida) includes ticks1.

Taxonomy

Classification	e.g.Dermacentor variablis
Kingdom	Animalia
Phylum	Arthropoda
Class	Arachnida
Subclass	Acaria (Acari, Acarina, Acarida)
Order	Anactinotrichidea (= Parasitoformes)
Suborder	Ixodida (= Metastigmata)
Family	Ixodidae
Genus	Dermacentor
Species	Dermacentor variablis

A characteristic of the Acarines is the extreme fusion of body segments, in contrast to the known three body segments head, thorax and abdomen in insects. The Acarine idiosoma assumes functions parallel to those of the abdomen, thorax and portions of the head in insects. The podosoma (the leg-bearing portion) and the opisthosoma (the portion behind the legs) form the idiosoma. Further, the mouthparts, located on the head (capitulum) are called the gnathosoma.

Body segments of ticks

The Acari are subdivided into the order Parasitiformes and Acariformes. The order Parasitiformes to which ticks belong have stigmatal pores on the podosoma part and free articulated coxae^1.

Their suborder is Metastigmata, because their stigmen can be found behind the coxa III or behind coxae IV. The members are obligate blood-sucking parasites. All of them have in common the Haller's organ, a complex sensory organ, on tarsus I, a toothed hypostome, a peritreme around the stigmen and chelicera of only two joints.

All adult Metastigmata mate on their host, before lying eggs on the ground. These develop into 6 legged larvae, 8 legged nymphs and adults.Adult ticks size span between 2,2 mm (unfed male) to 13 mm (fed female).

In the most common ticks feeding takes place on pet animals.

Typical characteristics of ticks

All stages of the developmental cycle of all kind of ticks parasitic on vertebrates
Stigma behind coxa IV
Ventral toothed hypostom
Peritreme around the stigmen
Haller`s organ on tarsus I
Stages: larvae, nymphs, adults
Ixodidae (Hard ticks) and Argasidae (Soft ticks)

The order Metastigmata comprises 3 families: the Ixodidae (hard ticks), the Argasidae (soft ticks), and the Nuttalliellidae. The two major tick families are Ixodidae and the Argasidae², Nuttalliellidae represents only one single species (N. namaqua; found in South and South-West Africa as a parasite of small mammals).

Diagram illustrating systematic and evolutionary relationships in ticks (from Keirans JE, Georgia Southern University, USA)

The accurate identification of tick species is an important factor in the detection and diagnosis of tick-borne diseases and is a prerequisite for tick control⁴.