FNZ 4 - Eriophyoidea except Eriophyinae (Arachnida: Acari) -Morphology
Manson, DCM 1984. Eriophyoidea except Eriophyinae (Arachnida: Acari). Fauna of New Zealand 4, 144 pages.
(
ISSN 0111-5383 (print),
;
no.
04.
ISBN 0-477-06745-X (print),
).
Published 12 Nov 1984
ZooBank: http://zoobank.org/References/C249A0E0-4F66-431B-9DB6-5C01ACA8CF65
Morphology
A knowledge of structure is essential for correct diagnosis and classification. Typical eriophyoid mites are depicted in Figures 1 and 2. There are three main body divisions - the rostrum, the dorsal shield or cephalothoracic shield, and the abdomen.
THE ROSTRUM is an important structure in classification at the family level. It is of a beaklike form and directed downwards.
There are two main types of rostrum. In the first, found in the Diptilomiopidae, the rostrum is large in relation to the body and apically attenuate. Here we have the long-form oral stylet, in which the distal recurved portion is longer than the stylet base plus pharyngeal pump (Figure 12). In the Sierraphytoptidae and Eriophyidae, on the other hand, the rostrum is usually small relative to the body and the short-form oral stylet occurs (Figure 13), i.e., the distal recurved portion of the stylet is usually shorter than the stylet base plus pharyngeal pump. In some females (deutogynes) of the subfamily Aberoptinae the rostrum is unusual in terminating in a spatulate or shovel-nosed structure.
Keifer (1959a) investigated the eriophyoid rostrum and associated structures, and to know more of its form and function one should consult Keifer's article.
In many species, arising shortly before the rostrum termination there is an antapical seta. Its occurrence and length are of some assistance in species recognition.
THE CEPHALOTHORACIC SHIELD is sometimes known as the propodosomal or dorsal shield, or simply 'shield'. Usually it is triangular or semicircular, and bears a pattern of lines, granules, or broken lines which is distinctive for individual species. The pattern may vary slightly or differ in intensity in any given species, but it is an important diagnostic feature. Keifer (1952) recognises and names several of the principal lines on the shield - the median (usually running the full length of the shield), admedians, and submedians; these are depicted in Figure 7.
The cephalothoracic shield sometimes has a projection, the anterior shield lobe (Figure 2), the occurrence of which is an important character at subfamily and genus level. In a few instances the lobe is thin and flap-like; in Rectalox falita n. gen. sp. for instance it is almost rectangular. The lobe's variation in shape and prominence is of importance in species identification. In genus Aculus the protogynes have two small spines projecting from under the anterior margin of the lobe. (Note. Measurements of the dorsal shield exclude the anterior shield lobe, where this is present.)
The cephalothoracic shield may bear from one to four dorsal tubercles and setae, although a few species - e.g., Cecidophyopsis ribis and Calacarus carinatus - lack these completely. Most commonly, two tuberculate setae are situated near the posterior shield margin. So far, no species have been found in New Zealand with three setae, but when present the third seta is situated on the midline, near the anterior margin of the shield. A few species have four setae, for instance Phytoptus avellanae and P. rufensis. The direction and length of the shield setae has an important bearing on generic placement; for instance, in Aceria they are directed to the rear, in Eriophyes anteriorly, and in Phyllocoptes usually towards the midline.
THE ABDOMEN, the principal part of the eriophyoid body, usually tapers towards the rear, and is 'worm-like' - divided transversely into a number of superficial rings which in bud and gall mites are regular dorsoventrally. Free-living forms are less worm-like, and may have flattened abdomens with longitudinal ridges or grooves or lateral structures. They may also have the body clearly divided dorsoventrally into tergites and sternites, the two sections being quite different in structure. Some species have rows of a white, waxy secretion on the dorsal surface of the abdomen, or may cover themselves with flocculent wax.
The body rings are frequently studded with elongate-oval or rounded structures, called microtubercles, which may completely cover the body, or occur on the sternites only, or be lacking on some posterior rings. The form, number, and arrangement of microtubercles are useful diagnostic characters.
The abdomen bears a limited number of setae - the lateral seta, the first to third ventral setae, the caudal seta, and the accessory seta. A few species, e.g., Phytoptus avellanae and P. rufensis, also have an anterior subdorsal seta. The relative length of the setae is a valuable specific and generic character, as is the absence of certain setae; for instance, Dacundiopus stylosus n. gen. & sp. lacks a lateral seta, and Asetilobus hodgkinsi n. comb. lacks the second ventral seta. The accessory seta is often absent. The body setae sometimes taper very finely at their distal extremity, making accurate measurement difficult.
GENITALIA. The transverse genital opening is located anteriorly, just behind the hind coxae. Figures 3 and 4 illustrate the female and male genital openings of Aceria tulipae. The easiest means of distinguishing the sex of specimens is the inverted 'V'-shaped nature of the male opening. The female genital opening is covered by a semicircular hinged flap, the coverflap, which may have longitudinal markings or scoring, crescentic scoring, granules, or some other type of ornamentation on its surface. In a few species the coverflap may be devoid of markings. The degree and nature of the coverflap markings are of significance in the generic and specific placement of some species.
A pair of genital setae are always present; their length can be of assistance in species placement.
The internal female genitalia consist of an anterior apodeme behind which are the spermathecal tube and paired, bulb-like spermathecae (Figures 8 and 9). The shape of the apodeme is of considerable significance. The normal type is shown in Figure 8, but in some instances the apodeme is considerably shortened (Figure 9), and may appear as a heavy, transverse black line. Members of the Cecidophyinae have a much shortened apodeme of this type. Phytoptus rufensis has long spermathecal tubes, as compared with the more typical shortened tubes of species of aceria. The nature of the tubes is a useful diagnostic character.
Female internal genitalia have been drawn where possible, but in some species they are difficult to observe, particularly the spermathecae and spermathecal tubes.
LEGS. All eriophyoid mites have only two pairs of legs, divided into coxa, trochanter, patella or genu, tibia, and tarsus (Figure 10). The foreleg and hind leg are essentially similar. In some species there may be a reduction in leg segmentation, or some segments may be fused. Members of the Nothopodinae (Cosella, and Pangacarus n. gen.) lack a distinct tibia, or the tibia and tarsus are fused.
Leg setation is an important character, and it is necessary to be able to clearly locate the respective setae or establish their absence. There are usually three pairs of coxal setae (Figure 6), and from a taxonomic viewpoint the forecoxal or first coxal setae are the most important. Their occurrence, position, and length are all features worth noting. The trochanter lacks setae. The femur usually has a single ventral seta; its absence is of significance. The genu or patella has a single distinctive seta. The foretibia has a single seta, but the hind tibia always lacks it. The tarsi have two long, closely associated setae on the upper surface, and often a short, fine seta arises ventrally, near the distal margin.
The claw and featherclaw arise from the distal part of the tarsus; both are important structures. The rod-like claw may be straight or curved, and often terminates as a knob. The actual and relative length of the claws are of use for species identification. In genus Cosella the foreclaw is unusual in being angled outwards (Figure 146) instead of parallel to the featherclaw. The featherclaw is usually one of two main types. The simple type (Figure 14), which is commonest, has a central stem from which arise branches or rays. The number of rays is an important species character. The second type, less frequently seen, is the divided featherclaw - e.g., in Dacundiopus stylosus (Figure 15) and Diptacus gigantorhynchus (Figure 55) - or some modification of this, as in Brevulacus reticulatus n. gen. & sp. (Figure 16), the featherclaw of which is most unusual. Featherclaw structure is important in genus and species placement.