Jritosternum

r"EPNAL PLATE fTflirREWE HE"AS~:lRNAL PLATE

.GENITAL-VENTRAL pi i<Tr METAPODAL PLATE

ANAL PLATt

FIGURE 23.1 Generalized morphology of adult female mite (Mesostigmata, Laelapidae, Androlaelups fabrenholzi), ventral view. (From Baker tt at., 1956.)

mouthparts consist primarily of a pair of chelicerae, each of which is typically three-segmented and terminates in a chela, or pincer. The chela is composed of a fixed digit and a movable digit designed for seizing or grasping- In the case of certain parasitic mites the chelicerae are highly modified as long, slender structures for piercing skin to feed on blood and other host tissues. In some groups, structures associated with the mouthparts may be modified as attachment devices to help secure them to their hosts (e.g., chiggers).

The idiosoma can be divided into several regions. The anterior part bearing the legs is the podosoma. The posterior section behind the legs is the opisthosoma. Other regions include the propodosoma, that portion of the idiosoma bearing the first and second pairs of legs, and the hysterosoma, extending from just behind the second pair of legs to the posterior end of the body. The designation of these body regions is helpful to morphoiogists and taxonomists in locating specific setae and other structures. The size and arrangement of sclerotized plates, the chaetotaxy, and the nature and location of sensory structures on the idiosoma serve as important taxonomic characters.

Mites typically have four pairs of legs as nymphs and adults, but they have only three pairs as larvae. The legs are divided into the following segments: coxa, trochanter, femur; genu, tibia, tarsus, and pretarsus. The pretarsus commonly bears a pair of claws, a single median em-podium, and, in certain groups, a membranous pulvil-lus. These structures are highly variable among different groups of mites and aid in movement or in clinging to various surfaces, including hosts.

The respiratory systems of mites often include tracheal ducts which supplement the exchange of oxygen, carbon dioxide, and other gases across the body surface. The presence of spiracular openings associated with the tracheal ducts, commonly denoted by a sclerotized plate, or stigma (plural stigmata), and their location on the body provide important taxonomic characters for recognizing the acariñe suborders. In the Prostigmata, for example, the stigmata are located at the anterior margin of the idiosoma. In the Mesostigmata they are usually located dorsolateral^ to the third or fourth pairs of legs, whereas in the Oribatida (Cryptostigmata) they are typically hidden, opening ventrolaterally near the bases of the second and third pairs of legs. Tracheal systems and spiracular openings are lacking in the Astigmata.

Reproductive structures are very diverse among mites, providing important characters for distinguishing the sexes and identifying taxa. Sperm transfer may be direct (e.g., insemination by transfer of sperm via the male aedeagus to the sperm storage organ, or spermatheca, of the female) or indirect (e.g., transfer of sperm via the male chelicerae to the female genital opening).

A few points should be mentioned regarding the internal morphology of mites that are pertinent to species of medical-veterinary importance. The digestive system handles primarily liquefied food that has been preorally digested by enzymes secreted in the saliva, The paired salivaryglands are typically located in the anterior portion of the idiosoma and open via ducts into the mouth region of the gnathosoma. In addition to digestive enzymes, these glands secrete anticoagulants in hematophagous mites. In certain groups (e.g., chiggers) they may produce cementing substances to help anchor the mouthparts in host skin. Also important in certain acariñe groups are coxal glands. They are derived from excretory structures and serve primarily in osmoregulation. Waste products, in the form of guanine, are excreted by one or two pairs of long, slender Malpighian tubules that open into the alimentary tract just anterior to the hindgut.

Allergy Relief

Allergy Relief

Have you ever wondered how to fight allergies? Here are some useful information on allergies and how to relief its effects. This is the most comprehensive report on allergy relief you will ever read.

Get My Free Ebook


Post a comment