Table I

Classification of Flea Species Mentioned in the Text

Family Ceratophyllidae

Cemtopbyllus ¿allinae (European chicken flea) C. niger (western chicken flea) Nosopsyllus fasciatus (northern rat flea) Orchopeas howardi Oropsylla montana

Family Ctenophthalmidae

Stenoponia tripectinata

Family Ischnopsyllidae

Myodopsylla insijjnis

Family Leptopsyllidae

Leptopsylla segnis (European mouse flea) Family Pulicidae

Cediopsylla simplex (rabbit flea) Ctenocephalides ccmis (dog flea) C. felts (cat flea)

Echidnophaga gallinacea (sticktight flea)

E. larina

E. myrmecobii

Euhoplopsyllus glacialis

Hoplopsyllus anomalus

Pulex irritans (human flea)

P. simulans

Spilopsyllns cuniculi (European rabbit flea)

Tunga monositus

T. penetrans (chigoe)

Xenopsylla astia

X. bantorum

X. bmsiliensis

X. eheopis (Oriental rat flea)

Family Pygiopsyllidae

Uropsylla tasmanica

Family Vermipsyllidae

Dorcadia ioffi

Vermipsylla alakurt (alakurt flea)

Modified from Lewis, 1993a.

Flea classification is based almost exclusively on the chitinous morphology of cleared adult specimens. Male fleas probably have the most complex genitalia in the animal kingdom, and the morphology of the sclero-tized parts of these organs is important in most systems of flea classification. Although various classification schemes have been proposed for fleas, one that is widely used today is detailed by Lewis (1998). In this classification, the order Siphonaptera is divided into 15 families, the larger of which are the Ceratophyllidae (540 species), Ctenophthalmidae (744 species), Ischnopsyllidae (135 species), Leptopsyllidae (346 species), Pulicidae (207 species), Pygiopsyllidae (185 species), and Rhopalopsyllidae (145 species).

Adult fleas are small (1—8 mm), wingless, almost invariably bilaterally compressed, and heavily chitinized (Fig. 7.1). Many species bear one or more combs, or ctenidia, each appearing as a row of enlarged, sclerotized spines (Figs. 7.1 to 7.3). A comb on the ventral margin of the head is called a genal ctenidium, whereas a comb on the posterior margin of the prothorax is called a pronotal ctenidium. Additional cephalic or abdominal ctenidia occur in some fleas. Smaller rows of specialized setae or bristles adorn various body regions of many fleas. The nature of the ctenidia and specialized setae often reflect the vesti-ture or habits of the host, especially in host-specific fleas. They aid in preventing dislodgement of fleas from the hair or feathers of the host. It also has been suggested that ctenidia may protect flexible joints.

An important sensory feature of adult fleas is the sen-silium (the pygidium of older works), present on abdominal tergum 9 or 10 (Fig. 7.1). This sensory organ aids fleas in detecting air movement, vibrations, and temperature gradients; in some species it also facilitates copulation. It plays an important role in host detection and in initiating escape responses. Just anterior to the sensil-ium in most fleas are the stout, paired antesensilial setae (antepygidial bristles) situated on the posterior margin of tergum 7. Many adult fleas, especially those of diurnal hosts, possess well-developed eyes (Fig. 7.3), which are actually clusters of ocelli. Eyes are well developed in most adult fleas of medical or veterinary importance (Figs. 7.2 and 7.3). Short, clubbed, three-segmented antennae are held inside protective grooves called antennal fossae on the sides of the head which prevent antennal damage as the flea moves through the pelage of its host.

The mouthparts of adult fleas are well adapted for piercing and sucking (Figs. 7.3 and 7.4). After a suitable feeding site has been located by the sensory labial palps, three

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