Fleas Taxonomy & Phylogeny  

Zoological Institute

Taxonomy of Siphonaptera

A classification of siphonapteran families and scheme of their phylogenetic relationships are proposed (Medvedev, 1994, 1998) on the basis of features of 50 structures of head, thorax, and abdomen. Four family complexes of evolutionary trends may be distinguished: they are infraorders Pulicomorpha, Pygiopsyllomorpha, Hystrichopsyllomorpha, and Ceratophyllomorpha.

One other classification of the order Siphonaptera was recently published (Smit, 1982). In the classification of Smit, the order is divided into five superfamilies: Hystrichopsylloidea, Ceratopsylloidea, Malacopsylloidea, and Pilicoidea.

Our classification of siphonapteran families see below or use interactive systematic tree.

Information about concrete taxa see in interactive database.

         Ordo: SIPHONAPTERA  Latreille, 1825
                = APHANIPTERA  Kirby et Spence, 1816
                = APHANIPTERES  Acloque, 1897
                = APTERA  Linnaeus, 1758
                = MEDAMOPTERA  Leach, 1815
                = PSYLLOMORPHA  Eysell, 1913
                = PULICARII  Rondani, 1841
                = PULICIDAE  Stephens, 1829
                = PULICIDES  Billberg, 1820
                = PULICINA  Burmeister, 1829
                = PULICITES  Newman, 1834
                = ROPHOTEIRA  Schellenberg-Clairville, 1798
                = SIPHONAPTEROS  Gonsalves, 1912
                = SUCEURS  Latreille, 1795
                = SUCTORIA  De Geer, 1778
                = SUCTORIDEA  Walker, 1851
            Infraordo: PULICOMORPHA  Medvedev, 1998
               Superfamilia: PULICOIDEA  Billberg, 1820
                  Familia: Pulicidae  Billberg, 1820
                            = Archaeopsyllidae  Oudemans, 1909
                            = Sarcopsyllidae (partim)  Taschenberg, 1880
                            = Xenopsyllidae  Glinkiewickz, 1907
                  Familia: Tungidae  Taschenberg, 1880
                            = Dermatophilidae  Oudemans, 1906
                            = Echidnophagidae (partim)  Oudemans, 1909
                            = Hectoropsyllidae  Oudemans, 1906
                            = Rhynchoprionidae  Baker, 1905
                            = Sarcopsyllidae (partim)  Taschenberg, 1880
               Superfamilia: MALACOPSYLLOIDEA  Baker, 1905
                  Familia: Malacopsyllidae  Baker, 1905
                            = Megapsyllidae  Baker, 1898
                  Familia: Rhopalopsyllidae  Oudemans, 1909
               Superfamilia: VERMIPSYLLOIDEA  Wagner, 1889
                  Familia: Vermipsyllidae  Wagner, 1889
                            = Pulicidae (partim)  Taschenberg, 1880
               Superfamilia: COPTOPSYLLOIDEA  Wagner, 1928
                  Familia: Coptopsyllidae  Wagner, 1928
               Superfamilia: ANCISTROPSYLLOIDEA  Toumanoff et Fuller, 1947
                  Familia: Ancistropsyllidae  Toumanoff et Fuller, 1947
            Infraordo: PYGIOPSYLLOMORPHA  Medvedev, 1998
               Superfamilia: PYGIOSYLLOIDEA  Wagner, 1939
                  Familia: Lycopsyllidae  Baker, 1905
                  Familia: Pygiopsyllidae  Wagner, 1939
                  Familia: Stivaliidae  Mardon, 1978
            Infraordo: HYSTRICHOPSYLLOMORPHA  Medvedev, 1998
               Superfamilia: HYSTRICHOPSYLLOIDEA  Tiraboschi, 1904
                  Familia: Hystrichopsyllidae  Tiraboschi, 1904
                            = Ctenopsyllidae  Baker, 1905
                            = Neopsyllidae  Oudemans, 1909
                            = Pulicidae (partim)
                            = Typhlopsyllinae (partim)
                  Familia: Chimaeropsyllidae  Ewing et I.Fox, 1943
               Superfamilia: MACROPSYLLOIDEA  Oudemans, 1909
                  Familia: Macropsyllidae  Oudemans, 1909
               Superfamilia: STEPHANOCIRCIDOIDEA  Wagner, 1928
                  Familia: Stephanocircidae  Wagner, 1928
            Infraordo: CERATOPHYLLOMORPHA  Medvedev, 1998
               Superfamilia: CERATOPHYLLOIDEA  Dampf, 1908
                  Familia: Ceratophyllidae  Dampf, 1908
                  Familia: Leptopsyllidae  Rothschild et Jordan, 1915
                  Familia: Ischnopsyllidae  Wahlgren, 1907
                            = Ceratopsyllidae  Baker, 1905
                            = Ceratosylliclae  Jordan et Rothschild, 1906
                            = Nychopsyllidae  Eysell, 1913
                            = Nycteridiphilidae  Dalla Torre, 1914
                            = Pulicidae (partim)
                            = Typhloceratidae  Oudemans, 1909
                            = Typhlopsyllinae (partim)
                  Familia: Xiphiopsyllidae  Wagner, 1939

Phylogeny of Siphonaptera

                       ===================== Pulicoidea
                       |                 === Malacopsylloidea
     ===Pulicomorpha===|              ===|
     |                 |  ============|  === Vermipsylloidea
     |                 |  |           |
     |                 ===|           ====== Coptopsylloidea
     |                    |
     |                    ================== Ancistropsylloidea
     |     ===Pygiopsyllomorpha============= Pygiopsylloidea
     |     |
     |  ===|                             === Hystrichopsylloidea
     |  |  |                          ===|
     |  |  ===Hystrichopsyllomorpha===|  === Macropsylloidea
     ===|                             |
        |                             ====== Stephanocircidoidea
        ===Ceratophyllomorpha=============== Ceratophylloidea
Tree of fleas (Siphonaptera) infraorders and superfamilies by Medvedev (1994, 1998).

Table of Contents

Characteristics of Siphonaptera
The Infraorders of Siphonaptera
Discussion of Phylogenetic Relationships
Recent Problems of Flea Systematics


The Siphonaptera, or fleas, are one of the major groups of blood-sucking insects. They belong to holometabolic insects, as like as Diptera, Lepidoptera, etc. Fleas form a separate well-differentiated order, although phylogenetically they are regarded to be closer to Diptera and Mecoptera. At present approximately 2000 species and subspecies of fleas are known. Adult fleas are obligatory hematophages parasitising warm-blooded animals (mammals and birds). Wormlike free-living legless flea larva develops in the litter of host's nest. The majority of fleas are periodically attacking burrow or nest- dwelling parasites, capable have long time to present in host's fur, unlike free blood-suckers, such as, for example, Diptera or some bugs.

Fleas are secondarily wingless insects. Their body is flattened on the sides and is represented by 3 major parts, or tagma: head, thorax, abdomen. Thorax of fleas is provided with three pairs of legs, the hind legs are the longest. The shape of the head, the flat body shapes and prehensile claws of legs help it to move easily through host's wool. Length of jump some flea species attains 32 cm, average body length being from 1 to 5 mm. Colour of flea body may be light yellow, yellowish black, brown black or jet-black.

Fleas are widely spread on all continents, Antarctica included. They occur on hosts and in their nests in all types of habitats from the equatorial deserts and tropical rainforests to the northernmost regions of Arctic tundra. In general in Eurasia as in other continents the largest number of species and genera of fleas occur in several regions with temperate subtropical climate and predominance of mountain landscapes. The most numerous flea fauna is known for Eurasia.

Representatives of the order are known as vectors of plague microbes, murine typhus rickettsiae and some other pathogens. The great practical significance of fleas determines the necessity to study their fauna for the entire world and separate regions and to elaborate of systematics of the order. Epidemiological significance of fleas determined the great interest of specialists from different countries of the world.

The world fauna of this relatively small insect order had been mainly studied by the 1970s-1980s. However classification and phylogeny of the order has not been elaborated completely. No extensive reviews on the fauna of the former Soviet Union and the USA have been published yet. The elaboration of the natural system of the order, however, is complicated because all fleas are highly specialised parasites. Only a few specimens of fossil fleas from Eocene Baltic and Miocene Dominican amber are currently known. In their characteristics they are nearly identical to the recent forms. The existed classifications of the fleas are based on characters taken separately, without the analysis of their evolutionary relationships.

Characteristics of Siphonaptera

The most distinctive feature of fleas is flattened wingless body with legs armed by long claws. The third pair of the legs is the longest. They are the principal jumping organs.

Other derived characteristics of fleas are:

The head capsule of fleas is very modified. It is lucked real suture dividing head on front, clypeus and etc. It is high, narrow and cuneate.

The propleurosternum of thorax covers the head from below to the peristomal aperture, as result of which it is immobile.

There is one mobile conjunction between closely connected head and prothorax on the one hand and meso- and metathorax on the other hand.

The antennae of fleas usually are in antennal fossae. The antennal fossa divides the head into anterior and posterior parts.

The ovate abdomen of the adult flea includes 10 segments. The genital apparatus of male fleas consists of the aedeagus, modified tergites and sternites of the 8th and 9th abdominal segments and claspers. The aedeagus and claspers (after R.Snodgrass) derive from primary phallic lobe. The modified tergites and sternites of fleas belong to abdominal segments 7-9.

The Infraorders of Siphonaptera

1. Infraorder PULICOMORPHA S.G. Medvedev, 1998

This infraorder includes 5 superfamilies: Pulicoidea Billberg, 1820 (Pulicidae and Tungidae Taschenberg, 1880), Malacopsylloidea Baker, 1905 (Malacopsyllidae and Rhopalopsyllidae Oudemans, 1909), Vermipsylloidea Wagner, 1889 (Vermipsyllidae), Coptopsylloidea Wagner, 1928 (Coptopsyllidae), and Ancistropsylloidea Toumanoff et Fuller, 1947 (Ancistropsyllidae).

1.1. Morphological characteristics of the Pulicomorpha

In general, the infraorder Pulicomorpha shows a trend toward a more compact body, achieved by both its shortening and the increasing height of thoracic segments. For example, the mesonotum of fleas of the families Tungidae, Pulicidae, Malacopsyllidae, Ancistropsyllidae, Vermipsyllidae, and the subfamily Rhopalopsyllinae is as high as wide or even higher, whereas in other families, the notum is longer than high. This trend probably resulted in a number of structural features of the thorax and entire body of these fleas, listed below.

The additional features of Pulicomorpha are the next. The external interantennal groove on the head is obsolete or absent; the internal ridge, however, is present. The single mesopleural rod is attached to the anterodorsal angle of the thorax mesopleuron. Its apex sometimes bears a thin accessory process, which is connected to the mesonotum. The pronotum has entire, rather than divided, ventral margin. The anterior arm of the 1st thoracic link-plate, the outer lobe of the 2nd thoracic link-plate, and the metathoracic squamulum are absent. Representatives of most families comprising the infraorder Pulicomorpha lack pronotal ctenidia; instead, the pronotal collar is well developed, so that its posterior margin overlies the mesothorax dorsally. The metanotum and abdominal tergites bear no spinelets (except in the subfamily Rhopalopsyllinae and family Ancistropsyllidae). In males, abdominal segment VIII has a small tergite and, contrariwise, a large sternite, often bearing lobes on its posterior margin. Sternite IX of males usually has straight proximal arm and weakly modified distal ones. Tergite IX of females can be present or reduced.

1.2. Host-association and distribution of the Pulicomorpha.

The infraorder Pulicomorpha differs from other 3 infraorders in that its representatives are associated with such different mammal groups as Carnivora, Dasypodidae, Pholidota, Hyracoidea, and Artiodactyla. Among rodents, this infraorder is characteristically closely associated with Cricetidae and Muridae. Lagomorpha are the third group with respect to the number of host species. Different families within the infraorder display a trend toward "fixed" or semi-fixed" parasitism.

Within the infraorder Pulicomorpha, relations between faunas of Africa and Asia and between those of Africa and S America can be revealed. The ancestral group of the Pulicomorpha is likely to have occurred in Africa.

1.3. Families of the Pulicomorpha and their distribution

Fleas of the monotypic family Coptopsyllidae appear to be the closest to the stem form of the pulicoid complex; they are distributed in Western and Middle Asia, living on gerbils. Coptopsylla wasiliewi, the only S African species of this genus, has an upward-directed frontal tubercle similar to those observed in the S American family Rhopalopsyllidae. Other Coptopsylla species have deep groove originating at this tubercle and running parallel to the ventral margin of the head, which are sometimes mistaken for the frontoclypeal boundary. The apex of the fold process is characteristically directed dorsally, like the frontal tubercles in fleas of the infraorder Pulicomorpha. Fleas of the family Coptopsyllidae are additionally characterised by some generalised features of their head and thorax, which probably represent the primitive state for the infraorder Pulicomorpha.

The ancestral taxa of Vermipsyllidae and Ancistropsyllidae migrated from Africa into Asia via Europe; fleas of the former family parasitize carnivores, and those of the latter live on chevrotains. The family Pulicidae became the most widely distributed in Africa; its host spectrum includes various groups: Hyracoidea, Pedetidae, Rodentia, Lagomorpha, Phacochoerus, and Carnivora. Later, fleas of the genera Echidnophaga and Xenopsylla migrated to Asia, the former spreading as far as Australia. In Australia, 10 endemic Echidnophaga species live on echidnas, marsupials, and rodents. Species of the genus Nesolagobius, described from recently extinct Sumatran hares, appeared during the migration of Pulicidae fleas from Africa to SE Asia. The distribution of the family Tungidae indicates the relations between the flea faunas of Africa and S America. The genus Neotunga occurs in Africa, with its species living on Pholidota, whereas the other 2 genera, Hectopsylla and Rhynchopsyllus, are found in S America. The genus Tunga has a remarkable distribution, its species being represented in S and N Americas, Japan, and China.

The S American families Rhopalopsyllidae and Malacopsyllidae have a number of characters resembling those of Pulicidae and Tungidae. The ancestors of these 2 families must have migrated from Africa to S America on caviomorph rodents. This is indicated by the fact that the distribution of the family Rhopalopsyllidae is largely restricted to the distribution area of Caviomorpha, even though these fleas parasitize a broad spectrum of S American mammals.

2.Common characters of the infraorders Pygiopsyllomorpha, Hystrichopsyllomorpha, and Ceratophyllomorpha

2.1. Morphological characteristics of the infraorders

Representatives of these 3 infraorders have elongate body, with all thoracic segments longer than high. The elongate body is flexible owing to the non- rigid junction between pro- and mesothorax. The intersegmental membranes are protected on the outside by denticles of the pronotal ctenidia, which are absent only in separate genera of these infraorders, whose species live on various hosts.

The intercervical part of the postgenal bridge is typically not developed in representatives of the infraorders Ceratophyllomorpha, Pygiopsyllomorpha and Hystrichopsyllomorpha. Instead, the development of the postgenal bridge is related either to forward dilation of the initially narrow rod, or to formation of the intergenal process, located between the inner margins of genae (Medvedev, 1989). The tentorial arms attach to the gena; their anterior, middle, and posterior parts are sometimes reduced. The occipital apodeme is present.

Fleas of these infraorders have 2 distinct arms of the mesopleural rod, which attaches to the notum and pleuron caudally to their anterior margins. The dorsal margin of the mesopleuron has a backward slant, and the lower margin of the notum lies below the anterodorsal angle of the pleuron. The outer lobe of the 2nd link-plate and the well-developed anterior arm of the 1st link-plate are present. The mesosternite in its primitive state has a spoon-shaped base with the well-developed anterior wall. These infraorders have a common way of reinforcement of meso- and metasternites, consisting in formation of a carinate wall. Fleas of these infraorders possess a squamulum (except in the family Xiphiopsyllidae); the ventral margin of the pronotum is divided into 2 lobes, the hind lobe sometimes being secondarily reduced. The apodeme of the prothorax is wide, while that of the mesothorax has a dilated apex and well- developed ventral processes.

In fleas belonging to these infraorders, the apodeme of tergite IX is arc- shaped or visor-shaped, protruding posteriad. The manubrium of the main part of the clasper has a narrow canal running along its ventral margin. Fleas of this group are characterised by the presence of the pronotal ctenidia and spinelets on abdominal tergites.

2.2. Distribution of the infraorders

The taxa belonging to these infraorders had distributed via the Antarctic Bridge in the S hemisphere and the Beringian Bridge in the N hemisphere. These groups show characteristic links between the faunas of S America and Australia and between those of S America and Palaearctic. Fleas of the infraorders Ceratophyllomorpha, Pygiopsyllomorpha and Hystrichopsyllomorpha are typically closely associated with Rodentia, Chiroptera, Insectivora, Macroscelidae, and partly also Lagomorpha.

3. Common characters of the infraorders Pygiopsyllomorpha and Hystrichopsyllomorpha

The characters shared by these infraorders are largely results of parallel evolution. The synapomorphies of these 2 groups are probably the absence of spinelets on the metanotum (except in Chimaeropsyllidae); the genal bridge and intergenal process; the arcshaped apodeme, often separated from tergite IX by a ridge; and the hypotendon attaching to the sclerotized ventral wall of the aedeagus.

Such features as similar mesosternites with thickened base, the antennal fossa closed by the collar of the ventral head margin, and a number of other characters, have appeared independently in these family groups. In fleas belonging to the infraorders Hystrichopsyllomorpha and Pygiopsyllomorpha, the spinelets are sometimes present on tergites I-V, being located on the straight margin of the metanotum and abdominal tergites.

Both infraorders, which must have separated early in their evolution, have some unique features; this is especially true for the former.

4. Infraorder PYGIOPSYLLOMORPHA S.G. Medvedev, 1998

This infraorder includes 3 families, appropriately united in a single superfamily Pygiopsylloidea (Lycopsyllidae Baker, 1905; Pygiopsyllidae, Stivaliidae Mardon, 1978).

4.1. Morphological characteristics of the infraorder Pygiopsyllomorpha

The head capsule has the intergenal process, from which the bridge is formed. A shallow exterior interantennal suture is present. The frontal tubercle and genal ctenidia are absent (except in the genus Hoogstraalia). Two pairs of campaniform sensilla are present. The antennal fossae merge with their inner walls; the genal lobes are often flattened.

The upper margin of the propleurosternum lacks an incision corresponding to the cervical link-plate; 3rd thoracic link plate is present. Both sexes lack the antennal fossae on the pleurosternum. The crochets of the aedeagus are reduced and replaced by peculiar apical sclerites operated by a pair of muscles. The Y-sclerite has additional basal lobes. The satellite sclerite is often shifted into the inner tube cavity, or reduced.

The articulations between sternite IX and the aedeagus, if present, are formed either by the modified ventral margin of the cover, or by special processes of the inner tube. The movable process in these fleas has a shortened main part; its inner wall forms transverse bridges. The movable process is elongate, with its base shifted toward the base of the main part; the articulatory condyles of the digitoid are obsolete. Abdominal tergite VIII of males is small.

The peculiar feature of the infraorder Pygiopsyllomorpha is the absence of spinelets not only on the metanotum, but also on abdominal tergite 1.

4.2. Families of the infraorder Pygiopsyllomorpha

According to the generally accepted classification, all genera of pygiopsylloid fleas are united in a single family Pygiopsyllidae. In our opinion, 3 separate families should be distinguished within the infraorder Pygiopsyllomorpha. The first family, Lycopsyllidae, clearly differs from the other 2 families, Pygiopsyllidae and Stivaliidae, in structural peculiarities of the genal lobe (resembling those of pulicoid fleas), simple interantennal wall, reduced tentorial arms in the middle, single mesopleural rod and the shape of the mesosternal apodeme with its wide base. Fleas of the genera Choristopsylla, Lycopsylla, and Uropsylla are characterised by reduction of the hypotendon (in Uropsylla also endotendons) and the absence of apical sclerites, with the muscle tendons attaching to the wall of the terminal chamber.

The family Stivaliidae is characterised by diverse variants of articulation between sternite IX and the aedeagus, and also by strongly developed basal arm of the Y-sclerite. The family Pygiopsyllidae lacks the specialised features typical of Stivaliidae, differing from the latter in the mode of articulation between the digitoid and the main part of the clasper.

4.3. Host-association and distribution of the Pygiopsyllomorpha

A particular feature of this infraorder is that its distribution is associated with the Indo-Malayan Region, where 26 of 37 its genera and 62% its species occur. Most of these genera (22) belong to the family Stivaliidae, the majority of endemic genera (13) occurring in the Papuan Subregion, in particular on New Guinea. A number of representatives of Stivaliidae (109 species in 23 genera) occur in SE Asia and Africa, living on Muridae and tree-shrews. The family Pygiopsyllidae (48 species in 10 genera) is more extensively represented in Australia (7 of the 10 known genera), and also in New Zealand (4 genera). Fleas of the family Lycopsyllidae (8 species in 4 genera) parasitize echidnas, wombats, and predacious marsupials.

On the total, different species of the infraorder have been found on marsupial hosts belonging to 67 genera (of 74 known) and 9 families, the main host families being Dasyuridae and Peramelidae. However, fleas of the infraorder Pygiopsyllomorpha are as extensively represented on rodent hosts of 36 genera, among which Muridae are the prevailing group. Fleas belonging to most genera of the infraorder occur on both Muridae and Marsupialia, only few species being strictly specific parasites of Marsupialia. An example of the latter group is fleas of the genus Lycopsylla, living on wombats.

4.4. Hypotheses concerning the origin of the infraorder

Three hypotheses concerning the origin of the infraorder Pygiopsyllomorpha may be put forward, considering the place of origin of this group to be, respectively, America, Australia, and Asia. It should be noted in this connection that the infraorder includes only one genus Ctenidiosomus (Pygiopsyllidae), possessing the common lateral crochets, whereas other representatives of the infraorder have apical sclerites. Species of this genus are distributed exclusively in S America.

5. Infraorder HYSTRICHOPSYLLOMORPHA S.G. Medvedev, 1998

The infraorder includes 3 superfamilies: Hystrichopsylloidea (Hystrichopsyllidae, Chimaeropsyllidae Ewing et I. Fox, 1943), Macropsylloidea Oudemans, 1909 (Macropsyllidae) and Stephanocircoidea Wagner, 1928 (Stephanocircidae).

5.1. Morphological characteristics of the infraorder Hystrichopsyllomorpha

Even though there are no apomorphic characters shared by all representatives of the infraorder, its families possess a number of characters, which have evolved independently but on the common basis. A possible explanation of this fact is that the infraorder Hystrichopsyllomorpha includes several most ancient flea taxa, the intermediate forms between which have become extinct.

The intergenal process, giving rise to the postgenal bridge, has been observed in a number of representatives of - Hystrichopsyllomorpha. Fleas of this infraorder, with exception of several genera, have no sex dimorphism with respect to the interantennal wall. The frontal tubercle varies in structure from simple tubercle to fold-shaped and joint tubercle. The prefrontal ridges are distinct; the tentorial arms are reduced posteriorly or anteriorly. The apex of the genal lobe protrudes ventro-posteriad. The antennal fossa is either open or closed by a collar of the ventral head margin.

The antennal fossae of the propleurosternum are sometimes absent or, if present, distinct in both sexes; its upper margin is smooth. The mesosternite has a wide or spoon-shaped base, abruptly narrowing anteriad, and no auxiliary arms between the sternite and pleura. The mesosternite base may be also carinate, in which case its ventral margin is positioned at the same level as that of the mesopleuron. The sclerotized area of 2nd thoracic link-plate is mostly horseshoe-shaped. The frame of the aedeagus is variable, including almost all the structural types found in other infraorders as well. The articulation between the aedeagus and sternite IX is usually absent, and sometimes formed by modification of the ventral margin of the cover. The apodeme of tergite IX is arc-shaped or (less frequently) triangular, separated by a ridge. The clasper has no acetabular process.

5.2. Host-association and distribution of the Hystrichopsyllomorpha

The infraorder Hystrichopsyllomorpha is associated with rodent hosts belonging to Cricetidae and Muridae; however, the third largest host group for these fleas are insectivores (Soricidae and Talpidae). This infraorder probably originated in Asia, where from its representatives migrated into S America via N America. Later, its distribution was affected also by the intercontinental connections between America and Australia, which is illustrated by the distribution pattern of such peculiar families as Macropsyllidae and Stephanocircidae.

5.3. Families of the infraorder Hystrichopsyllomorpha

The Australian family Macropsyllidae (2 species in 2 genera) appears to represent a relic part of the vast ancient S American-Australian fauna associated with marsupials. Fleas of this family have been collected on rats and various marsupials.

The family Stephanocircidae (51 species in 9 genera) is characterised by the specific structure of head having a separate frontal part ("helmet") and the aedeagus with a peculiar thin apodeme and a membranous cover. However, fleas of this family resemble other representatives of the hystrichopsylloid complex in the thoracic morphology. The family Stephanocircidae is divided into 2 subfamilies, each is having distinct morphological peculiarities of the head, thorax, and aedeagus. The subfamily Stephanocircinae is distributed in Australia and associated with various marsupials and rats. The subfamily Craneopsyllinae is represented in S America, where its species parasitize hamsters living in the alpine zone of the Andes. The structural features of these fleas reflect their biology, i.e., adaptation to rapid movement in the host fur. Fleas of the family Stephanocircidae may have been initially associated with S American marsupials, which have largely become extinct. The parasitism on marsupials, having no nests, led to the morphological adaptations resembling those of Ischnopsyllidae fleas, which live on chiropteran hosts.

It is probable that the family Stephanocircidae was formed during the same period when ancestors of the subfamily Doratopsyllinae (Hystrichopsyllidae) migrated into S America.

The family Hystrichopsyllidae is the largest in this complex (567 species in 45 genera). Some authors divide it into several separate families, e.g., a small family Hystrichopsyllidae (including Macropsyllidae) and a vast family Ctenophthalmidae (Smit, 1982). An important factor in the evolution of this family was its association with Cricetidae, which migrated along mountain systems. Species of the family Hystrichopsyllidae appear to have spread from foothill areas to plain forests and also to semi-deserts and deserts of the Turan-Persian Subregion. Representatives of this family are characteristically absent in deserts of the Sahara-Arabian and Caspian Subregions. Most subfamilies of the family Hystrichopsyllidae must have been of Holarctic origin. Their migration from Asia into N America may have occurred via the N Atlantic and Beringian Bridges. The subfamilies associated with Cricetidae probably used the Beringian Bridge; they also migrated into Africa via Europe with their hosts. The migration of species of this family from N America to S America probably occurred twice: in late Cretaceous and Miocene.

The family Chimaeropsyllidae is endemic to the Afro-Tropical Region, being almost 'exclusively represented in the Kappian Subregion. The position of this family within the infraorder Hystrichopsyllomorpha is similar to that of the family Xiphiopsyllidae within Ceratophyllomorpha. The genus Chiastopsylla is the least specialised within Chimaeropsyllidae; its 16 species live on mice and rats. The genera with more specialised morphological features of the head and thorax has hosts belonging both to Muridae and to the Afrotropical order Macroscelidea, known since Eocene-Miocene. It is possible that fleas of this family, originally associated with Muridae, have adapted to parasitism on Macroscelidea under the arid conditions of the Kappian Subregion.

6. Infraorder CERATOPHYLLOMORPHA S.G. Medvedev, 1998

The infraorder is represented by a single superfamily Ceratophylloidea (Ceratophyllidae Dampf, 1908; Leptopsyllidae Rothschild, 1915; Xiphiopsyllidae Wagner, 1939; Ischnopsyllidae Wahlgren, 1907).

6.1. Morphological characteristics of the infraorder Ceratophyllomorpha

The intergenal process has not been found. Instead, a wide bridge is present, with the cervical membrane attaching to its posterior margin. As the primitive state, fleas of this infraorder probably had either a simple interantennal wall, or an interantennal ridge with external groove. In the family Ischnopsyllidae, the groove is transformed into the interantennal furrow, whereas a simple wall is present in Xiphiopsyllidae. In Ceratophyllidae and Leptopsyllidae, the structure of the interantennal wall is subject to sex dimorphism, being present in the form of a suture in males and a simple wall in females. Finally, in fleas of the subfamily Leptopsyllinae, the interantennal furrow is formed. The structure of the frontal tubercle varies according to one of the following sequences: (1) simple tubercle - complex prominent tubercle - insunk prominent tubercle, or (2) simple prominent tubercle - deciduous tubercle without a fossa below its base (Ischnopsyllidae).

The structure of the antennal fossae also subject to sex dimorphism: the fossa continues to the propleurosternum as a groove in males and as a narrow slit in females. Within this complex of families, the closed antennal fossa is formed owing to downward expansion of the postero-ventral angle of the head and backward expansion of the genal lobe.

The meso- and metasternites are spoon-shaped or modified carinate. The mesothoracic apodemes never form a wide base in fleas of this infraorder. The arms of the mesopleural rod (initially close together in most genera) are separated, the second arm being attached to the dorsal angle of the pleuron. The mesonotum often bears distinct lateral ridges. The metasternal "furca- saddle" has a wide median plate and small or triangular dorsal processes. The stigma of the metepimere varies in shape from broad-rounded (with a trend towards reduction of its inner structures) to reniform or oviform. The sclerotized area of the 2nd thoracic opiate is semi-closed, triangular. The aedeagus has a shortened apex (the aedeagal apodeme is 2.3-2.5 times as long as the apex) and well-developed crochets, which often have a complicated three-dimensional arrangement. The crochets are operated by a single pair of muscles and form various and complicated articulations with the distal arms of abdominal sternite IX. This peculiarity has probably led to reinforcement of the attachment site for the muscles running from the lateral apodeme plates to the hypotendon; as a result, the latter has become sclerotized and attached to sternite IX. The flexibility of the aedeagus frame is ensured by deep fossae forming on its apodeme anteriorly to the fulcrum base. Fleas of the families Leptopsyllidae and Ischnopsyllidae have strongly elongate neck of the aedeagus. These 2 families are characterised by connections between the fulcrum and lateral walls of the cover; in the former, this feature is almost synapomorphic, whereas in the latter, it is observed in representatives of 2 tribes only. The satellite sclerite is separate.

Fleas of the families Ceratophyllidae, Leptopsyllidae, and Xiphiopsyllidae have denticles on abdominal tergites I-IV. Shallow incisions are present at denticles bases (except genera Peromyscopsylla and Sigmactenus (Leptopsyllidae)).

The clasper has a partly sclerotized inner wall, whose dorsal margin forms a ridge separating the tlaw from the apodeme of abdominal tergite IX, which is characteristically triangular. Tergite VIII of males is low and sometimes bears lateral lobes. The hypotendon is connected with sternite IX, whose distal arms are divided in 3 parts and forms an articulation with the aedeagal crochets. Tergite VIII of males is strongly developed; tergite IX of females is completely reduced.

6.2. Host-association and distribution of the Ceratophyllomorpha

The infraorder most probably originated in Asia, where the majority of its taxa occur. The distribution of most taxa of this infraorder had been affected by the Beringian Bridge. The major host group of the infraorder Ceratophyllomorpha is Cricetidae, the less important host taxa being Sciuridae, Chiroptera, and Ochotonidae (Lagomorpha).

6.3. Families of the infraorder

The family Ceratophyllidae (397 species in 44 genera) has a distinct Asian- American distribution, formed owing to the Beringian bridge. The majority of species occur in the Palaearctic and Nearctic faunas (49 and 30% of the total species number, respectively). The Neotropical Region has 11% of species, Indo-Malayan Region, 7%, and Afro-Tropical Region, 4%. Representatives of this family are absent in New Guinea and Australia but present in New Zealand. According to Traub et al. (1983), the family Ceratophyllidae appeared in Early Oligocene (38-40 million years ago) on S American Sciuridae and secondarily adapted to parasitism on Cricetidae, other rodent groups, and birds. Representatives of this family are absent on such ancient host groups as Marsupialia, Insectivora, Spalacidae, etc., which, in our opinion, suggests that this family is phylogenetically young.

The family Xiphiopsyllidae comprises a single genus Xiphiopsylla with 8 species, occurring on Muridae in E Africa. The peculiar feature of these fleas is the specific, uniformly thickened setae on the thorax and abdomen. In general, however, fleas of this family resemble members of the family Ceratophyllidae.

The family Leptopsyllidae comprises 30 genera and 235 species, 87% of which (i.e., 205 species in 26 genera) occur in Palaearctic. The Nearctic Region has 17 species in 7 genera; the faunas of both AfroTropical and Indo-Malayan Regions include 10 species in 3-4 genera. The family Leptopsyllidae must have originated in Asia and migrated into N America on aplodontid hosts, possibly in Eocene. Species of Odontopsyllus, living on Lagomorpha, may have migrated from N America into Europe via the N Atlantic pathway. Later, fleas of the genera Aconothobius, Ctenophyllus, Geusibia, Amphipsylla, and Peromyscopsylla probably migrated into N America via the Beringian Bridge, on Cricetidae and Muridae. This family appears to have been initially associated, besides Aplodontidae, also with Ctenodactylidae and Dipodidae, which have existed since Early Eocene. The subsequent distribution of the family Leptopsyllidae resulted from their coevolution with Cricetidae (which appeared early in Oligocene) and later with Muridae (since Pleistocene).

Fleas of the family Ischnopsyllidae (122 species in 20 genera) are parasites of Chiroptera. The family is divided into 2 subfamilies: the monotypic subfamily Thaumapsyllinae, including parasites of Megachiroptera in the New World tropical area; and Ischnopsyllinae, consisting of 19 genera, whose representatives live on bats.

It may be assumed that the family Ischnopsyllidae appeared late in Eocene simultaneously with its recent hosts: bats of the families Vespertilionidae and Molossidae. The family migrated from Eurasia into Africa and (via Australia and Antarctica) S America. The ancestors of S American genera united into the tribe Sternopsyllini probably entered S America via Antarctica on bats of the genus Tadarida. Species of Sternopsyllini live not only on bats of this genus, but also related genera endemic to S America. In the Old World, fleas of the family Ischnopsyllidae had become broadly distributed on Vespertilionidae in the Palaearctic temperate zone, and on Molossidae in the Afro-Tropical and Indo-Malayan Regions. The migration of species of the genus Nycteridopsylla from Asia into N America probably occurred later, via Beringia.

Discussion of Phylogenetic Relationships

Various taxa of fleas are established using numerous characters which often show parallel trends of development on a homologous basis. This fact impedes the development of classification of this group, because their structures are often very similar, and the differences can only be revealed by a detailed analysis. It is probably for this reason that only several classifications of this order were proposed during the last 50 years. Among these, the best known are the systems of Wagner (1939), Jordan (1948), and Smit (1982), Medvedev (1994, 1998).

Classification after J.Wagner

J.Wagner (1939) used the characters related to numerous structures, such as eyes, tentorial arms, genitalia, ctenidia, denticles, rows of setae, etc. In general, these characters were meristic, reflecting the presence/absence or the number of certain structures.

J.Wagner found out that flea families can be divided into 3 main groups based on the presence or absence of the squamulum (short process in the upper angle of the metepisternum) and the development of the interantennal groove.

1-st group: Pulicidae, Sarcopsyllidae (=Tungidae), Malacopsyllidae, Coptopsyllidae, Vermipsyllidae.

It includes the "Pulex- or Xenopsylla-like" fleas, usually having short and more or less rounded body. In the descriptions of families belonging to this group, Wagner noted the absence of the external interantennal groove and the presence of a frontal tubercle with upward-directed apex.

Fleas of the second and third groups possess a squamulum and have a more elongate and laterally flattened body.

2-nd group: Ctenopsyllidae (including the recent tribe Leptopsyllini, the subfamilies Hystrichopsyllinae, Stenoponiinae, Dinopsyllinae, Hypsophthalminae, and Doratopsyllinae, and the genus Palaeopsylla), Stephanocircidae, Ischnopsyllidae.

It unites "Ctenopsyllus- (Leptopsylla)-like" fleas with the head divided by the interantennal furrow (caput fractum).

3-rd group: Ceratophyllidae (the modern tribes Mesopsyllini and Caenopsyllini of the Leptopsyllidae, the subfamilies Neopsyllinae, Ctenophthalminae, Listropsyllinae of the Hystrichopsyllidae, subfamily Paradoxopsyllinae (Leptopsyllidae), Ceratophyllidae, Pygiopsyllidae, Xiphiopsyllidae.

This group of families was formed to comprise the "Ceratophyllus-like" fleas with undivided head (caput integrum and caput semifractum) and included a single family, which then had the taxonomic composition quite different from its modern interpretation.

Classification after K.Jordan

In 1948, K.Jordan published his classification of the order, which has become generally accepted with some additions. In an earlier publication (Jordan, 1947), the author outlined his approach to the flea taxonomy, staling that higher taxa of fleas can be established on the basis of character combinations, rather than individual characters, because every separate character may occur in representatives of other taxa as well.

Jordan divided the order into 2 superfamilies of unequal size, 16 families, and 32 subfamilies. The superfamily Pulicoidea included the families Pulicidae and Tungidae, whereas the superfamily Ceratophylloidea united the other 14 families. The main characters of Pulicoidea are the absence of denticles on metanotum and abdominal tergites, a single row of setae on tergites II-VII, absence of internal ridge on the outer wall of middle coxa and pseudosetae under the metanotal collar, and the metepimere strongly developed upwards. Even though each of these characters can be found outside this superfamily, their combination is unique.

Holland (1949) and Traub (1950) studied the articulation between the hypotendon and sternite IX or aedeagus, which helped to further improve Jordan's classification. The tribe Leptopsyllini was considered to be closely related to Ceratophyllidae. Later Johnson (1957) established a third superfamily Rhopalopsylloidea, subsequently renamed to Malacopsylloidea (Hopkins, 1958).

   ====== Pulicoidea
   |  === Malacopsylloidea
      === Ceratophylloidea
Jordan hypotesis with further additions

Unfortunately, Jordan did not have time to comment on his phylogenetic scheme, which was published in the Catalogue of Fleas in the British Museum (Hopkins, Rothschild, 1953) and in the review of flea studies prepared by Holland (1964). The analysis of this scheme shows that its branching sequence reflects the decreasing peculiarity of taxa. The families Pulicidae and Tungidae, having the most vivid distinctive features, were separated by Jordan as the first branch, comprising the superfamily Pulicoidea.

Classification after F.Smit

The next revision of the family-level classification of fleas was performed 30 years later by F.Smit (1982). According to this classification, the order is divided into 5 superfamilies:

1. Hystrichopsylloidea: Coptopsyllidae, Hystrichopsyllidae, Ctenophthalmidae, Stephanocircidae, Pygiopsyllidae

2. Ceratophylloidea: Ancistropsyllidae, Xiphiopsyllidae, Ceratophyllidae, Leptopsyllidae, Ischnopsyllidae,

3. Malacopsylloidea: Malacopsyllidae, Rhopalopsyllidae

4. Vermipsylloidea: Vermipsyllidae

5. Pulicoidea: Pulicidae, Tungidae.

This classification was based on characters related to 31 structures. Its new feature is the division of the family Hystrichopsyllidae into two families: Ctenophthalmidae and Hystrichopsyllidae proper. The latter is united with Macropsyllidae, probably because their representatives have paired spermathecae. On the basis of the same character, combined with the absence of denticles on the metanotum, Coptopsyllidae were included in the superfamily Hystrichopsylloidea.

Recent Problems of Flea Systematics

A more profound comparative anatomical investigation is necessary to further develop the classification of higher and lower flea taxa. In order to fill the extensive gaps existing in the skeleton morphology of fleas imago of different families and to introduce new characters in their classification S.G.Medvedev (Zoological Institute of Russian Academy of Science, S.-Petersburg, Russia) investigated the diversity of each structure of the flea skeleton, including head (Medvedev, 1982, 1983, 1988, 1989), thorax (Medvedev, 1990, 1991a, 1991b), and abdomen (Medvedev, 1992, 1993a, 1993b).

The small size of fleas and high complexity of shape and configuration of their structures necessitated the use of SEM. S.G.Medvedev examined 90 species of fleas, belonging to 52 genera; about 8000 microphotographs of different body structures were obtained. As a result, nearly 170 skeletal structures were investigated in representatives of 91% of all the genera and subgenera of the world flea fauna. On the basis of this information, the order was divided into 4 infraorders (Medvedev, 1994, 1998). When establishing the classification of the order, S.G.Medvedev proceeded from the assumption that a higher taxon is characterised not only by certain structural features of its representatives, but also by peculiarities of their distribution and biology. In view of this, the fundamental aspects of the geographical distribution and host-parasite relationships of the world fauna of fleas were analysed. This task was performed using a system of information retrieval and analysis developed in 1995-1999 (Medvedev, 1999) and capable of processing the data on geographical distribution of fleas (Medvedev, 1996a, 1996b) and their host-parasite relationships (Medvedev, 1997b, 1997c, 1998).

The last the most important news in flea systematic are recent investigations of DNA sequence (18 rDNA and etc) at Brigham Young University under Dr.Michael F.Whiting and Dr. Michael W.Hastriter which get new insight into phylogenetic relations of Siphonaptera.