Invertebrate Anatomy OnLine
Cat and dog fleas
Copyright 2001 by
is an exercise from Invertebrate
Anatomy OnLine , an
Internet laboratory manual for courses in Invertebrate Zoology. Additional
exercises can be accessed by clicking on the links to the left. A
glossary and chapters on supplies and laboratory techniques are also available. Terminology
and phylogeny used in these exercises correspond to usage in the Invertebrate
Zoology textbook by Ruppert, Fox, and Barnes (2004). Hyphenated
figure callouts refer to figures in the textbook. Callouts
that are not hyphenated refer to figures embedded in the exercise. The glossary
includes terms from this textbook as well as the laboratory exercises.
Mandibulata sP, Tracheata,
Hexapoda SC, Insecta C,
Dicondylia, Pterygota, Metapterygota, Neoptera, Eumetabola, Holometabola,
Siphonaptera O, Pulicoidea SF,
Archaeopsyllinae sF, (Fig
16-15, 20-14, 20-15, 21-23)
by far the largest and most diverse animal taxon, includes chelicerates,
insects, myriapods, and crustaceans as well as many extinct taxa. The
body is segmented and primitively bears a pair of jointed appendages on each
epidermis secretes a complex cuticular exoskeleton which must be molted to
permit increase in size. Extant
arthropods exhibit regional specialization in the structure and function of
segments and appendages. The body is typically divided into a head and trunk, of
which the trunk is often itself divided into thorax and abdomen.
gut consists of foregut, midgut, and hindgut and extends the length of the body
from anterior mouth to posterior anus. Foregut
and hindgut are epidermal invaginations, being derived from the embryonic
stomodeum and proctodeum respectively, and are lined by cuticle, as are all
epidermal surfaces. The
midgut is endodermal and is responsible for most enzyme secretion, hydrolysis,
coelom is reduced to small spaces associated with the gonads and kidney. The
functional body cavity is a spacious hemocoel divided by a horizontal diaphragm
into a dorsal pericardial sinus and a much larger perivisceral sinus. Sometimes
there is a small ventral perineural sinus surrounding the ventral nerve cord.
hemal system includes a dorsal, contractile, tubular, ostiate heart that pumps
blood to and from the hemocoel. Excretory
organs vary with taxon and include Malpighian tubules, saccate nephridia, and
organs also vary with taxon and include many types of gills, book lungs, and
nervous system consists of a dorsal, anterior brain of two or three pairs of
ganglia, circumenteric connectives, and a paired ventral nerve cord with
segmental ganglia and segmental peripheral nerves. Various
degrees of condensation and cephalization are found in different taxa.
is derived with centrolecithal eggs and superficial cleavage. There
is frequently a larva although development is direct in many. Juveniles pass
through a series of instars separated by molts until reaching the adult size and
reproductive condition. At
this time molting and growth may cease or continue, depending on taxon.
includes arthropods in which the third head segment bears a pair of mandibles. As
currently conceived this taxon includes myriapods, hexapods, and crustaceans. Appendages
may be uni- or biramous and habitats include marine, freshwater, terrestrial,
and hexapods share tracheae and a single pair of antennae and are sister taxa in
which have gills and lack tracheae, are excluded and form the sister group.
body is divided into three tagmata; head, thorax, and abdomen. Appendages
are uniramous and a single pair of antennae is present. Three
pairs of legs and two pairs of wings are found on the thorax of most adults. Hexapod
legs are uniramous although there is increasing evidence that they evolved from
multiramous appendages of their ancestors. Gas
exchange is accomplished by trachea. Excretory
organs are Malpighian tubules and the end product of nitrogen metabolism is uric
is relatively little cephalization of the nervous system. Insects are gonochoric
with copulation and internal fertilization.
hexapods are insects. A
few hexapod taxa (orders) lack wings and have primitive mouthparts recessed into
the head and belong to Entognatha, the sister taxon of Insecta. Insects
have ectognath mouthparts and the adults (imagoes) of most taxa have wings.
winged insects. These insects are derived from a winged common ancestor. Adults
of most taxa have wings although they have been lost in some.
have no ocelli and there are six or fewer Malpighian tubules.
final larval instar pupates and undergoes a radical metamorphosis in which it is
converted to an imago, or adult. The
imago is sexually mature and in most taxa has wings whereas larvae are immature
and wingless. During
metamorphosis many or most larval tissues are dismantled and adult structures
built anew. Wings,
for example, are manufactured from clusters of undifferentiated cells known as
imaginal discs but not from preformed wingpads as in pauro- and hemimetabolous
are small, secondarily wingless, laterally compressed blood sucking insects.
Most fleas are mammalian ectoparasites but about 5% parasitize birds. About 2400
extant species are known. Like most parasites, fleas are highly derived and
mouthparts are adapted for piercing and sucking and mandibles are lacking. Because
of their highly derived condition zoologists have encountered difficulties in
recognizing homologies between flea mouthparts and those of other insects. A
blood meal is required prior to oviposition. Many are disease vectors. The
cuticle is sclerotized and hard and the entire body surface is protected by
pair of ocelli may be present but compound eyes are absent. Development is
holometabolous and the larvae are slender and wormlike. Larvae are not parasitic
and feed on organic detritus, including partially digested host blood in the
feces of the adults. Fleas
are adapted for passing rapidly and unimpeded through the hair or feathers of
the host. Adaptations for this are the smooth, compressed body, absence of
wings, posteriorly pointing spines and setae, and short antennae that can be
sequestered in a fossa on the side of the head. Attempts
by the host to remove the flea are impeded by the backward pointing setae and
arose from winged ancestors and are probably related to Mecoptera (Scorpion
flies) and Diptera (flies).
fleas, Ctenocephalides felis,
and dog fleas, Ctenocephalides
canis, can be collected from a cooperative pet in quantities limited only
by the pet’s (and collector’s) patience. The
two species are similar, in fact are difficult to distinguish from each other,
and either is suitable for this exercise. Both are cosmopolitan and both occur
on cats and dogs, and occasionally humans. The human flea, Pulex
irritans, is also cosmopolitan and belongs to the same family (Pulicidae). Cleared
wholemount slides of C. felis, C.
canis, P. irritans, and Xenopsylla
cheopis(the rat flea and also a member of the same family) are available
from biological supply companies. Unmounted
or mounted specimens can be used for this exercise. Unmounted
specimens should be observed with the dissecting microscope, wholemounts with
the compound microscope. The dog flea, C.
canis, is the intermediate host of the dog tapeworm, Dipylidium
caninum, found in both dogs and cats. The
rat flea, X. cheops, is a
vector of bubonic plague. Haplopsyllus
anomalus, another pulicid, is a parasite of California ground squirrels and
is also a plague vector. In the eastern United States Ctenocephalides
felis is the species most often
found in human dwellings whereas on the Pacific coast it is Pulex
other insects, fleas have a body consisting of three tagmata; head, thorax, and
abdomen (Fig 1, 21-22A). Unlike
most other insects, however, the distinction between the tagmata is not distinct
and it is not obvious at a glance where one tagma bends and another begins.
Figure 1. The cat flea, Ctenocephalides
have been omitted for clarity. Siphon13L.gif
that of other insects, the head is enclosed in a sclerotized cranium known as
the head capsule (Fig
2). The capsule is a single unit formed by the fusion of the sclerites of the
head segments, which are themselves no longer recognizable. The
head capsule is divided into anterior and posterior regions by a thick
cuticularized ridge, the falx,
arching transversely from one side of the head to the other.
head capsule consists of the typical regions characteristic of insects. The
front of the head, anterior to the falx, is the frons. The
top of the head is the vertex.
The posterior region, near the thorax, is the occiput. The gena is
ventral and posterior to the ocellus.
articulation between the anterior head capsule and the posterior region is
slightly flexible in some taxa (Fracticipita sO)
but not in others (Integricipita sO)
such as Ctenocephalidesand
other pulicids. The falx marks the zone of articulation between the two regions.
In Ctenocephalides the
ventral margin of the gena bears agenal ctenidium (ctene
= comb) consisting of a comblike row of strong, stout, heavily sclerotized
spines (Fig 1,2). OnlyCtenocephalides have
genal ctenidia with more than five spines (Fig 1).
Figure 2. Lateral view of the head of a cat
flea, Ctenocephalides felis.
eyes are lacking. Lateral
ocelli present in some taxa,
including Ctenocephalides (Fig
ocellus has a single lens.
to the falx is a lateral depression, the antennal
fossa, in which the antenna are sequestered. The
antenna can be moved out of the way into the fossa so they do not get snagged on
the hair of the host. A
strong, spine-tipped genal
lobe projects posteriorly
from the gena over the antennal fossa to further protect the antenna from
snagging on the pelage of the host.
The antennae are
multiarticulate but the terminal nine or so articles are short, wide, and appear
to form a single large, clublike article, known, appropriately, as the club Fig
two proximal articles are large and distinct. The
antenna is in an unusual position on the side of the head where it lies out of
the way in a recess, the antennal
fossa. During copulation males deploy their antennae and use them to
hold the female.
mouthparts are adapted for piercing and sucking (Fig 2, 3). The long slender stylet,
which is the piercing organ, is formed of two slender, bladelike maxillary
lacinia and a needlelike epipharynx (Fig 2). The stylet is supported by the
labium. The labrum and hypopharynx are vestigial and mandibles are absent.
unpaired, median epipharynx extends
ventrally from the lower surface of the head, anterior to the mouth (Fig 2,3). In
the past it was thought to be the labrum but it is now considered to be an
outgrowth of the head capsule. It
is long slender and bladelike.
The maxilla bears
two laciniae and
two maxillary palps with
4-5 articles (Fig 2). The
maxillary laciniae are long and slender and form the outer part of the stylet
(Fig 3). The serrated, sawlike laciniae are used to cut into the skin of the
host, permitting the epipharynx to slip into a blood vessel. In the past the
laciniae were thought to be the highly modified mandibles but it is now believed
that mandibles are absent in fleas. Linnaeus
believed the maxillary palp, because of its morphology and position, to be the
two laciniae and the epipharynx together enclose a food channel for inbound
blood (Fig 3). The
laciniae form a smaller salivary channel for outbound saliva. The maxillae have
antenniform, sensory maxillary palps.
The labium is
represented by a proximal prementum and
two 3-4 articulate labial
palps which form a sheath
around the stylet (Fig 2,3). The
labium is not part of the stylet and it does not enter the host. Instead, it
supports and guides the stylet.
to pull blood into the stylet and gut is provided by cibarial and pharyngeal
pumps. The walls of the cibarium (Fig 21-7) and of the pharynx have radial
muscles whose contractions dilate their respective lumina to create suction.
three thoracic segments (prothorax, mesothorax, and metathorax) are subequal in
size but are not as easily recognized as are those of other insects. Each bears
a pair of legs and is covered by several sclerites. Dorsally
the prothorax, mesothorax,
and metathorax are
covered by the pronotum, mesonotum,
respectively. These three sclerites are the best landmarks for recognition of
the segmentation of the thorax.
Figure 3. Diagrammatic representation of a
generalized flea stylet in cross section. Siphon15L.gif
the segments are protected by sternites. The large prosternum extends
under the head capsule, giving the impression that the forelegs arise from the
head (Fig 1). Ctenocephalides has
a conspicuous pronotal
ctenidium (similar to the
genal ctenidium) along the posterior border of the pronotum (Fig 1,2). Although
wings are absent in fleas, some entomologists believe two posterior sclerites,
the mesepimeron and metepimeron of the mesothorax and metathorax, respectively,
are vestiges of the forewings and hindwings of the winged ancestors.
thoracic segment bears a pair of legs, which resemble each other except that the
hindlegs are larger and adapted for jumping (Fig 1). The
segments and their legs are; prothorax and forelegs,
mesothorax and midlegs,
and metathorax and hindlegs. The
legs consist of coxa, trochanter,
femur, tibia, tarsus and tarsal
claws, in sequence from proximal to distal. The coxae and femora are
large and flattened. The
tarsi comprise five tarsomeres,
with large, terminal tarsal claws. The legs are heavily spinose.
fleas are wingless they posses lateral sclerites (discussed above) on the
mesothorax and metathorax that may be wing vestiges.
abdomen is ten-segmented (Fig 1). Most segments are covered by a dorsal tergite and
a ventral sternite.
Segments 8-10 are the genital segments and the tenth tergite has a complex
sclerite, the pygidial plate (=
sensillium), equipped with slender trichobothria-like setae apparently sensitive
to weak air currents (Fig 1). Ten pairs of stigmata are
present, two thoracic and eight abdominal, and open into the tracheal system.
fleas live on mammals or birds, on whose blood they feed. Mating occurs on the
host and eggs are produced to drop from the host into the host’s nest or
domicile. First instar larvae hatch from the eggs and feed on organic debris in
the nest. The
larvae are not parasites and do not live on the body of host, rather live in its
nest. The feces of adult fleas
contains abundant partially digested host blood which contributes to the supply
of organic detritus in the nest and is an important food source for the larvae.
Larvae are wormlike, with head capsule, but no legs. Larvae
have primitive mandibulate (biting and chewing) mouthparts, unlike those of the
adults, and unmodified for piercing and sucking. Eventually the larvae spin a
cocoon and pupate, still in the nest. Development
is holometabolous and imagoes emerge from the pupa and move onto the host.
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An introduction to entomology. Comstock Publishing, Ithaca NY. 1044pp.
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Cat or dog flea