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Caput (head): The head of a flea bears important structures, such as the mouth-parts,
the antenna, and in a lot of cases a genal comb. It can be very specialized, having
additional structures, such as helmets or frontal tubercles. Fleas can have integricipit
heads or fracticipit heads. If an interantennal suture is absent or lacking, we
speak of an integricipit head, if it is present, we have a fracticipit head. The
eye can vary tremendously in its size and sclerotization, some fleas have vestigial
eyes.Click Here for Detail
Thorax (chest): The thorax is divided into three parts, the pro-, meso-, and metathorax.
Each thoracic segment is itself composed of three parts, denoted as -notum, -epimeron
and -sternum. (Therefore we will have a pronotum, a proepimeron and a prosternum
and so on).
Sternites: Sternites are the ventral (lower) sclerotized shields of the abdomen.
(see also tergites)
Tergites: Tergites are the dorsal (upper) sclerotized shields of the abdomen. The
name is rarely used without a qualifying numeral (et. t IX). All tergites (and also
sclerites) are linked by connective flexible cuticles, which are folded inwards,
if the flea is unfed. In case the flea ingests a bloodmeal, the abdomen will be
able to expand, just like a telescope. Each tergal (and also sternal) abdominal
segment has one segmental nerve, coming from a ganglion of the ventral nerve cord,
and a segmental tracheid, coming from the dorsal tracheal complex.
Abdomen: The abdomen is composed of several abdominal segments (10), the upper portion
are the tergites, the lower portion the sternites. Some abdominal segments are transformed
into parts of the genitalia.
Sensilium (Pygidium): This is a sensory organ peculiar to fleas. It is saddle-shaped
and consists of a group of receptors, set in a regular array in a bed of small,
thick cuticular spines. Different species tend to have different numbers of those
receptor groups. The function of this structure is not very well understood.
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Terminalia and Genitalia: This describes the last abdominal tergites and sternites
which are part of the male and female reproductive organs or encase them.
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