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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 DetailThorax (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.
Click Here for DetailTerminalia 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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