Cockroach: Periplanata americana

Morphology

Cockroaches are household pests.  They are usually black or brown bodied. They are also the vectors of several diseases.

Habitat

Cockroaches are nocturnal omnivores.  They are found in wet and damp places.

External appearance

  • Cockroaches are triploblastic and bilaterally symmetrical organisms.
  • They have a dorsoventrally compressed body.
  • The size can range from 1 to 3 inches.

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  • The whole body is covered by a hard chitinous exoskeleton which occurs in the form of plates called sclerites.
  • The dorsal plate is called terga and the ventral plate is called sterna.
  • They are joined together by a thin, flexible and movable membrane called arthrodial membrane or pleura.
  • The body is divided into three parts – Head, Thorax and Abdomen.

 

Head

Head is triangular and it is movably attached to the thorax by a neck.  It consists of 6 fused elements. The head bears a pair of antennae, a pair of compound Eyes and mouthparts.

  • Antenna is the tactile and olfactory organ of the Cockroach.  It helps to monitor the environment.
  • Each compound eye is made up of thousands of small units called ommatidia.
  • Each ommatidia forms distinct images of an object. All these images overlap to form a complete image of the object.  This type of vision is termed as mosaic vision.

The mouthparts consist of a labrum or upper lip, a pair of mandibles, a pair of maxillae and a labium or lower lip. A median chitinous structure acts as the tongue or the hypopharynx.  Sensory hairs are present on it.

Thorax

Thorax has three segments – prothorax, mesothorax and metathorax.

  • Each segment bears a pair of legs.
  • Two pairs of wings arise from the dorsal surface – one pair from mesothorax and the other pair from metathorax.
  • The fore wings are opaque, dark and leathery, and are called tegmina.
  • The hindwings are transparent and are used in flight.

  • Each leg has 5 segments – Coxa, Trochanter, Femur, Tibia and Tarsus.
  • Coxa – It is the basal segment. It attaches the leg to the body.

  • Trochanter – It is the joint between coxa and femur.
  • Femur – It is a long and broad part of the leg.
  • Tibia – It is the thick and bears small bristles.
  • Tarsus – It bears 5 segments called tarsomeres.

Abdomen

  • The abdomen in adult males and females consists of 10segments.
  • In females, the 7nth sternum is boat shaped.
  • The 7nth, 8th and 9nth sterna together form a brood or genital pouch whose anterior part contains female gonopore, spermathecal pores and collateral glands.

  • In males, genitalpouch or chamber lies at the hind end of abdomen.
  • It contains dorsalanus, ventral male genitalpore and gonapophysis.
  • Males bear a pair of short, thread-like anal styles which are absent in females.

  • In both sexes, the 10th segment has a bilobed tergum, and bears a pair of jointed filamentous structures called anal cerci.
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