Question

Describe the external morphology of cockroach.​

Answer 1

AnsWer :

External features of cockroach:

• Cockroach is triploblastic, bilaterally symmetrical, dorso-ventrally flattened, coelomate animal.

• The adult measures from 3 to 5 cm in length and 1.5 to 2 cm in breadth.

• Their colour is reddish brown.

• Hard, waxy, water proof chitinous exoskeleton protects the body of the cockroach.

• It is made up of polysaccharide called chitin.

• Each segment is divided into four plates namely dorsal tergum, ventral sternum and two lateral pleurons.

• Body divisions: The body is divided into three regions namely: head, thorax and abdomen.

a.) Head:

• The head is oval, dorso-ventrally flattened and is pear shaped, attached at the right angles to the thorax by a thin, narrow, movable neck or cervix.

• Hence, the broad end is directed upwards and the narrow end is directed downwards.

• Head is made up of six sclerites. These fuse in adults and forms head capsule.

• Head bears four important parts: compound eyes, antennae, fenestrae and mouth parts.

Compound eyes:

• Compound eyes are paired, dark, kidney shaped structures placed on the lateral sides of the head.

• They are made up of large number of hexagonal facets called ommatidia (singular ommatidium).

Antennae:

• Antennae are paired, long, slender, filamentous, many jointed structures present between the compound eyes.

• They are lodged in the membranous pits called antennal sockets and are the tacto receptors or organs of olfaction (sense of smell).

Function: They are useful in localizing the food material in the vicinity.

Fenestrae:

Fenestrae also called as oscillar spots are situated at the base of each antenna and appears as white spots.

Mouth parts or trophi:

• Mouth parts of cockroaches are of chewing and biting type.

• These are movable segmented appendages which assist in ingestion of food.

• It includes labrum, mandibles, maxillae, labium and hypopharynx.

b) Thorax:

• Thorax is made up of three distinct segments as prothorax, mesothorax and metathorax

• Dorsally, the thorax bears two pairs of membranous wings- fore wing and hind wings.

• Fore wings are first pair of dark, opaque, thick wings which are protective in function.

• Hind wings are thin, broad, membranous, delicate and transparent

• Hind wings are useful in flight and hence, are also called true wings.

• Three pairs of thoracic legs are present on ventral side.

c) Abdomen:

• The abdomen is the largest of the three regions.

• Its segmentation is conspicuous both dorsally and ventrally

• The abdomen consists of 11 segments of which 11th is reduced and fused with the 10th, so that only ten segments are distinct and visible.

• Dorsally, each segment is covered by a tergite and ventrally by a sternite.

• Laterally, tergites and sternites are connected by unsclerotized flexible muscles.

• Anal styles are present in segment 9 in males.

• Segment to bears a pair of large, segmented cerei, which are visible in both dorsal and ventral views in both males and females.

• These are sensitive to air movements, including sound and perhaps to ground vibrations.

• Eight pairs of spiracles are present in the abdomen.

• Genital openings are present on different segments in both the sexes and are surrounded by chitinous plates in both, which are collectively called gonapophyses.