Morphology of Cockroach: Classification and Segmentation

Morphology of Cockroach: We have seen these insects in our kitchen, haven’t we? These animals belong to the largest animal phylum, i.e., Arthropoda and the largest class Insecta. The Morphology of Cockroaches involves external features like the exoskeleton of cockroaches, its body segments, moth parts, legs, wings, etc.

Based on the external morphology of cockroaches, males and females can be easily differentiated. This method of differentiation of sexes based on external morphology is called sexual dimorphism. Read this article to know more about the Morphology of Cockroaches and various other facts related to their morphology.

Classification of Cockroach

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Blattodea
Genus: Periplaneta
Species: Americana

Fig: Cockroach

General Characteristics of Cockroach

Some of the general characteristics of cockroach are as follows:
i. They are brown or black-bodied animals that are included in class – Insecta of phylum – Arthropoda.   
ii. Three species of cockroaches are commonly found in India, i.e., Periplaneta americana – American cockroach, Blatta orientalis – Bombay canary and Blattella germanica – Ship cockroach.
iii. Their body is elongated, dorsoventrally flattened and is divided into three segments, i.e. head, thorax and abdomen.
iv. They have a long antenna, three pairs of legs, two pairs of wings, various mouthparts and various other sensory structures.
v. They are nocturnal omnivorous and scavenger animals, i.e., they are active at night, and they can eat both plant and animal products.
vi. These cockroaches are worldwide and found in such places of human dwellings when darkness, warmth, dampness and plenty of organic debris are available.
vii. These are cursorial, i.e., run fast, dioecious and oviparous and exhibit parental care.
viii. The digestive system of cockroach consists of an alimentary canal and digestive glands.
ix. Anatomy of cockroach: Each cockroach has eyes, a mouth, salivary glands, antennae, brain, heart, colon, reproductive system, mid-guts, legs, oesophagus, gastric caeca, fat bodies and malpighian tubules.

Morphology of Cockroach

Now, let us study the Morphology of Cockroach in detail:

Fig: Morphology of Cockroach Diagram

Morphology of Cockroach: Shape, colour and size

i. These cockroaches come in reddish-brown to brown in colour.
ii. Their size ranges from \(0.25\) inches to \(3\) inches and the body is elongated, dorsoventrally flattened and is divided into three segments, i.e. head, thorax and abdomen.
iii. They have a long antenna, three pairs of legs, two pairs of wings, various mouthparts and various other sensory structures.

Morphology of Cockroach: Segmentation

i. The adults of the common species of cockroach – Periplaneta americana are about \(34\) to \(53\) mm long with wings that extend beyond the tip of the abdomen in males.
ii. The body shows three regions or tagmata that includes the head, thorax and abdomen.
iii. Embryologically, the body is formed of \(20\) segments – \(6\) in the head, \(3\) in the thorax and \(11\) in the abdomen.
iv. Only \(10\) segments are retained in the abdomen of the adult, in which only the first \(7\) are distinct in females, and the first \(9\) are distinct in males.
v. The anus is located at the end of the \({10^{{\rm{th}}}},\) modified segment.

Morphology of Cockroach: Exoskeleton

i. The body of a cockroach is narrow, elongated, bilaterally symmetrical, segmented and dorsiventrally flattened.
ii. The entire body is covered by a hard chitinous covering called an exoskeleton.
iii. The exoskeleton of each segment contains plate-like structures called sclerites.
iv. Articular or arthrodial membrane connects adjacent sclerites to each other. It is flexible and soft and helps in cursorial nature.
v. The exoskeleton protects the body and provides rigidity and surface for the attachment of muscles. It also prevents the loss of water from the body.
vi. The dorsal surface of the abdomen and thorax is covered by chitinous plates called tergum.
vii. The ventral surface of the abdomen and thorax is covered by chitinous plates called the sternum.
viii. In the lateral sides, tergum and sternum plates are connected with the help of a membrane called the pleura.
ix. Pleurites are the various small sclerites associated with pleura.

Body Morphology of Cockroach

The cockroach body is divided into three parts, i.e., head, thorax and abdomen.

Fig: Cockroach Head

1. Head

i. The head is triangular and is formed by a fusion of \(6\) chitinous or sclerite plates.
ii. The head is bent downwards in a hypognathous position, i.e., at an angle of \({90^{\rm{o}}}\) from the long axis of the body.
iii. All sclerites of the head fuse to form a head capsule.
(a) Compound eyes
i. The head capsule bears a pair of compound eyes. Each eye is composed of about \(2000\) hexagonal units bearing a sensory structure called ommatidia.
ii. Each ommatidium has a biconvex lens formed by the cuticle.
iii. The compound eye produces a vision that has high sensitivity but low resolution. Thus, it is responsible for mosaic or nocturnal vision.
iv. Fenestrae or ocellarspots are located near compound eyes; these are also called ocelli or simple eyes, which help to distinguish bright and dim lights.
(b) Antennae
i. A pair of antennae arise from the membranous sockets, i.e. antennal sockets that present in front of the eyes can move in all directions, and they are very sensitive.
ii. Each antenna is formed of \(3\) segments – scape (largest), pedicel (narrow and elongated) and flagellum (the long and slender part which has many jointed parts, bearing tactile sensory setae).
iii. These antennae act as sense organs of touch and smell. It has tactile (touch) and olfactory receptors (smell).
(c) Mouth
i. The anterior end of the head bears appendages forming biting and chewing type of mouthparts.
ii. The mouth parts consist of the labrum (upper lips), mandibles (jaws), maxillae (additional jaws), labium (lower lips) and hypopharynx (tongue).
iii. Labrum: It is also called the upper lip. It helps in holding the food and protecting the mouth.
iv. Mandibles: A pair of jaws (mandibles) present on either side of the mouth and helps in biting the food.
v. A pair of maxillae are present below the mandibles. They help in holding and pushing the food into the mouth.
vi. Labium: It is also called the lower lip. It covers the mouth from the ventral side.
vii. Hypopharynx: It is also called the tongue. It is a tubular structure present above the labium between mandibles. The salivary ducts open as their base.

Fig: Mouth Parts of Cockroach

2. Thorax

Thorax is made up of three segments, prothorax, mesothorax and the last one, metathorax. The prothorax is the anterior segment of the thorax of an insect, and this segment does not bear any wings. The Head is connected to the prothorax through a slender neck. Each mesothorax and metathorax bears a pair of wings.
Thoracic appendages
These appendages include legs and wings.
(a) Legs
i. Each thoracic segment laterally bears a pair of legs articulated to its pleurites.
ii. All legs are structurally similar and formed of \(5\) main segments called coxa, trochanter, femur, tibia and tarsus.

Fig: Cockroach Leg

(b)   Wing 

i. These are two pairs; the first pair is mesothoracic – attached with the tergum of the mesothorax and the second pair is metathoracic – connected with the tergum of the metathorax.
ii. Wings are the membranous outgrowths of the body wall, which are supported by veins that communicate with haemocoel.
iii. An air tube called the trachea, and a fine nerve is also present. The movement of the wings is controlled by a special set of muscles.
iv. Mesothoracic Wings are also called wing-covers or tegmina or elytra. These are thick, large, leathery, dark coloured opaque in structure which are narrow at the distal end. They are not used for flight but cover and protect metathoracic wings.
v. Metathoracic wings are very delicate, transparent, thin and membranous with a broad terminal end. These wings are used for flight, but in the resting position, they lie folded below the tegmina.

3. Abdomen

i. Its sclerites are relatively thinner.
ii. There are \(10\) tergites in both males and females.
iii. Ventrally, the abdomen has only \(9\) sternites in males and seven in females.
iv. In females, the last, i.e., \({7^{{\rm{th}}}}\) sternite, is larger and boat-shaped. Together with the indistinct 8th and sternites, it forms a chamber-like structure called gynatrium.
v. The posterior part of gynatrium is called the oothecalchamber because ootheca is formed in it. Behind this chamber, the \({7^{{\rm{th}}}}\) sternite bifurcates into two prominent oval plates called gynovalvularplates or apical lobes.

Abdominal appendages: Abdominal segments lack locomotory appendages. At the posterior end, however, there are certain small structures associated with the gonopore. These are different in both sexes. It includes anal cerci, anal styles and gonapophyses.
(a) Anal Cerci – These are paired and jointed outgrowths that arise from the \({10^{{\rm{th}}}}\) tergum. These are sensitive to sound and other vibrations.
(b) Anal Styles – These are also paired but thin and small unjointed outgrowths that projects backwardly from the sides of the \({9^{{\rm{th}}}}\) sternum of male cockroach only. These are also sensitive to touch.
(c) Gonapophyses – In both males and females, the genital aperture is surrounded by some sclerites called gonapophyses. In males, they arise from the \({9^{{\rm{th}}}}\) segment and form the external genitalia or external genital organs to help the insect in the copulation process. In female cockroaches, gonapophysis belongs to the \({8^{{\rm{th}}}}\) and \({9^{{\rm{th}}}}\) abdominal segments to form an ovipositor. The latter is used to guide the fertilized eggs towards the oothecal chamber for ootheca formation.

Fig: Structure of Anal cerci and Anal style

Male and Female Cockroach

Cockroaches are dioecious and show sexual dimorphism. The male and female cockroaches are different in morphology, and the difference is given in a tabular column below.

Summary

The cockroach is a nocturnal, omnivorous animal. It belongs to the kingdom Animalia, phylum Arthropoda and class Insecta. The cockroach body is elongated, dorsoventrally flattened, and reddish-brown in colour. Their entire body is covered with a hard chitinous exoskeleton. The body is divided into three segments, i.e., head, thorax and abdomen. The mesothorax and metathorax have a pair of wings. However, the pair of wings attached to the metathorax region only help them in flight. These have three paired legs, one pair attached to each thoracic segment. In cockroaches, males and females have slightly different morphology, and therefore they show sexual dimorphism. One of the distinguishing features is the presence of anal styles that are found only in males and females who lack anal styles.

Frequently Asked Questions (FAQs) on Morphology of Cockroach

The commonly asked questions about Morphology of Cockroach are answered here:

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