Morphology of grasshopper Body segmentation

 

Morphology of grasshopper Body segmentation - Structure of Head, thorax and abdomen

                        Insect body is differentiated into three distinct regions called head, thorax and abdomen (grouping of body segments into distinct regions is known as tagmosis and the body regions are called as tagmata).

I. HEAD

                     First anterior tagma formed by the fusion of six segments namely preantennary, antennary, intercalary, mandibular, maxillary and labial segments. Head is attached or articulated to the thorax through neck or Cervix. Head capsule is sclerotized and the head capsule excluding appendages formed by the fusion of several sclerites is known as Cranium.

Sclerites of Head

i.   Vertex: Summit of the head between compound eyes.
ii.  Frons: Facial area below the vertex and above clypeus.
iii. Clypeus: Cranial area below the frons to which labrum is attached.
iv.  Gena: Lateral cranial area behind the compound eyes.
v.   Occiput: Cranial area between occipital an post occipital suture.

Sutures of Head

i. Epicranial suture: (Ecdysial line) Inverted `Y' shaped suture found medially on the top of head, with a median suture (coronal suture) and lateral suture (frontal suture).
ii. Epistomal suture: (Fronto clypeal suture) found between frons and clypeus.
iii. Clypeo labral suture: Found between clypeus and labrum.
iv. Post occipital suture: Groove bordering occipital foramen. Line indicating the fusion of maxillary and labial segment.

Posterior opening of the cranium through which aorta, foregut, ventral nerve cord and neck muscles passes is known as Occipital foramen. Endoskeleton of insect cuticle provides space for attachment of muscles of antenna and mouthparts, called as Tentorium. The appendages like a pair of compound eyes, 0-3 ocelli, a pair of antenna and mouth parts are called as Cephalic appendages.

Functions of Head

i.   Food ingestion
ii.  Sensory perception
iii. Coordination of bodily activities
iv.  Protection of the coordinating centers

TYPES OF INSECT HEADS

Based on the inclination of long axis of the head and orientation of mouth parts there are three types of insect heads.

1)  HYPOGNATHOUS (Hypo – below; gnathous – jaw)

This type is also called orthopteroid type. The long axis of the head is vertical. It is at right angles to the long axis of the body. Mouth parts are ventrally placed and project downwards.

2)  PROGNATHOUS (Pro- infront ; gnathous – jaw)

This type is also called coleopteroid type. The long axis of the head is horizontal. It is in line with the long axis of the body. Mouth parts are directed foreward. Eg: groung beetles.

3)  OPISTHOGNATHOUS (Opistho – behind ; gnathous – jaw)

This type is also called hemipteroid type or opisthorhychous. Head is deflexed. Mouth parts are directed backwards and held in between the fore legs. Eg: Stink bug.

II. THORAX

                           Second and middle tagma which is three segmented, namely prothorax, mesothorax and metathorax. Meso and metathorax with wing are called as Pterothorax. Thorax is made up of three scleritic plates namely, dorsal body plate (Tergum or Nota, ventral body plate (Sterna) and lateral plate (Pleura).

Thoracic nota: Dorsal body plate of each thoracic segments are called as pronotum, mesonotum and metanotum respectively.

Pronotum: this sclerite is undivided and Saddle shaped in grass hopper, Shield like in cockroach.

Pterothoracic notum: Have 3 transverse sutures (Antecostal, Pre scutal and Scuto-scutellar) and 5 tergites(Acrotergite, Prescutum, Scutum, Scutellum and Post-scutellum)

Thoracic sterna: Vental body plate of each thoracic segments are called as prosternum, mesosternum and metasternum. Thoracic sterna is made up of a segmental plate called Eusternun and a intersternite called Spinasternum. Eusternum is made up of three sclerites viz., presternum, basisternum and sternellum.

Thoracic pleura: Lateral body wall of thoracic segment between notum and sternum. Selerites of pleuron is called as pleurites and they fuse to form Pleural plate. Pleural plate is divided into anterior episternum and posterior epimeron by Pleural suture. Pterothoracic pleuron provides space for articulation of wing and le.g. Thoracic appendages are three pairs of legs and two pairs of wings. Two pairs of spiracles are also present in the mesopleuron and metapleuron.

Functions of thorax: Mainly concerned with locomotion.

III. ABDOMEN

Third and posterior tagma. This tagma is made up of 9-11 Uromeres (segments) and is highly flexible. abdominal segments are telescopic in nature and are interconnected by a membrane called conjunctiva. Each abdominal segment is made up of only two sclerite namely dorsal body plate (tergum) and ventral body plate (sternum). Eight pairs of spiracles are present in the first eight abdominal segments, in addition to a pair of tympanum in the first abdominal segment. Eight and ninth abdominal segments contains the female genital structure and ninth segment with male genital structure. Abdominal appendages are genital organs and cerci.

Function: Concerned with reproduction and metabolism.