Pleural Regions Of The Thorax

Apterygota and Immature Plecoptera The anapleurite is the sclerotized area above the coxa (supracoxal area) (Fig. 8). The coxopleurite is a sclerotized plate situated between the coxa and the anapleurite (Fig. 8). It bears the dorsal coxal articulation, the anterior part of which becomes the definitive trochantin. The sternopleurite, or coxosternite, is the definitive sternal sclerite that includes the areas of the limb bases and is situated beneath the coxa (Fig. 8).

Pterygota The basalare is a sclerite near the base of the wing and anterior to the pleural wing process (Fig. 9). The basalare serves as a place of insertion for the anterior pleural muscle of the wing. The subalare is posterior to the basalare and the pleural wing process (Fig. 9). It too serves as a place for insertion of the wing's posterior pleural muscle. The tegula

FIGURE 8 Pleural aspect of the apterygote thorax: diagrammatic.

is the anterior most independent sclerite associated with the wing base. The tegula is typically scalelike, articulates with the humeral sclerite, and protects the wing base from physical damage. The tegula is absent from Coleoptera and from the metathorax of most orders. The pleural wing process is located at the dorsal end of the pleural ridge and serves as a fulcrum for the movement of the wing (Fig. 9). The parapteron is a small sclerite, articulated on the dorsal extremity of the episternum just below the wings (Fig. 7).

The pleural suture is an easily visible landmark on the pterothoracic pleura (Fig. 9). It extends from the base of the wing to the base of the coxa. The pleural ridge is formed internally by the pleural suture and braces the pleuron above the leg. The episternum is a pleural sclerite anterior to the pleural suture and sometimes adjacent to the coxa (Fig. 9); the episternum is typically the largest lateral thoracic sclerite between the sternum and the notum. The epimeron is the posterior division of a thoracic pleuron adjacent to the coxa and posterior to the pleural suture (Fig. 9); it is typically smaller than the episternum and narrow or triangular. The episternum and the epimeron of many insects have become subdivided into several secondary sclerites bounded by sutures. The simplest condition shows the episternum divided into a dorsal anepisternum and a ventral katepisternum (Fig. 9). Similarly, the epimeron is divided into an anepimeron and katepimeron. The trochantin is a small sclerite at the base of the insect leg of some insects (Figs. 7, 9). Some workers theorize that the trochantin may have developed into the pleural wall. The trochantin is often fused to the episternum or absent.

The precoxal bridge is anterior to the trochantin, usually continuous with the episternum, frequently united with the

Pleural process

Katepisterum

Mesepisternum Mesepimeron

Anepisterum

Precoxal bridge Trochantin

Pleural process

Katepisterum

Mesepisternum Mesepimeron

Anepisterum

Precoxal bridge Trochantin

Pleural suture

Spiracle Anapleurite Coxopleurite Coxal opening Postcoxal bridge Coxosternite

FIGURE 9 Lateral aspect of the pterygote thorax (Orthoptera: Acrididae).

Pleural suture

Spiracle Anapleurite Coxopleurite Coxal opening Postcoxal bridge Coxosternite

FIGURE 9 Lateral aspect of the pterygote thorax (Orthoptera: Acrididae).

basisternum, but also occurs as a distinct sclerite (Fig. 9). The postcoxal bridge is the postcoxal part of the pleuron, often united with the sternum behind the coxa (Fig. 9). The sclerite extends behind the coxa and connects the epimeron with the furcasternum. The meron is a lateral, postarticular basal area of the coxa and is sometimes found disassociated from the coxa and incorporated into the pleuron. The meron is typically large and conspicuous in panorpid and neuropteran insects. In Diptera the meron forms a separate sclerite in the thoracic pleuron.

Ventral Aspect

The ground plan of the sternum (Greek, sternon = chest; pl., sterna) consists of four sclerites, including an intersternite (spinasternite), two laterosternites (coxosternites), and a mediosternite (Fig. 10). The mediosternite and the lateros-ternite meet and join, and the line of union is called the laterosternal sulcus (pleurosternal suture) (Fig. 10).

Paired furcal pits are found in the laterosternal sulcus (Fig. 10). A transverse sternacostal sulcus bisects the ventral plate and thereby forms an anterior basisternite and posterior furcasternite (Fig. 10). The basisternite (basisternum) is the primary sclerite of the sternum (Fig. 10). It is positioned anterior to the sternal apophyses or sternacostal suture and laterally connected with the pleural region of the precoxal bridge. The furcasternite (furcasternum) is a distinct part of the sternum in some insects bearing the furca (Fig. 10). The spinasternum is a "spine-bearing" intersegmental sclerite of the thoracic venter, associated or united with the preceding sternum. The spinasternum may become part of the definitive prosternum or mesosternum, but not of the metasternum. The sternellum is the second sclerite of the ventral part of each thoracic segment, frequently divided into longitudinal parts that may be widely separated (Figs. 7, 10).

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