MODIFICATION OF THE 
INTERSEGMENTAL REGION IN THE 
PTEROTHORAX OF CRYPHOCRICOS 
(HETEROPTERA: NAUCORIDAE ) * 
By Margaret C. Parsons 
Department of Zoology, University of Toronto 
Toronto, Ontario M5S 1A1 
Introduction 
In most Hydrocorisae (aquatic Heteroptera) the hindlegs are used 
for swimming, and their extrinsic muscles, which originate in the 
metathorax, are well developed. The tergal and pleural depressors 
of the metathoracic trochanter (Muscles 70 and 71, respectively, of 
Larsen, 1945) are especially large in many Hydrocorisae, including 
the Naucoridae (Larsen, 1945) and the closely related family 
Aphelocheiridae (Parsons, 1969). These muscles slant anterolaterally 
in the metathorax, their anteriormost fibers originating near its 
boundary with the mesothorax. 
In at least three genera of Naucoridae ( Limnocoris , Ambrysus, 
and Cryphocricos) the anterior part of the metathoracic episternum, 
on which Muscle 71 originates, usually projects into the cavity of 
the preceding segment. This makes it appear, at first glance, that 
the anteriormost fibers of the muscle attach on the mesothorax. The 
metapleural projection, which will be described in a later publication, 
appears to be produced by post-ecdysial growth of the skeleton, since 
it is absent in newly-moulted adults and is present only in older ones. 
Another example of post-ecdysial skeletal change occurs in the 
tergum of adult Cryphocricos barozzii and makes the anteriormost 
fibers of Muscle 70 appear to originate on the mesothorax rather 
than on the metathorax. This tergal modification seems to occur only 
in micropterous specimens, with reduced forewings. I have not ob- 
served it in macropterous Cryphocricos or in Ambrysus , Limnocoris , 
or Pelocoris, all of which possess forewings of normal length. 
Materials and Methods 
Cryphocricos barozzii Signoret, collected in Nova Teutonia, Brazil, 
and preserved in 70% alcohol, were dissected in 80% alcohol under 
* Manuscript received by the editor January 20, 1974. 
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