1974] 
Parsons & Hewson — Cryphocricos 
51 1 
exoskeleton is quite thick, and the relatively large size of the insect 
( C . hungerfordi is 8. 5-9.5 mm long; C. barozzii is 10-13 mm long) 
produces an unfavorable ratio of volume to surface area. 
Among the aquatic Heteroptera, true plastral respiration has thus 
far been experimentally demonstrated only in Aphelocheirus (Thorpe 
and Crisp 1947a, 1947b; Thorpe 1950). Whether this insect is a 
naucorid (Usinger 1956) or represents a separate family, the Aphelo- 
cheiridae (Parsons 1969) is debatable. Aphelocheirus possesses a 
very thin, permanent air layer, or “plastron”, which is retained by 
short, densely-packed hairs on most of the dorsal and ventral surfaces 
of the body. The plastron is exposed to the water and acts as a gill, 
obtaining enough dissolved oxygen from the water to make the in- 
sect independent of atmospheric oxygen (Thorpe and Crisp 1947a; 
Thorpe 1950). Cryphocricos and Aphelocheirus share such morpho- 
logical similarities as reduced forewings, vestigial hindwings, lack of 
a large air store, and paired abdominal pressure receptors of a type 
not yet reported in any other Heteroptera ( Aphelocheirus , Thorpe 
and Crisp 1947c, Larsen 1955; Cryphocricos , Thorpe 1950, Parsons 
1974). These similarities suggest that Cryphocricos , like Aphelo- 
cheirus, has a plastral type of respiration. Hinton (1969a, p. 198) 
has remarked that “Por ejemplo, entre insectos adultos hay por lo 
menos cuatro origenes independientes de respiracion de plastron den- 
tro de la familia Naucoridae: Aphelocheirus , Cryphocricos , Heleo- 
coris, e Idiocarus” . He included a photomicrograph of thoracic 
plastral hairs in Heleocoris but did not further elaborate on his 
statement. 
Although the presence of plastral respiration would be best dem- 
onstrated by both morphological and physiological studies, live speci- 
mens of Cryphocricos were not available for experimentation. Our 
investigation, like Hinton’s (1969b) study on aquatic beetles, was 
therefore confined to morphology. Its purposes were ( 1 ) to discover 
whether the exposed surfaces of the body possess hydrofuge devices 
which might retain a thin plastral air layer, and (2) briefly to com- 
pare any such structures with those of other insects in which plastral 
respiration is believed to occur. 
Materials and Methods 
Species used : 
Cryphocricos barozzii Signoret (preserved in formalin; collected 
in Brazil by F. Plaumann; two specimens) 
C. hungerfordi Usinger (preserved in alcohol; collected in Mexico 
by J. T. Polhemus ; one specimen ) 
