The morphology and possible origin of the hemipteran loral lobes

Publisher Website
Google Scholar
Abstract
The loral lobes of the hemipteran cranium are described and their possible homologies are discussed. It is proposed that the hemipteran head arose from a hypothetical first stage which had many generalized pterygote characteristics, including the lack of a prepharynx. From this initial stage, a head with a prepharynx, a functional [as apposed to morphological) mouth, and loral lobes could have developed in at least three ways, each of which assumes a different interpretation of the loral lobes.Of the three theories discussed here, the hypopharyngeal one is, in my opinion, the most satisfactory, and the clypeal one the least. Although the clypeal theory is the only one of the three which is strongly supported by embryological evidence, it can also be more strongly criticized than the other two. Major drawbacks are (1) its complexity, (2) its interpretation of the functional mouth, and (3) the fact that it is inconsistent with the innervation of the loral lobes and with their condition in the Hydrocorisae.Supporters of the genal–subgenal theory cite the sternal origin of the hypopharynx as a major objection to the hypopharyngeal theory. This rather questionable criticism is, in my estimation, more than compensated for by the drawbacks of the genal–subgenal theory which include (1) its relative complexity, (2) the lack of any definite embryological evidence for it. and, perhaps most serious, (3) its interpretation of the loromaxillary cleft as an intersegmental boundary.The hypopharyngeal theory has none of the drawbacks of the other two except the lack of conclusive embryological evidence. It is the simplest of the three theories, explains both the typical morphology of the loral lobes and their modification in the Hydrocorisae. and is consistent with the generally accepted views of the phylogeny of the Heteroptera.

This publication has 0 references indexed in Scilit: