"Как известно любому зоологу, реальная организация тела членистоногих сильно отличается от архетипической модели серии сегментных модулей, организованных в специализированные группы, тагмы. Однако очевидность этого наблюдения может позволить упустить из виду, что идеализированные концепции могут подсознательно проникнуть в текущие исследования.
Сегменты, как модульные части основной оси тела, не являются неизбежными продуктами сегментарной организации многих различных морфологических структур, а тагмы не являются неизбежными продуктами региональной специализации сегментарных структур. Сегменты и тагмы в некоторой степени эпифеноменальны, они возникают при выполнении определенных, хотя и нередких, условий для сегментации и серийной специализации."




9.6 Final Remarks
As any zoologist knows, the actual body organization of arthropods is quite different from the archetypical model of a series of segmental modules organized in specialized groups that form the tagmata. The obviousness of this observation, however, can make it easy to overlook, to the point that idealized conceptions can subliminally creep into current investigations.
Segments, as modular partitions of the main body axis, are not inescapable products of the segmental organization of many different morphological structures, and tagmata are not unavoidable products of regional specializations of segmental structures. Segments and tagmata are to some extent epiphenomenal, emerging when particular, although not infrequent, conditions for segmentation and serial specialization are met. For instance, in cases of periodic concordance between several segmental structures (e.g., the series of leg pairs, tergites, sternites, spiracles, neuromers), the body can quite realistically be described as comprised of a certain number of segments, that is, modular partitions of the main body axis (Minelli and Fusco 2004).
Otherwise, when many different segmental structures show discordant arrangement, segment delimitation and count should be acknowledged as at least arbitrary, if not questionably meaningful.
Segments and tagmata certainly have a fundamental role in descriptions and comparisons, but their value as developmental units or units of evolutionary change should not be uncritically assumed. With some attention, it is possible to exploit the undisputable descriptive value of segments and tagmata without falling in the trap of envisaging constraints to arthropod phenotypic evolution based on the limits posed by the evolution of these modules. In such a case, a morphological description of body units would be mistaken for a sort of ‘internal description’ (e.g., Lawrence 1992) of the animal capable of constraining evolutionary changes of body organization. Even conceding the existence of such units of internal description (see Fusco 2008 for an argument against), these do not necessarily match with the units we can detect by inspecting external morphology, internal anatomy or gene expression.

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