Tsalolikhin S.J. 2006. [The evolution of the supplementary apparatus in tobrilids (Nematoda: Enoplida, Tobrilidae)] // Invertebrate Zoology. Vol.3. No.1: 41–51 [in Russian, with English summary].
Zoological Institute, Russian Academy of Sciences, St. Petersburg 199034, Russia. E-mail: email@example.com
KEY WORDS: Nematodes, Tobrilidae, supplementary apparatus, oligomerisation.
ABSTRACT: The evolution of the supplementary apparatus in tobrilid nematodes is directed towards a decline in the number of supplements and intensification of their functions (in accordance with Dogiel’s principle of oligomerization of homologous organs). As a result of this process an optimum ratio is established between the capture ring of the male, which is formed at the moment of copulation (when the male winds the precloacal part of its body with the supplements around the female) and the circumference of the female body in the region of the vulva. This ratio (coefficient ♂/♀) for the family is on the average 1.18 ± 0.06. The lower tobrilids have more than 6 supplements. The process of oligomerization occurs due to reduction of one of the middle supplements. In the higher tobrilids the normal number of supplements is constant and nearly always equals 6. As an exception there are species with 5 supplements, e.g. Epitobrilus medius. In the process of the evolution the reduction of the last weakly developed supplement 6 can be observed, e. g. in E. andrassyi. The supplementary row remains non-oligomerized in those species where there are fewer males than females. Analyzing the value of the coefficient ♂/♀ one should take into account the notable polymorphism of the populations of the majority of tobrilid species.