Sur l'intérêt et l'actualité de l'étude anatomique l'exemple des Gastrotriches Macrodasyoïdes
| Main Author: | d'Hondt |
|---|---|
| Format: | Article |
| Bahasa: | fra |
| Terbitan: |
, 2017
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| Subjects: | |
| Online Access: |
https://zenodo.org/record/1098283 |
Daftar Isi:
- The genital anatomies of males and females present, in each of the families of macrodasyoid Gastrotricha, a distinctive and ontogenetically programmed arrangement. However, within each of these families there are modulations of the same organizational plan that have, amongst other characters, been used by sytematicists to delimit genera, these consisting of the form, presence/absence, location, complexity or relative dimensions of a given accessory organ, the direction of egg growth and the number of gonads. In some cases, the variability of these characteristics already determines criteria of interspecific rank, meaning at the lower level of the Linnean classification. This concerns the structure of accessory organs, their correlation with the male genital pores, the localization of the latter, the atrophy of gonads or canals, which sometimes allows the reconstruction of evolutionary series, and the presence/absence of a copulatory organ. Discontinuities in the evolution of a character within a lineage in certain cases – those that are most conspicuous and in the absence of anatomically intermediate taxa – determine the gaps used by systematicians to delimit taxa. Because a given character does not necessarily have the same significance or importance according to the macrodasyoid line concerned, the diversity (and sometimes the mosaic) of the resulting situations makes it possible to assign, according to the taxa, the respective and “weights” and significance of these characters, and hence the limits of validity of these criteria according to the taxa. Depending on the family in macrodasyoids, the presence or form of an anatomical genital character can either be a shared character defining a lineage of species, or else just a specific character. In the first case, the shared character might enter into the definition of a supraspecific taxon (e.g. a genus, to which it would be unique) and correspond to a systematic character. In the second case, the presence or form of the character might be subject to variations from its initial form, which would allow the species concerned to be integrated into an evolutionary series and permit a phylogenetic interpretation. In cases where these species are distributed along the length of a single evolutionary line, those occupying the two ends of the “chain” could, when considered separately, have been classified a priori in different genera, hence it is the existence of intermediate taxa that justifies the unity of the group. In other cases, the absence of intermediate species between two taxa with different states of the same character justifies their separation. Finally, some species have had their genitalia insufficiently described for them to be objectively classified in one genus rather than another that is morphologically close. In such cases it would be more objective to treat them as species incertae sedis, rather than placing them in “oversized” and heterogeneous genera – an unsatisfactory situation that leads to the blurring of the meaning of a diagnostic character. Although the aim of systematics is precisely to organize and hierarchize our knowledge, this sometimes raises ethical problems. The genus Kienekella gen. nov. is described.