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Medical imagery and plastination: Tools for understanding flatfish phylogeny (Pleuronectiformes)

By Cyril - Posted on 17 April 2014

TitleMedical imagery and plastination: Tools for understanding flatfish phylogeny (Pleuronectiformes)
Publication TypeMiscellaneous
Year of Publication2007
AuthorsChanet B, Desoutter M, Guintard C
AbstractThe study of flatfish interrelationships has been mainly a bony story. Most features used to reconstruct the phylogeny of pleuronectiform fishes are up to now skeleton structures features. Nevertheless, some dissections and a survey of the literature showed that the study of soft anatomy reveals an amount of data, which are worthy of interest to understand better flatfish phylogenetics. Four features have been examined: 1. presence of digestive appendages, 2. posterior extension of digestive tract, 3. presence of an asymmetrical kidney lobe, 4. structure of the optic chiasma. The absence of pyloric appendages (1) appears to be a synapomorphy of the clade formed by Poecilopsettidae,. Rhombosoleidae, Samaridae, Achiridae, Soleidae and Cynoglossidae, with convergences with derived genera of Pleuronectidae and Scophthalmidae. The posterior extension of the digestive tract (2) seems to be an evolved character-state shared by Achiridae and Soleidae. An asymmetric kidney caudal lobe (3) is present in the species belonging to Achiridae-Soleidae-Cynoglossidae clade. A monomorphic optic chiasma (4) may be an evolved character-state for flatfishes of the citharid family and the bothoid group, while the dimorphic optic chiasma present in Achiridae, Soleidae and Cynoglossidae would be the result of a reversion. Even if more dissections and observations are needed to corroborate or refute these hypotheses, the present analysis shows that soft anatomy features can provide phylogenetic information. Nevertheless, this kind of study is not easy to perform, especially on preserved specimens. Both museologic and practical reasons prevent to make a large number of dissections: preserved tissues are hard to dissect and curators hesitate before committing destructive acts on collection specimens. To avoid these problems, we have tried to use modern medical imagery techniques (High resolution echography, Magnetic Resonance Imaging, etc.) on alcohol-preserved specimens. These techniques provide data without destroying specimens, but the reading and the interpretation of the obtained images need a long teaching step. Meanwhile, the Magnetic Resonance Imaging technique (MRI) seems to be the most efficient one to obtain data, but a high intensity magnetic field is needed to observe anatomical details. Anyway, theses approaches do not replace dissections, which are still useful to learn, teach and discover anatomy. In that perspective, the technique of plastination appears to be a good mean to preserve dissected specimens.