Ultrastructure of the ventral pharynx in the interstitial annelid Questa paucibranchiata (Orbiniidae) and its phylogenetic significance

The small taxon Questa comprises only meiofaunal species and shows oligochaete-like adaptations in its reproductive biology. Formerly, it was classified as a separate polychaete group, Questidae, of uncertain affinities, but due to these oligochaete-like similarities, a relationship with Clitellata...

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Bibliographic Details
Published in:Zoomorphology 2011-09, Vol.130 (3), p.167-180
Main Authors: Beermann, Arne, Giere, Olav, Purschke, Günter
Format: Article
Language:English
Subjects:
Adaptation
Animal Anatomy
Animal Systematics/Taxonomy/Biogeography
Biology
Biomedical and Life Sciences
Capillaries
Developmental Biology
Evolutionary Biology
Histology
Hooks
Interstitial cells
Interstitial environment
Life Sciences
Morphology
Orbiniidae
Original Paper
Pharynx
Phylogenetics
Phylogeny
Ultrastructure
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Summary:The small taxon Questa comprises only meiofaunal species and shows oligochaete-like adaptations in its reproductive biology. Formerly, it was classified as a separate polychaete group, Questidae, of uncertain affinities, but due to these oligochaete-like similarities, a relationship with Clitellata was discussed. However, other morphological phylogenetic analyses questioned such a relationship, providing evidence for common ancestry with Paraonidae and Orbiniidae. Molecular studies revealed that questids even form an in-group of Orbiniidae, which refutes a clitellate relationship without doubt. On the other hand, morphological evidence supporting this grouping is still considered weak. Among the external characters, the chaetation, comprising crenulated capillaries, hooks and furcate chaetae, might strengthen this hypothesis. One of the internal characters stated to support this grouping is the ventral pharynx, which as such, however, is widespread among polychaetes. This study is a first attempt to look for specific structures in this organ, which might be regarded as synapomorphic of Questa and Orbiniidae. The ultrastructural analysis revealed a ventral buccal organ composed of large interstitial cells and transverse muscle fibres and surrounded by an investing muscle system similar to that found in juvenile Orbiniidae. Thus, further morphological evidence for the current position is provided. Moreover, since this structure is known as a larval or juvenile character in Orbiniidae, this finding is also indicative for a progenetic origin of Questa , which might have occurred upon invading the interstitial environment.
ISSN:0720-213X
1432-234X
DOI:10.1007/s00435-011-0129-9