Meeting Abstract

S2.7  Sunday, Jan. 4  Branchiura, -parasitic crustaceans with a sting MOELLER, O. S.; University of Rostock ole.moeller@uni-rostock.de

The Branchiura are fascinating parasitic crustaceans not only able to attach to the slippery sides of freshwater fish, but also able to detach at will and swim freely to find another host. The Branchiura display two different ways of attachment to the fish surface as adults: the Mx1s are either hooks (Dolops) or suction discs (Argulus, Chonopeltis, and Dipteropeltis). In larval A. foliaceus the first maxillae are hooks. During larval development, the proximal part of the first maxilla increases in size to form a large disc/cup. Specific homologies exist between the larval hooks of Argulus and the adult hooks of Do. ranarum: The Mx1 distal segment terminating in a double structure: a distal two-part hook (in Argulus) or one hook and an associate spine-like structure (in Dolops). In the phylogenetic reconstruction based on mt16S rRNA, 18S and 28S rRNA), Do. ranarum is found to be a sister group to all other Branchiura, which here comprise six Argulus and one Chonopeltis species. Based on the molecular phylogeny a likely evolutionary scenario is that the ancestral branchiuran used hooks for attachment, as seen in Dolops, of which the proximal part was then modified into suction discs in Argulus and Chonopeltis (and Dipteropeltis). Based on previously overlooked papers and a re-investigation of paratype material, the presence of a pre-oral spine in D. hirundo was finally confirmed. As this character could possibly support a Argulus+Dipteropeltis clade and the molecular data suggest Argulus as paraphyletic with respect to Chonopeltis, (no Dipteropeltis seqs are available), the internal topology of the branchiuran genera remains open. Our phylogenetic reconstructions confirm the sister group relationship of the Branchiura and Pentastomida with the most comprehensive taxon sampling until now. No evidence supports a branchiuran in-group position of the Pentastomida.