New insights on Pomphorhynchus sphaericus Gil de Pertierra, Spatz et Doma, 1996 (Acanthocephala: Pomphorhynchidae)

The finding of Pomphorhynchus sphaericus in new localities from La Plata River allowed the reevaluation of the species using a taxonomic integrative approach. The newly found specimens in Pimelodus maculatus from Samborombon Bay differ from P. sphaericus by the roots of hooks 1-6 which not form a wide sheet split into 2 apophysis, the slender, separated and equatorial testicles, the position of the cement glands, the shape of the proboscis, the shape and length of lemnisci, and the eggs size. Despite the notorious observed morphological differences, the COI mtDNA analysis confirmed that Pomphorhynchus individuals are the same conspecific, and showed that there is a high phenotypical plasticity in this species. Pomphorhynchus sphaericus is the first South American species analyzed to a DNA level (COI mtDNA, ITS, and 18S rDNA genes). The molecular analysis relates P. sphaericus to P. bulbocolli and P. purhepechus.