Taking into account the difficulties of taxonomic identification of larval anisakid nematodes based on morphological
characters, genetic analyses were performed, together with those usually applied, in order to identify
anisakid larvae found in the flounder
Paralichthys isosceles
from the littoral of the state of Rio de Janeiro, Brazil.
The analysis of 1,820 larvae revealed a new species, similar to
Hysterothylacium MD,
Hysterothylacium 2,
Hysterothylacium
KB and
Hysterothylacium sp regarding the absence of the larval tooth, an excretory pore situated
below the nerve ring level, and slender lateral alae. Moreover, the new species differs from
Hysterothylacium fortalezae
and
Hysterothylacium reliquens
with regard to the number and size of spines present on the tail end and
from
Hysterothylacium patagonicus
by the absence of interlabia. The maximum parsimony and neighbour joining
tree topologies based on the 18S ribosomal DNA gene, complete internal transcribed spacer region and cytochrome
oxidase 2 (COII) gene demonstrated that the Brazilian larvae belong to Raphidascarididae and represent a unique
genetic entity, confirmed as a new
Hysterothylacium species. Furthermore, the new species presents COII genetic
signatures and shares polymorphisms with Raphidascarididae members. This is the first description of a new anisakid
species from Brazil through the integration of morphological and molecular taxonomy data.
