We present a detailed morphological description and a DNA barcoding of Parabrachiella
platensis n. sp. collected from Mugil liza Valenciennes in Samborombon Bay (Buenos
Aires, Argentina). This new species was compared with two Parabrachiella species parasitic
on mugilids: Parabrachiella exilis (Shiino, 1956) and Parabrachiella mugilis (Kabata,
Raibaut et Ben Hassine, 1971). Parabrachiella platensis n. sp. differs from those
species in the shape of posterior processes, the anal slit with two pairs of bipartite
papillae, the size of cephalothorax, the trunk, the maxilla, the microhabitat on the
host, and the lack of caudal rami. On the host, the new species was in the nostrils
(a new site for a species of the genus Parabrachiella) and in the fins base. Some
minor morphological differences were observed in relation to the locations on the
host. The molecular analysis conducted based on mtDNA-COI between specimens of the
new species on the fins and nostrils showed a genetic similarity of 99.8%. This percentage
supports that the specimens found in nostrils and fins base could represent a single
species. New studies on P. platensis n. sp., including infection of the same fish
with the two forms, could bring some new information. Anyway according to the genetic
information provided and the minimal morphological differences spotted we conclude
that the two forms are a single specie. The differences observed are possibly influenced
by the place of the host where the two forms of copepods were found, nostrils and
fins. The new species was also molecularly compared to other five species of Parabrachiella
including P. exilis (parasitizing mugilid from Chile), Parabrachiella anisotremis,
Parabrachiella auriculata, Parabrachiella merluccii, and P. hugu (the last two sequences
were taken from the GenBank). The genetic distance of 9% among P. platensis n. sp.
and P. exilis, which is the close morphological related species, allow to states that
these two copepods on mugilids belong to different species and then validating the
morphological differences found between them.