Rocinela signata Schioedte and Meinert, 1879

Rocinela signata Schioedte and Meinert, 1879 View in CoL

( Fig. 5 View Figure 5 )

Material examined. Mazatlán Bay, Mar. 3, 2023, 1 female (TL 4.6), gills of Lutjanus argentiventris ( Lutjanidae ) (EMU 13780); 2 females (TL7–10), gills of H. guentherii . Sep. 20, 2023, 2 females (TL10.4– 11.4), gills of H. guentherii . Nov. 4, 2023, 1 female (TL 15.3), gills Eucinostomus currani ( Gerridae ). Nov. 8, 2023, 1 female (T.L. 13.1), gills Balistes polylepis ( Balistidae ).

Distribution. California, U.S.A., to Ecuador and

Galapagos Islands ( Brusca and France, 1992).

Previous known hosts. In the Eastern Pacific, Anisotremus interruptus ( Haemulidae ), Mycteroperca jordani ( Serranidae ), Parapsettus panamensis ( Ephippidae ), Euthynnus lineatus ( Scombridae ), Scomberomorus sierra ( Scombridae ), Caranx sexfasciatus , Caranx caninus , Caranx caballus , Caranx vinctus , Chloroscombrus orqueta , S. peruviana , Hemicaranx leucurus ( Carangidae ), H. guentherii and L. guttatus ( Lutjanidae ) ( Brusca and France, 1992; Miranda-Delgado et al., 2019; Santos-Bustos et al., 2020a; Violante-González et al., 2016; 2020; Villalba et al., 2022; Osuna-Cabanillas et al.,2024).

Remarks. According to Brusca and France (1992), Ro.signata can be distinguished from the other species of Rocinela by having a long medial process of the uropodal peduncle (more than 70% of the uropod length), distal margin of pereonites smooth, and the propod of pereopods I–III not medially expanded with only 1 or 2 minute spiniform setae. Another character considered reliable for the identification of R. signata is the presence of a chromatophore pattern similar to an inverted “W” on the dorsum of the pleotelson ( Moreira, 1972; Cardoso et al., 2017; Aguilar-Perera and Noh-Quiñonez, 2022). The specimens we sampled correspond with the description of Ro. signata given by Brusca and France (1992), however, only two of the six specimens of our study had a “W”-like pattern of chromatophores on the pleotelson ( Fig. 5b View Figure 5 ). Brusca and France (1992) had already pointed out that the chromatophore pattern was not constant among nearly 60 of the specimens from the Eastern Pacific they observed. Moreover, if the presence of Ro. signata in the Eastern Pacific is not the result of its introduction in relatively recent times, its amphi-American distribution is, at least, suspicious. In this context, Baddour et al. (2024) refer to a case of parasitism of Ro. signata on Fistularia commersonii ( Fistulariidae ) in Syria although they support their identification with a poor description and the presence of an inverted “W” in the pleotelson of the isopods. We cannot rule out that the presence of “ Ro. signata ” in Syria was a case of an introduction of the species in that region, but we consider that a key identification of this species based on the pigmentation of the pleotelson could be erroneous. The variations in the body parts and chromatophore patterns of the specimens reported as Ro. signata lead us to think that the wide distribution of this species could represent a species complex. A detailed study and the comparison of individuals from different populations, based on both, morphological and molecular analysis, is desirable to assess the taxonomic status of this species.