Reassessment of Morphological Diagnostic Characters and Species Boundaries Requires Taxonomical Changes for the Genus Orthopyxis L. Agassiz, 1862 (Campanulariidae, Hydrozoa) and Some Related Campanulariids

Abstract

The genus Orthopyxis is widely known for its morphological variability, making species identification particularly difficult. A number of nominal species have been recorded in the southwestern Atlantic, although most of these records are doubtful. The goal of this study was to infer species boundaries in the genus Orthopyxis from the southwestern Atlantic using an integrative approach. Intergeneric limits were also tested using comparisons with specimens of the genus Campanularia. We performed DNA analyses using the mitochondrial genes 16S and COI and the nuclear ITS1 and ITS2 regions. Orthopyxis was monophyletic in maximum likelihood analyses using the combined dataset and in analyses with 16S alone. Four lineages of Orthopyxis were retrieved for all analyses, corresponding morphologically to the species Orthopyxis sargassicola (previously known in the area), Orthopyxis crenata (first recorded for the southwestern Atlantic), Orthopyxis caliculata (= Orthopyxis minuta Vannucci, 1949 and considered a synonym of O. integra by some authors), and Orthopyxis mianzani sp. nov. A re-evaluation of the traditional morphological diagnostic characters, guided by our molecular analyses, revealed that O. integra does not occur in the study area, and O. caliculata is the correct identification of one of the lineages occurring in this region, corroborating the validity of that species. Orthopyxis mianzani sp. nov. resembles O. caliculata with respect to gonothecae morphology and a smooth hydrothecae rim, although it shows significant differences for other characters, such as perisarc thickness, which has traditionally been thought to have wide intraspecific variation. The species O. sargassicola is morphologically similar to O. crenata, although they differ in gonothecae morphology, and these species can only be reliably identified when this structure is present.

Faunal assemblages of intertidal hydroids (Hydrozoa, Cnidaria) from Argentinean Patagonia (Southwestern Atlantic Ocean)

“…Cunha et al, 2015). The use of stems of hydroids as substrata for other hydroid species is also a common phenomenon for the temperate southwestern Atlantic (e.g., stems of Amphisbetia operculata, Plumularia setacea; Genzano, 1994;Genzano et al, 2009;Meretta & Genzano, 2015).…”

“…Previous knowledge for the hydroids of the area is concentrated in subtidal waters either as faunal components within an ecological study (Schwindt et al, 2014) or as a source of taxonomical information from shelf areas (Vervoort, 1972;Stepanjants, 1979;Genzano et al, 1991;Blanco, 1994;El Beshbeeshy & Jarms, 2011). The majority of the Patagonian records for hydroid species are still from occasional and scattered faunal surveys (see Blanco, 1994, and references therein) and from specific taxonomic studies (Rodriguez et al, 2012;Cunha et al, 2015).…”

Areas of endemism in the Southwestern Atlantic Ocean based on the distribution of benthic hydroids (Cnidaria: Hydrozoa)

“…This was strictly necessary because the taxonomic history of Hydrozoa is complicated. The group contains a large number of taxa with intraspecific variation and countless taxonomic issues, involving different life cycle strategies and the consequences of the long time use of a dual classification system for polyps and medusae (Cornelius 1982(Cornelius , 1990Calder 1988;Cunha et al 2015;Gravili et al 2015). Since then, many phylogenetic classifications for the more inclusive taxa of Hydrozoa were proposed (Collins 2000(Collins , 2002Marques 2001;Marques & Collins 2004;Collins et al 2005Collins et al , 2006Collins et al , 2008Cartwright et al 2008;Leclère et al 2009;Cartwright & Nawrocki 2010;Nawrocki et al 2010).…”

“…Considering the high complexity of Hydrozoa's taxonomy, we preferred to personally review in detail our primary data for the SWAO. We based our taxonomic conclusions on records published exclusively for this area (viz., Genzano et al 2009;Cunha et al 2015), to guarantee the taxonomic accuracy of the dataset and to avoid possible taxonomic and geographic biases.…”

Padrões de diversificação de Bougainvilliidae no contexto evolutivo de Medusozoa (Cnidaria)

“…Consequently, this structural variation may lead to misidentifications of the species, especially when other diagnostic characters are absent (e.g., reproductive structures), and should not be used as diagnostic characters for the taxonomy of groups such as Pandeidae and Bougainvilliidae . Nevertheless, the variation in thickness of the chitin-protein exoskeleton is considered a useful diagnostic character for some families of Leptothecata (e.g., Campanulariidae, Cunha et al, 2015).…”