Description of a new species of Marionia (Gastropoda: Heterobranchia: Tritoniidae) from the Gulf of Guinea (eastern Atlantic Ocean)

Abstract

A new species of dendronotid nudibranch, Marionia abrahamorum sp. nov., is described here. This species was found on Príncipe Island (Gulf of Guinea, eastern Atlantic Ocean), and its description is based on its morphological characteristics as well as molecular data from two mitochondrial (cytochrome c oxidase subunit I and 16S rRNA) markers and one nuclear (histone-3) marker. This species differs from all known Tritoniidae in terms of its size, color pattern, notum pattern, number of velar processes, number of gills, presence of stomach plates, and radular formula. The phylogenetic results support the results of the morphological analysis, confirming its placement within the genus Marionia. Sea slugs from the family Tritoniidae (Nudibranchia, Cladobranchia, Dendronotidae) span a variety of sizes and colors, but they feed exclusively on octocorals (McDonald and Nybakken 1999). The eight currently valid genera are Tritonia,

Consolidated data on the phylogeny and evolution of the family Tritoniidae (Gastropoda: Nudibranchia) contribute to genera reassessment and clarify the taxonomic status of the neuroscience models Tritonia and Tochuina

“…Importantly, according to all available data Marionia invariably forms a separate clade from other tritoniids [5,19,72,92; present study, Fig 1A]. Therefore, potentially Marionia with related genera Marioniopsis and Paratritonia (and more genera which have to be separated) should be placed in a separate family.…”

“…However it will require special explanation because considerable ontogenetic similarities between radulae of Dendronotidae and Tritoniidae [78,79] contradict to the paraphyly of traditional dendronotaceans. The unstable phylogenetic position of the tritoniid Marionia (with distinct branched appendages) either basal to all tritoniids [19, present study] or rendering Tritoniidae paraphyletic [5,72,92] also does not support this scenario. The tracing of the dorsolateral appendages and secondary gills evolution is therefore important both for the family Tritoniidae phylogeny and for a broadscope understanding of the evolutionary pathways among nudibranch molluscs.…”

“…Tochuina are sometimes omitted [19] in spite of the current valid status [71]. The genus Marionia Vayssière, 1877 is different from other tritoniid taxa because of presence of stomach plates, but otherwise contains numerous species with disparate morphology, and molecular phylogenetic data show within Marionia at least two distinct clades [5,72]. The taxonomy of the type tritoniid genus Tritonia has been especially controversial.…”

“…In this connection, there is another considerable issue with the genus Marionia that affects all tritoniids. The majority of the available phylogenetic analyses [5,72,92] Table 3.…”