Marioniopsis Odhner 1934

Silva, Felipe De Vasconcelos, Pola, Marta & Cervera, Juan Lucas, 2023, A stomach plate to divide them all: a phylogenetic reassessment of the family Tritoniidae (Nudibranchia: Cladobranchia), Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 199 (2), pp. 445-476 : 471

Genus Marioniopsis Odhner 1934 ( Fig. 3K )

Type species: Marioniopsis cyanobranchiata (Rüppell and Leuckart 1828) , by original designation.

Diagnosis: Rachidian tooth tricuspid, denticulate. Masticatory border denticulate, denticles blunt or rod-shaped. Digestive system arrangement cladohepatic or holohepatic, not U- or G-shaped.

Morphology: Body slender or broad, length up to 88 mm ( Fig. 3K ). Oral veil bilobed. Three to seven simple or branched velar processes, with the outermost ones oħen longer. Fully arborescent gills with at least seven pairs. Rachidian tooth tricuspid and denticulate (with accessory denticles or folds). Masticatory border of the jaws denticulate, with large-sized (up to 300 µm) denticles with conical bases and blunt cusps or rod-shaped denticles. ODG complex clado- or holohepatic arrangement, with the stomach located in the central or right region of the posterior ODG complex (cladohepatic) or posterior ODG complex portion/lobe (holohepatic arrangement). Penis flagelliform, cylindrical or conical.

Species composition: Marioniopsis albotuberculata Eliot 1904 , Marioniopsis arborescens , Marioniopsis bathycarolinensis (V.G. Smith and Gosliner 2005) comb. nov., Marioniopsis cyanobranchiata , Marioniopsis elongoreticulata comb. nov., Marioniopsis elongoviridis comb. nov., Marioniopsis hawaiiensis comb. nov., Marioniopsis levis , Marioniopsis pellucida Eliot 1904 , Marioniopsis ramosa ( Eliot 1904) comb. nov., Marioniopsis tedi (Ev. Marcus 1983) comb. nov. and Marioniopsis viridescens Eliot 1904

Remarks: The genus Marioniopsis , originally created to assign plate-bearing tritoniids with holohepatic digestive systems and a single row of denticulate masticatory border of the jaw ( Odhner 1936), was synonymized with Marionia due to taxonomic uncertainties regarding the validity of its morphological characters ( Smith and Gosliner 2005). Based on our phylogenetic analyses, the genus Marioniopsis is reinstated here to assign the plate-bearing species recovered clustered as the sister clade of Marionia ( Fig. 2 ).

The synapomorphies of Marioniopsis within Marioniinae are the denticulate rachidian tooth and blunt and rounded or rod-shaped denticles in the masticatory border. In addition, Marioniopsis has both holohepatic and cladohepatic arrangements, which lack a U- or G-shape, unlike Marionia , which has only a cladohepatic arrangement. However, the distinction between cladohepatic and holohepatic arrangements can be tricky. For example, the fusion of the right and leħ lobes of the ODG complex in Marioniopsis arborescens and Marioniopsis levis was initially overlooked in their original descriptions (Rüppell and Leuckart 1828, Eliot 1904) and only noticed later when Marioniopsis was originally proposed ( Odhner 1936).

Species currently assigned to Marionia for which no molecular data are available, namely Marionia albotuberculata , Marionia bathycarolinensis , Marionia cyanobranchiata , Marionia pelucida , Marionia tedi , Marionia ramosa and Marionia viridescens , were transferred to Marioniopsis in this study based on their denticulate rachidian tooth, denticulate masticatory border of the jaw, presence of true stomach plates and cladohepatic (in Marionia tedi ) or holohepatic ODG complex ( Eliot 1904, Ev. Marcus 1983, Smith and Gosliner 2005). Not surprisingly, most of these species have been included in Marioniopsis in the past due to their holohepatic ODG complex and, therefore, are not considered combinatio nova in this study. We have not included species previously assigned to Marioniopsis that did not fit our proposed diagnosis and lack of molecular data, such as the divergent Marionia platyctenea ( Willan 1988) . In addition, Marioniopsis has a high minimum COI interspecific p -distance, peaking at 22.5% (Table 3), suggesting the presence of other generic lineages within the genus. Once the various unnamed species are formally described, their internal and external morphology may reveal new characters for further delimitation at the generic level.

Figures

Figure 2. Bayesian phylogenetic tree based on the concatenated molecular data (COI + 16S + H3) of Tritoniidae (sensu Odhner 1963). Outgroup taxa are depicted in grey.Tritoniidae genera are independently coloured, and branches with several replicates for each species hypothesis were collapsed for clarity.Names in bold are species which sequences were generated for this study with the number of sequenced specimens showed in brackets. PP are shown right/top and BS leħ/boưom.Unsupported branches are not labelled. Green circles indicate maximum support by both analyses. Solid vertical bars indicate specimens grouped as species entities based on COI dataset. Empty vertical bars indicate the specimens grouped as species based on the 16S dataset.

Figure 3. Representative species of genera of Tritoniidae (with exception of Paratritonia). A, Tritonia hombergii (MNCN15.05/93379) (Portaferry, Ireland); B, Candiella plebeia (MNCN15.05/93393) (Portaferry, Ireland); C, Tritoniopsis elegans (MB28-0045061) (Zavora, Mozambique); D, Tritonidoxa capensis (MNCN15.05/93399) (Scoưburg, South Africa); E, Tritoniella belli (Antarctica); F, Marianina rosea (French Polynesia); G, Myrella challengeriana comb.nov.(Bahía Camarones, Argentina); H, Tochuina gigantea (Agnew Pass, USA); I, Tritonicula khaleesi (MZUSP113165) (Fortaleza, Brazil); J, Marionia cucullata (Golfo Nuevo, Argentina); (K) Marioniopsis levis ‘1’ (MNHNC/ MB28-004895) (Nacala, Mozambique). Photo A and B, courtesy of B. Picton; photo C and K courtesy of Y.Tibiriça; photo D courtesy of V. Fraser; photo E courtesy of M. Caballer; photo F courtesy of G. Rouse; photo G and J, courtesy of N. Baưini; photo H courtesy of S. Thiebaud; photo I by F. Silva.