Marioniinae Silva et al., 2023

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 : 467-468

Subfamily Marioniinae Silva et al. , subfam. nov.

Zoobank registration: urn:lsid:zoobank.org:act:CAFEB7CF-064B-41A9-A25E-A3C2D9B1961B .

Diagnosis: True stomach plates present.

Morphology: Notum smooth or tuberculate. Rachidian tooth uni- or tricuspid, smooth or denticulate. Masticatory border of the jaws denticulate. First lateral tooth smooth, hooked and sharp. True stomach plates present. ODG complex cladohepatic or holohepatic. Ampulla and bursa copulatrix large. Gonopore at one-third of body length, furthest from rhinophores. Anus at middle of body length; nephroproct oħen above anus.

Genera included in this study: Marionia , Marioniopsis and Paratritonia .

Remarks: Based on our integrative approach, the plate-bearing tritoniids are a separate and morphologically distinct clade from the plateless species ( Fig. 2 ). This group is raised to the subfamily level as the monophyletic Marioniinae and characterized by the presence of true stomach plates. The true stomach plates of marioniids are thick, cuticular structures aưached to a belt or girdle and are oħen found near the openings between the digestive gland and the stomach. Gosliner (1994) suggested the presence of stomach plates in Cladobranchia as a plesiomorphic condition, as they are common in this group. Similar cuticular structures are also found, for example, in the family Tethydidae and in some genera of Cladobranchia , e.g. Melibe Rang 1829 (Rudman 1998, Gosliner and Pola 2012). However, we consider the presence of true stomach plates in the marioniids to be an apomorphic condition, consistent with the basal position of the Pleurobranchidae in our phylogenetic analyses ( Fig. 2 ).

Marioniidsaredividedintothreegenera: Marionia , Marioniopsis and Paratritonia . They may be distinguished from each other by the rachidian tooth morphology (tricuspid smooth in Marionia , tricuspid denticulate in Marioniopsis and unicuspid denticulate in Paratritonia ), masticatory borders of the jaw (denticles are sharp and triangular or rounded in Marionia , blunt and rounded or rod-shaped in Marioniopsis , and ‘faint scales’ in Paratritonia ) and digestive system arrangement (see remarks for Marionia ahead).

The taxonomic status of Indo-Pacific marioniids is in a remarkable state of taxonomic confusion resulting from (1) incomplete descriptions, (2) numerous sequenced unnamed species, (3) numerous specimens identified based on external morphology, (4) lack of morpho-anatomical studies that would help link names to living specimens and (5) pseudocryptic speciation that misleads taxonomy based on morphology. This has led to several controversies about the taxonomic validity of some species included in this study. For example, a literature search revealed that Marioniopsis arborescens has been used in the last two decades for some marioniids identified solely on the basis of external morphology ( Gosliner et al. 2008, 2015, Hullet et al. 2015, Tibiriçá et al. 2017). However, Marioniopsis arborescens was synonymized with Marioniopsis cyanobranchiata based on internal and external morphology long ago ( Odhner 1936), and since then no internal anatomical evidence has been presented to support the resurrection of the species. Similarly, the name Marionia distincta Bergh 1905 has been used to identify marioniids on the basis of external morphology ( Gosliner et al. 2008, 2015; Huleư et al. 2015, Tibiriçá et al. 2017), despite the established synonymy with Marioniopsis levis ( Odhner 1936) . These inconsistencies cause great confusion in the identification of these species. Because a broad taxonomic reassessment of the Indo-Pacific marioniids is beyond the scope of the present study, we have retained the original identification of the included marioniids from the Indo-Pacific region ( Table 1 ) and will address the taxonomy of our sequenced material in detail in future studies.

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.